Graph Data Structure And Algorithms

• A Graph is a non-linear data structure consisting of nodes and edges. The nodes are sometimes also referred to as vertices and the edges are lines or arcs that connect any two nodes in the graph. More formally a Graph can be defined as,A Graph consists of a finite set of vertices(or nodes) and set of Edges which connect a pair of nodes.
• In the above Graph, the set of vertices V = {0,1,2,3,4} and the set of edges E = {01, 12, 23, 34, 04, 14, 13}.
• Graphs are used to solve many real-life problems. Graphs are used to represent networks. The networks may include paths in a city or telephone network or circuit network. Graphs are also used in social networks like linkedIn, Facebook. For example, in Facebook, each person is represented with a vertex(or node). Each node is a structure and contains information like person id, name, gender, locale etc.

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Java Serialization and Customized Serialisation

• Serialization
• Serialization is a mechanism of converting the state of an object into a byte stream. Deserialization is the reverse process where the byte stream is used to recreate the actual Java object in memory. This mechanism is used to persist the object.
• The byte stream created is platform independent. So, the object serialized on one platform can be deserialized on a different platform.
• To make a Java object serializable we implement the java.io.Serializable interface.
• The ObjectOutputStream class contains writeObject() method for serializing an Object.
• The ObjectInputStream class contains readObject() method for deserializing an object.
• readResolve()
• This ensures that nobody can create another instance by serializing and deserializing the singleton.
• Advantages of Serialization
• To travel an object across a network.

• To save/persist state of an object.
• 
• 
  
• Only the objects of those classes can be serialized which are implementing java.io.Serializable interface. Serializable is a marker interface (has no data member and method). It is used to “mark” java classes so that objects of these classes may get certain capability.
• Other examples of marker interfaces are:- Cloneable and Remote.
• Points to remember
•  If a parent class has implemented Serializable interface then child class doesn’t need to implement it but vice-versa is not true.
• Only non-static data members are saved via Serialization process.
• Static data members and transient data members are not saved via Serialization process.So, if you don’t want to save value of a non-static data member then make it transient.
•  Constructor of object is never called when an object is deserialized.
• SerialVersionUID
• The Serialization runtime associates a version number with each Serializable class called a SerialVersionUID, which is used during Deserialization to verify that sender and reciever of a serialized object have loaded classes for that object which are compatible with respect to serialization. 
• If the reciever has loaded a class for the object that has different UID than that of corresponding sender’s class, the Deserialization will result in an InvalidClassException. A Serializable class can declare its own UID explicitly by declaring a field name.
• Example
• // Java program to illustrate loss of information // because of transient keyword. import java.io.*; class GfgAccount implements Serializable { String username = "gfg_admin"; transient String pwd = "geeks"; } class CustomizedSerializationDemo { public static void main(String[] args) throws Exception { GfgAccount gfg_g1 = new GfgAccount(); System.out.println("Username : " + gfg_g1.username + " Password : " + gfg_g1.pwd); FileOutputStream fos = new FileOutputStream("abc.ser"); ObjectOutputStream oos = new ObjectOutputStream(fos); // writeObject() method present in GfgAccount class // will be automatically called by jvm oos.writeObject(gfg_g1); FileInputStream fis = new FileInputStream("abc.ser"); ObjectInputStream ois = new ObjectInputStream(fis); // readObject() method present GfgAccount class // will be automatically called by jvm GfgAccount gfg_g2 = (GfgAccount)ois.readObject(); System.out.println("Username : " + gfg_g2.username + " Password : " + gfg_g2.pwd); } } ############### OUTPUT ############### Username : gfg_admin Password : geeks Username : gfg_admin Password : null
• Customized Serialisation
• During serialization, there may be data loss if we use the ‘transient’ keyword. ‘Transient’ keyword is used on the variables which we don’t want to serialize. But sometimes, it is needed to serialize them in a different manner than the default serialization (such as encrypting before serializing etc.), in that case, we have to use custom serialization and deserialization.
• Customized serialization can be implemented using the following two methods:
• private void writeObject(ObjectOutputStream oos) throws Exception: 
• This method will be executed automatically by the jvm(also known as Callback Methods) at the time of serialization. Hence to perform any activity during serialization, it must be defined only in this method.
• private void readObject(ObjectInputStream ois) throws Exception:
•  This method will be executed automatically by the jvm(also known as Callback Methods) at the time of deserialization. Hence to perform any activity during deserialization, it must be defined only in this method.
• Example
• import java.io.*; class GfgAccount implements Serializable { String username = "gfg_admin"; transient String pwd = "geeks"; // Performing customized serialization using the below two methods: // this method is executed by jvm when writeObject() on // Account object reference in main method is // executed by jvm. private void writeObject(ObjectOutputStream oos) throws Exception { // to perform default serialization of Account object. oos.defaultWriteObject(); // epwd (encrypted password) String epwd = "123" + pwd; // writing encrypted password to the file oos.writeObject(epwd); } // this method is executed by jvm when readObject() on // Account object reference in main method is executed by jvm. private void readObject(ObjectInputStream ois) throws Exception { // performing default deserialization of Account object ois.defaultReadObject(); // deserializing the encrypted password from the file String epwd = (String)ois.readObject(); // decrypting it and saving it to the original password // string starting from 3rd index till the last index pwd = epwd.substring(3); } } class CustomizedSerializationDemo { public static void main(String[] args) throws Exception { GfgAccount gfg_g1 = new GfgAccount(); System.out.println("Username :" + gfg_g1.username + " Password :" + gfg_g1.pwd); FileOutputStream fos = new FileOutputStream("abc.ser"); ObjectOutputStream oos = new ObjectOutputStream(fos); // writeObject() method on Account class will // be automatically called by jvm oos.writeObject(gfg_g1); FileInputStream fis = new FileInputStream("abc.ser"); ObjectInputStream ois = new ObjectInputStream(fis); GfgAccount gfg_g2 = (GfgAccount)ois.readObject(); System.out.println("Username :" + gfg_g2.username + " Password :" + gfg_g2.pwd); } } ############### OUTPUT ############### Username :gfg_admin Password :geeks Username :gfg_admin Password :geeks

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Java Innerclass

• Inner class is a class defined inside other class and act like a member of the enclosing class.
• There are two main types of inner classes
• Static member class
• Inner class
• Member class
• Anonymous class
• Local class
• Static member class
• A static member class behaves much like an ordinary top-level class, except that it can access the static members of the outer. 
• Outer class can access all inner class fields by referring Inner Class.(InnerA.printAnimal()). But inner class can access all static outer class properties and methods directly.
• Both inner and outer classes can access others private properties and methods.
• The static nested class can be accessed as the other static members of the enclosing class without having an instance of the outer class.
•  The static class can contain non-static and static members and methods.
• InnerClassTest1.java
• public class InnerClassTest1 { private static int out = 1; public static class innerA { private static int number = 10; static void printAnimal(String animal) { System.out.println(out); System.out.println(animal); test(); } } private static void test() { System.out.println(innerA.number); } }
• App.java
• public class App { public static void main(String[] args) { InnerClassTest1.innerA.printAnimal("Tiger"); } }
• Member class
• Need to create Instance access properties and class out side the method.
• Need Outer class object to create inner class object.
• The member class can be declared as public, private, protected, final and abstract. E.g.
• InnerClassTest2.java
• public class InnerClassTest2 { private int out = 1; public class MemberClass { private void showName() { System.out.println("Sonu"); System.out.println(out); } } public void test() { MemberClass m = new MemberClass(); m.showName(); } }
• App.java
• public class App { public static void main(String[] args) { InnerClassTest2 o = new InnerClassTest2(); InnerClassTest2.MemberClass m = o.new MemberClass(); } }
• Local class
• It can be accessed only from same method.
• Local classes cannot be public, private, protected, or static. (No access modifiers)
• Local class can access all outer class properties and methods.
• local class can access local variables and parameters of the enclosing method that are effectively final.
• InnerClassTest3.java
• public class InnerClassTest3 { int outerNumber = 1; public void methodTest() { int methodNumber = 2; class MethodLocalClass { private void showName() { System.out.println("SONU"); System.out.println(outerNumber); System.out.println(methodNumber); test(); } } methodNumber = 2; //error outerNumber =3; //will work MethodLocalClass m = new MethodLocalClass(); m.showName(); } public void test() { System.out.println("TEST"); } }
• Anonymous class
• These are local classes which are automatically declared and instantiated in the middle of an expression. 
• Also, like local classes, anonymous classes cannot be public, private, protected, or static. 
• They can define in the  arguments to the constructor of the outerclass, but cannot otherwise have a constructor.
• They can implement only one interface or extend a class.
• Anonymous class cannot define any static fields, methods, or classes, except for static final constants.
• xxxx

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JDBC Interview Questions

1. ACID Properties in DBMS?
1. A transaction is a single logical unit of work which accesses and possibly modifies the contents of a database. Transactions access data using read and write operations.In order to maintain consistency in a database, before and after transaction, certain properties are followed. These are called ACID properties.
2. Atomicity
1. By this, we mean that either the entire transaction takes place at once or doesn’t happen at all. There is no midway i.e. transactions do not occur partially. Each transaction is considered as one unit and either runs to completion or is not executed at all. 
3. Consistency
1. This means that integrity constraints must be maintained so that the database is consistent before and after the transaction. It refers to correctness of a database. 
4. Isolation
1. This property ensures that multiple transactions can occur concurrently without leading to inconsistency of database state. Transactions occur independently without interference. Changes occurring in a particular transaction will not be visible to any other transaction until that particular change in that transaction is written to memory or has been committed. This property ensures that the execution of transactions concurrently will result in a state that is equivalent to a state achieved these were executed serially in some order.
5. Durability
1. This property ensures that once the transaction has completed execution, the updates and modifications to the database are stored in and written to disk and they persist even is system failure occurs. These updates now become permanent and are stored in a non-volatile memory.
6. The effects of the transaction, thus, are never lost.

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Hibernate Interview Questions

1. filter employees with same salary count greater than five (group by salary) using hibernate criteria?
1. Session session = getCurrentSession(); ProjectionList projectionList = Projections.projectionList(); projectionList.add(Projections.groupProperty("totalCode")) .add(Projections.groupProperty("activityCode")) .add(Projections.sum("amount")) .add(Projections.rowCount()); Criteria criteria = session.createCriteria(Payment.class); criteria.setProjection(projectionList); List payments = criteria.list(); for (Object[] payment : payments) { System.out.println("totalCode: " + payment[0]); System.out.println("activityCode: " + payment[1]); System.out.println("amountSum: " + payment[2]); System.out.println("rowCount: " + payment[3]); }
2. What is Hibernate N+1 Problems and its Solution?
1. Hibernate n+1 problems only comes for one to many relationship.
2. Let us see this problem by example – We have Department table with a one-to-many relationship with Employee. One Department may have many Employees.
3. We have written the Hibernate Department Entity as below.
4. @Entity public class Department { private Long id; @OneToMany private Employee[] Employees; }
5. So now you want to print out all the details of Employee models. A native O/R implementation would SELECT all Department and then do N additional SELECTs for getting the information of Employee for each department.
6. -- To Get all Departments SELECT * FROM Department; -- To get each Employee, get Employee details SELECT * FROM Employee WHERE Employee.departmentId = ?
7. As you see, the N+1 problem can happen if the first query populates the primary object and the second query populates all the child objects for each of the unique primary objects returned.
8. Solution for Hibernate N+1 Problem
1. Using HQL fetch join
1. You can use the fetch while using the HQL as below example.
1. from Department d join fetch d.employees Employee
2. Hibernate Generated SQL would be similer as –
3. SELECT * FROM Department d LEFT OUTER JOIN Employee e ON d.id = d.department_id
1. Using Criteria query
1. Criteria criteria = session.createCriteria(Department.class); criteria.setFetchMode("employees", FetchMode.EAGER);
2. In both above cases, the query returns a list of Department objects with the Employee initialized, and only one query needs to be run to return all the Department and Employee information required.

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Java program to capitalize first letter of each word in string

public class FirstWordUpperCase { public static void main(String[] args) { System.out.println(changeString("how are you man")); } private static String changeString(String str) { StringBuffer sb = new StringBuffer(); String[] arr = str.split("\\s"); for (int i = 0; i < arr.length; i++) { sb.append(Character.toUpperCase(arr[i].charAt(0))). append(arr[i].substring(1)).append(" "); } return sb.toString(); } }

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JSP Interview Questions

1. How to disable caching on back button of the browser?
1. <% response.setHeader(“Cache-Control”,”no-store”); response.setHeader(“Pragma”,”no-cache”); response.setHeader (“Expires”, “0”); //prevents caching at the proxy server %>
2. 
   

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Hibernate one to one mapping

1. In this kind of association, a foreign key column is created in owner entity. For example, if we make EmployeeEntity owner, then a extra column "ACCOUNT_ID" will be created in Employee table. This column will store the foreign key for Account table.
2. To make such association, refer the Account entity in EmployeeEntity class as follow:
3. @OneToOne @JoinColumn(name="ACCOUNT_ID") private AccountEntity account;
4. @JoinColumn
2. The join column is declared with the @JoinColumn annotation which looks like the @Column annotation, It is used in column owner column and mapped by used in other table. It has one more parameters named referencedColumnName. This parameter declares the column in the targeted entity that will be used to the join.
5. mappedBy
1.  mappedBy is used. ‘mappedBy’ refers to the property name of the association on the owner side.AccountEntity.java
2. @OneToOne(mappedBy="account") private EmployeeEntity employee;
3. 
   

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Hibernate Many-To-One Bidirectional

1. One table has a foreign key column that references the primary key of associated table.In Bidirectional relationship, both side navigation is possible.
2. We are discussing an example of Student and University relationship. Many student can enroll at one University. And one University can have many students. 
3. @Entity @Table(name = "STUDENT") public class Student { @Id @GeneratedValue @Column(name = "STUDENT_ID") private long id; @Column(name = "FIRST_NAME") private String firstName; @ManyToOne(optional = false) @JoinColumn(name = "UNIVERSITY_ID") private University university; ------------------------ ------------------------ } @Entity @Table(name = "UNIVERSITY") public class University { @Id @GeneratedValue @Column(name = "UNIVERSITY_ID") private long id; @Column(name = "NAME") private String name; @Column(name = "COUNTRY") private String country; @OneToMany(mappedBy = "university", cascade = CascadeType.ALL) private List students; }
4. @JoinColumn says that Student table will contain a separate column UNIVERSITY_ID which will eventually act as a foreign key reference to primary key of University table

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Many to Many Annotation

1. In this scenario, any given employee can be assigned to multiple projects and a project may have multiple employees working for it, leading to a many-to-many association between the two.
2. We have an employee table with employee_id as its primary key and a project table with project_id as its primary key. A join table employee_project is required here to connect both sides.
3. The model classes Employee and Project need to be created with JPA annotations:
1. @Entity @Table(name = "Employee") public class Employee { // ... @ManyToMany(cascade = { CascadeType.ALL }) @JoinTable( name = "Employee_Project", joinColumns = { @JoinColumn(name = "employee_id") }, inverseJoinColumns = { @JoinColumn(name = "project_id") } ) Set projects = new HashSet<>(); // standard constructor/getters/setters } @Entity @Table(name = "Project") public class Project { // ... @ManyToMany(mappedBy = "projects") private Set employees = new HashSet<>(); // standard constructors/getters/setters }
4. Both the Employee class and Project classes refer to one another, which means that the association between them is bidirectional.
5. In order to map a many-to-many association, we use the @ManyToMany, @JoinTable and @JoinColumn annotations. 
6. @ManyToMany
1. The @ManyToMany annotation is used in both classes to create the many-to-many relationship between the entities.
7. @JoinTable
1.  In our example, the owning side is Employee so the join table is specified on the owning side by using the @JoinTable annotation in Employee class
8. @JoinColumn
1. The @JoinColumn annotation is used to specify the join/linking column with the main table. Here, the join column is employee_id and project_id is the inverse join column since Project is on the inverse side of the relationship
9. mappedBy
1. In the Project class, the mappedBy attribute is used in the @ManyToMany annotation to indicate that the employees collection is mapped by the projects collection of the owner side

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LinkedList and Index

1. They have a logical index, yes - effectively the number of times you need to iterate, starting from the head, before getting to that node.
2. it can't directly search using index of the object
3. Typically O(1) access by index is performed by using an array lookup, and in the case of a linked list there isn't an array - there's just a chain of nodes. To access a node with index N, you need to start at the head and walk along the chain N times... which is an O(N) operation.
4. import java.util.LinkedList; import java.util.List; import java.util.function.Supplier; import java.util.stream.Collectors; import java.util.stream.IntStream; public class LnkedListNthh { public static void main(String[] args) { LnkedListNthh app = new LnkedListNthh(); LinkedList list = app.createList(); app.nthElement(list, 2); app.SecondLastElement(list); } private void nthElement(LinkedList list, Integer n) { list.get(n); System.out.println(n + "th Element is " + list.get(n)); } private void SecondLastElement(LinkedList list) { System.out.println("SecondLastElement = " + list.get(list.size() - 1)); } private LinkedList createList() { LinkedList list = new LinkedList(); Supplier> supplier = () -> new LinkedList(); return (LinkedList) IntStream.range(2, 102).boxed().collect(Collectors.toCollection(supplier)); } }

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Java 8 New

1. Function Interface
1.  Java.util.function has special interface like bleow, it contains generic methods used as type for lambda expression with same type and signature.
2. An interface with exactly one abstract method is called Functional Interface.
3. @FunctionalInterface annotation is added so that we can mark an interface as functional interface.
4.  If  we try to have more than one abstract method, it throws compiler error.
5. The major benefit of java 8 functional interfaces is that we can use lambda expressions to instantiate them and avoid using bulky anonymous class implementation.
6. Java 8 has defined a lot of functional interfaces in java.util.function package. Some of the useful java 8 functional interfaces are Runnable, Consumer, Supplier, Function and Predicate
1. Custom
1. @FunctionalInterface public interface Square { public int calculate(int number); } // Custom Square sq = (i) -> (i * i); int result = sq.calculate(2); System.out.println(result);
2. Runnable
1. Thread t = new Thread(() -> { System.out.println("Thread Running"); }); t.start();
3. Predecate Interface
1. The Functional Interface PREDICATE is defined in the java.util.Function package.It improves manageability of code, helps in unit-testing them separately, and contain some methods like:
1. isEqual(Object targetRef) : Returns a predicate that tests if two arguments are equal according to Objects.equals(Object, Object).
2. and(Predicate other) : Returns a composed predicate that represents a short-circuiting logical AND of this predicate and another.
3. negate() : Returns a predicate that represents the logical negation of this predicate.
4. or(Predicate other) : Returns a composed predicate that represents a short-circuiting logical OR of this predicate and another.
5. test(T t) : Evaluates this predicate on the given argument.boolean test(T t)
2. // Simple Predicate Predicate lesserThan = (i) -> (i > 10); System.out.println(lesserThan.test(11)); // Predicate Chaining Predicate lessThan = (i) -> (i < 10); Predicate greaterThan = (i) -> (i > 5); boolean result = lesserThan.and(greaterThan).test(6); System.out.println(result); // negation boolean result2 = lesserThan.and(greaterThan).negate().test(6); System.out.println(result2); Predicate equals = (i) -> (i == 2); boolean result3 = equals.test(2); System.out.println(result3);
2. Static methods and Default methods
1. Default methods
1. Java 8 interface changes include static methods and default methods in interfaces. Prior to Java 8, we could have only method declarations in the interfaces. But from Java 8, we can have default methods and static methods in the interfaces.
2. For creating a default method in java interface, we need to use “default” keyword with the method signature. For example,
3. public interface Interface2 { void method2(); default void log(String str){ System.out.println("I2 logging::"+str); } }
2. Static methods 
1. Java interface static method is similar to default method except that we can’t override them in the implementation classes.
2. public interface MyData { default void print(String str) { if (!isNull(str)) System.out.println("MyData Print::" + str); } static boolean isNull(String str) { System.out.println("Interface Null Check"); return str == null ? true : "".equals(str) ? true : false; } }
3. Java interface static methods are good for providing utility methods, for example null check, collection sorting etc.
3. Abstract Class Needs
1. Abstract class can define constructor. They are more structured and can have a state associated with them. 
2. The constraint on the default method is that it can be implemented only in the terms of calls to other interface methods, with no reference to a particular implementation's state. So the main use case is higher-level and convenience methods.

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Angular 6 CRUD Application

1. Angular CLI Useful Commands
1. ng g component my-new-component
2. ng g directive my-new-directive
3. ng g pipe my-new-pipe
4. ng g service my-new-service
5. ng g class my-new-class
6. ng g guard my-new-guard
7. ng g interface my-new-interface
8. ng g enum my-new-enum
9. ng g module my-module
2. Create components. Template, component and js file will be generated with this and Module will be added to @ngModule decorations decalarion part of app.module.ts.
1. ng g component login ng g component add-user ng g component edit-user ng g component list-user
2. app.module.ts
3. import { NgModule } from '@angular/core'; import { Routes, RouterModule } from '@angular/router'; import { LoginComponent } from "./login/login.component"; import { AddUserComponent } from "./add-user/add-user.component"; import { EditUserComponent } from "./edit-user/edit-user.component"; import { ListUserComponent } from "./list-user/list-user.component"; const routes: Routes = [ { path: 'login', component: LoginComponent }, { path: 'add-user', component: AddUserComponent }, { path: 'edit-user', component: EditUserComponent }, { path: 'list-user', component: ListUserComponent }, { path: '', component: LoginComponent } ]; @NgModule({ imports: [RouterModule.forRoot(routes)], exports: [RouterModule] }) export class AppRoutingModule { }
4. Following is our routing configurtion.We have configured to use LoginComponent as a default component.Also, do not forget to include it in the main module - app.module.ts
5. app.routing.ts
6. import { NgModule } from '@angular/core'; import { Routes, RouterModule } from '@angular/router'; import { LoginComponent } from "./login/login.component"; import { AddUserComponent } from "./add-user/add-user.component"; import { EditUserComponent } from "./edit-user/edit-user.component"; import { ListUserComponent } from "./list-user/list-user.component"; const routes: Routes = [ { path: 'login', component: LoginComponent }, { path: 'add-user', component: AddUserComponent }, { path: 'edit-user', component: EditUserComponent }, { path: 'list-user', component: ListUserComponent }, { path: '', component: LoginComponent } ]; @NgModule({ imports: [RouterModule.forRoot(routes)], exports: [RouterModule] }) export class AppRoutingModule { }
3. Create model user.model.ts
1. ng g class model/User
2.  user.model.ts
3. export class User { id: number; firstName: string; lastName: string; email: string; }
4. Create Service service/user.service.ts
1. ng g service service/UserService
2. We can make web api call using HttpClent package in service class by the use of model User
3. user.service.ts 
4. import { Injectable } from '@angular/core'; import { HttpClient } from '@angular/common/http'; import { User } from '../model/user'; @Injectable({ providedIn: 'root' }) export class UserServiceService { constructor(private http: HttpClient) { } baseUrl: string = 'http://localhost:8080/user-portal/users'; getUsers() { return this.http.get(this.baseUrl); } getUserById(id: number) { return this.http.get(this.baseUrl + '/' + id); } createUser(user: User) { return this.http.post(this.baseUrl, user); } updateUser(user: User) { return this.http.put(this.baseUrl + '/' + user.id, user); } deleteUser(id: number) { return this.http.delete(this.baseUrl + '/' + id); } }
5. Edit Html and component class to make the application
1. add-user.component.html
6. 2.    add-user.component.ts
1. import { Component, OnInit } from '@angular/core'; import {FormBuilder, FormGroup, Validators} from "@angular/forms"; import {UserService} from "../service/user.service"; import {first} from "rxjs/operators"; import {Router} from "@angular/router"; @Component({ selector: 'app-add-user', templateUrl: './add-user.component.html', styleUrls: ['./add-user.component.css'] }) export class AddUserComponent implements OnInit { constructor(private formBuilder: FormBuilder,private router: Router, private userService: UserService) { } addForm: FormGroup; ngOnInit() { this.addForm = this.formBuilder.group({ id: [], email: ['', Validators.required], firstName: ['', Validators.required], lastName: ['', Validators.required] }); } onSubmit() { this.userService.createUser(this.addForm.value) .subscribe( data => { this.router.navigate(['list-user']); }); } }
7. Adding Materials
1. With the release of Angular 6, we can directly run ng add @angular/material command to add material design capabilities to an existing Angular application. By executing below command we will be installing Angular Material and the corresponding theming into the project.

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Angular6 Routing

• To generate new component employee. Go to app root in CLI and run below command
• ng g c employee/create-employee --spec=false --flat=true ng g c employee/list-employees --spec=false --flat=true
• component.ts, html and css files will be genarated in employee folder in app and it will add List Employee and Create Employee components in app.module.ts as below
• app.module.ts
• import { BrowserModule } from '@angular/platform-browser'; import { NgModule } from '@angular/core'; import { AppRoutingModule } from './app-routing.module'; import { AppComponent } from './app.component'; import { CreateEmployeeComponent } from './employee/create-employee.component'; import { ListEmployeesComponent } from './employee/list-employees.component'; @NgModule({ declarations: [ AppComponent, CreateEmployeeComponent, ListEmployeesComponent ], imports: [ BrowserModule, AppRoutingModule ], providers: [], bootstrap: [AppComponent] }) export class AppModule { }
• Generate routing module to app. It will create app-routing.module.ts file and add Routing  to app.module.ts
• ng g m app-routing --flat=true --module=app
• Inside app-routing.module.ts, add  RouterModule object and call forRoot Method as below.
• import { NgModule } from '@angular/core'; import { Routes, RouterModule } from '@angular/router'; import { ListEmployeesComponent } from './employee/list-employees.component'; import { CreateEmployeeComponent } from './employee/create-employee.component'; const routes: Routes = [ {path: 'list', component: ListEmployeesComponent}, {path: 'create', component: CreateEmployeeComponent} ]; @NgModule({ imports: [RouterModule.forRoot(routes)], exports: [RouterModule] }) export class AppRoutingModule { }
• Go to app.component.html and add new routes using routerLink tag

• 
  

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Angular Interview Questions

1. define AngularJS?
1. AngularJS is an open-source JavaScript framework designed for creating dynamic single web page applications with fewer lines of code. 
2. What is Angular 2?
1. Angular is a framework to build large scale and high performance web application while keeping them as easy-to-maintain.
2. Components − The earlier version of Angular had a focus of Controllers but now has changed the focus to having components over controllers. Components help to build the applications into many modules. This helps in better maintaining the application over a period of time.
3. TypeScript − The newer version of Angular is based on TypeScript. This is a superset of JavaScript and is maintained by Microsoft.
4. Services − Services are a set of code that can be shared by different components of an application. So for example if you had a data component that picked data from a database, you could have it as a shared service that could be used across multiple applications.
3. What are the key components of Angular 2?
1. Modules − This is used to break up the application into logical pieces of code. Each piece of code or module is designed to perform a single task.
2. Component − This can be used to bring the modules together.
3. Templates − This is used to define the views of an Angular JS application.
4. Metadata − This can be used to add more data to an Angular JS class.
5. Service − This is used to create components which can be shared across the entire application.
4. Explain Modules in Angular 2.
1. Modules are used in Angular JS to put logical boundaries in your application. Hence, instead of coding everything into one application, you can instead build everything into separate modules to separate the functionality of your application. A module is made up of the following parts −
1. Bootstrap array − This is used to tell Angular JS which components need to be loaded so that its functionality can be accessed in the application. Once you include the component in the bootstrap array, you need to declare them so that they can be used across other components in the Angular JS application.
2. Export array − This is used to export components, directives, and pipes which can then be used in other modules.
3. Import array − Just like the export array, the import array can be used to import the functionality from other Angular JS modules.
5. Explain Components in Angular 2.
1. Each application consists of Components. Each component is a logical boundary of functionality for the application. You need to have layered services, which are used to share the functionality across components.Following is the anatomy of a Component. A component consists of −
1. Class − This is like a C or Java class which consists of properties and methods.
2. Metadata − This is used to decorate the class and extend the functionality of the class.
3. Template − This is used to define the HTML view which is displayed in the application.
6. What are Angular 2 directives? Explain with examples?
1. A directive is a custom HTML element that is used to extend the power of HTML. Angular 2 has the following directives that get called as part of the BrowserModule module.
1. ngIf
1. The ngif element is used to add elements to the HTML code if it evaluates to true, else it will not add the elements to the HTML code.
2. *ngIf = 'expression'
2. ngFor
1. The ngFor element is used to elements based on the condition of the For loop.
2. *ngFor = 'let variable of variablelist'
7. How will you handle errors in Angular 2 applications?
1. Angular 2 applications have the option of error handling. This is done by including the ReactJS catch library and then using the catch function.
2. The catch function contains a link to the Error Handler function.
3. In the error handler function, we send the error to the console. We also throw the error back to the main program so that the execution can continue.
4. Now, whenever you get an error it will be redirected to the error console of the browser.
8. What is routing?
1. Routing helps in directing users to different pages based on the option they choose on the main page. Hence, based on the option they choose, the required Angular Component will be rendered to the user.
2. product.component.ts
3. import { Component } from '@angular/core'; @Component ({ selector: 'my-app', template: 'Products', }) export class Appproduct { }
4. app.module.ts
5. import { NgModule } from '@angular/core'; import { BrowserModule } from '@angular/platform-browser'; import { AppComponent } from './app.component'; import { Appproduct } from './product.component'; import { AppInventory } from './Inventory.component'; import { RouterModule, Routes } from '@angular/router'; const appRoutes: Routes = [ { path: 'Product', component: Appproduct }, { path: 'Inventory', component: AppInventory }, ]; @NgModule ({ imports: [ BrowserModule, RouterModule.forRoot(appRoutes)], declarations: [ AppComponent,Appproduct,AppInventory], bootstrap: [ AppComponent ] }) export class AppModule { }
6. app.component.ts
7. [routerLink] = "['/Product']
9. What is Dependency Injection? Explain with example?
1. Dependency injection is the ability to add the functionality of components at runtime. Lets take a look at an example and the steps used to implement dependency injection.
2. Create a separate class which has the injectable decorator. The injectable decorator allows the functionality of this class to be injected and used in any Angular JS module.
1. @Injectable() export class classname { }
3.  Next in your appComponent module or the module in which you want to use the service, you need to define it as a provider in the @Component decorator.
1. @Component ({ providers : [classname] })
10. Explain tsconfig.json file?
1. This file is used to give the options about TypeScript used for the Angular JS project.
2. { 'compilerOptions': { 'target': 'es5', 'module': 'commonjs', 'moduleResolution': 'node', 'sourceMap': true, 'emitDecoratorMetadata': true, 'experimentalDecorators': true, 'lib': [ 'es2015', 'dom' ], 'noImplicitAny': true, 'suppressImplicitAnyIndexErrors': true } }
2. The target for the compilation is es5 and that is because most browsers can only understand ES5 typescript.
3. The sourceMap option is used to generate Map files, which are useful when debugging. Hence, during development it is good to keep this option as true.
4. The "emitDecoratorMetadata": true and "experimentalDecorators": true is required for Angular JS decorators. If not in place, Angular JS application will not compile.
11.  package.json file?
1. This file contains information about Angular 2 project. Following are the typical settings in the file..
2. { "name": "angular-quickstart", "version": "1.0.0", "description": "QuickStart package.json from the documentation, supplemented with testing support", "scripts": { "build": "tsc -p src/", "build:watch": "tsc -p src/ -w", "build:e2e": "tsc -p e2e/", "serve": "lite-server -c=bs-config.json", "serve:e2e": "lite-server -c=bs-config.e2e.json", "prestart": "npm run build", "start": "concurrently \"npm run build:watch\" \"npm run serve\"", "pree2e": "npm run build:e2e", "e2e": "concurrently \"npm run serve:e2e\" \"npm run protractor\" --killothers --success first", "preprotractor": "webdriver-manager update", "protractor": "protractor protractor.config.js", "pretest": "npm run build", "test": "concurrently \"npm run build:watch\" \"karma start karma.conf.js\"", "pretest:once": "npm run build", "test:once": "karma start karma.conf.js --single-run", "lint": "tslint ./src/**/*.ts -t verbose" }, "keywords": [], "author": "", "license": "MIT", "dependencies": { "@angular/common": "<2 .4.0="" angular-in-memory-web-api="" angular="" canonical-path="" code="" compiler="" concurrently="" core-js="" core="" devdependencies="" forms="" http="" jasmine-core="" jasmine="" karma-chrome-launcher="" karma-cli="" karma-jasmine-html-reporter="" karma-jasmine="" karma="" lite-server="" lodash="" node="" platform-browser-dynamic="" platform-browser="" protractor="" repository="" rimraf="" router="" rxjs="" systemjs="" tslint="" types="" typescript="" zone.js="">
4. There are two types of dependencies, first is the dependencies and then there are dev dependencies. The dev ones are required during the development process and the others are needed to run the application.
5. The "build:watch": "tsc -p src/ -w" command is used to compile the typescript in the background by looking for changes in the typescript files.
12. Explain systemjs.config.json file.
1. This file contains the system files required for Angular JS application. This loads all the necessary script files without the need to add a script tag to the html pages. The typical files will have the following code.
1. ** * System configuration for Angular samples * Adjust as necessary for your application needs. */ (function (global) { System.config({ paths: { // paths serve as alias 'npm:': 'node_modules/' }, // map tells the System loader where to look for things map: { // our app is within the app folder app: 'app', // angular bundles '@angular/core': 'npm:@angular/core/bundles/core.umd.js', '@angular/common': 'npm:@angular/common/bundles/common.umd.js', '@angular/compiler': 'npm:@angular/compiler/bundles/compiler.umd.js', '@angular/platform-browser': 'npm:@angular/platformbrowser/bundles/platform-browser.umd.js', '@angular/platform-browser-dynamic': 'npm:@angular/platform-browserdynamic/bundles/platform-browser-dynamic.umd.js', '@angular/http': 'npm:@angular/http/bundles/http.umd.js', '@angular/router': 'npm:@angular/router/bundles/router.umd.js', '@angular/forms': 'npm:@angular/forms/bundles/forms.umd.js', // other libraries 'rxjs': 'npm:rxjs', 'angular-in-memory-web-api': 'npm:angular-in-memory-web-api/bundles/inmemory-web-api.umd.js' }, // packages tells the System loader how to load when no filename and/or no extension packages: { app: { defaultExtension: 'js' }, rxjs: { defaultExtension: 'js' } } }); })(this);
2. 'npm:': 'node_modules/' tells the location in our project where all the npm modules are located.
3. The mapping of app: 'app' tells the folder where all our applications files are loaded.
13. app.module.ts file.
1. mport { NgModule } from '@angular/core'; import { BrowserModule } from '@angular/platform-browser'; import { AppComponent } from './app.component'; @NgModule({ imports: [ BrowserModule ], declarations: [ AppComponent ], bootstrap: [ AppComponent ] }) export class AppModule { }
3. The import statement is used to import functionality from the existing modules. Thus, the first 3 statements are used to import the NgModule, BrowserModule and AppComponent modules into this module.
4. The NgModule decorator is used to later on define the imports, declarations, and bootstrapping options.
5. The BrowserModule is required by default for any web based angular application.
6. The bootstrap option tells Angular which Component to bootstrap in the application.
14. Angular Life Cycle
2. ngOnChanges − When the value of a data bound property changes, then this method is called.
3. ngOnInit − This is called whenever the initialization of the directive/component after Angular first displays the data-bound properties happens.
4. ngDoCheck − This is for the detection and to act on changes that Angular can't or won't detect on its own.
5. ngAfterContentInit − This is called in response after Angular projects external content into the component's view.
6. ngAfterContentChecked − This is called in response after Angular checks the content projected into the component.
7. ngAfterViewInit − This is called in response after Angular initializes the component's views and child views.
8. ngAfterViewChecked − This is called in response after Angular checks the component's views and child views.
9. ngOnDestroy − This is the cleanup phase just before Angular destroys the directive/component.

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Remove common number from two arrays

• Need to remove common number 4 from both arrays
• Input
• int[] arr1 = { 1, 4, 6, 7, 8 };
• int[] arr2 = { 2, 4, 5, 9, 0 };
• Output
• int[] arr1 = { 1, 6, 7, 8 };
• int[] arr2 = { 2, 5, 9, 0 };

• RemoveCommonElements.java
• public class RemoveCommonElements { public static void main(String[] args) { RemoveCommonElements app = new RemoveCommonElements(); app.commonRemove(); } private void commonRemove() { int[] arr1 = { 1, 4, 6, 7, 8 }; int[] arr2 = { 2, 4, 5, 9, 0 }; for (int e : arr1) { if (contains(arr2, e)) { remove(arr1, e); remove(arr2, e); } } System.out.print(arr1); System.out.print(arr2); } private boolean contains(int[] arr, int e) { for (int i : arr) { if (i == e) { return true; } } return false; } private int[] remove(int[] arr, int e) { for (int i = 0; i < arr.length; i++) { if (arr[i] == e) { for (int j = i; j < arr.length-1; j++) { arr[j] = arr[j + 1]; } } } return arr; } } ######### RESULT ########## 1, 6, 7, 8, 8 2, 5, 9, 0 ,0
• In below example CopyOnWriteArrayList will be concurrent in type and ConcurrentModificationException can be prevent
• /** * Get UNION list * Get INTERSECTION LIST by retainAll //common elements * Remove intersection from union */ private static void removeCommonElements() { List list1 = Arrays.asList(1, 2, 3, 4, 5, 6); List list2 = Arrays.asList(10, 2, 3, 40, 50, 60); List union = new ArrayList(list1); union.addAll(list2); List intersection = new ArrayList<>(list1); // only common elements intersection.retainAll(list2); union.removeAll(intersection); System.out.println(union); }

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Inheritance and Conditions

1. When Parent throws Generic Exception and Child throws specific exception
1. Compiles and run successfully
2. public class Animal { public void eat() throws Exception { System.out.println("Animal Eating..."); } } public class Cat extends Animal { @Override public void eat() throws FileNotFoundException { System.out.println("Cat Eating ....."); } } public class App { public static void main(String[] args) throws Exception { Animal cat = new Cat(); cat.eat(); } } ######### RESULT ########## Cat Eating .....
2. When Parent throws specific exception and child throws generic exception
1. Compile time error
3. When Parent modifier is protected and child modifier is public
1. Compiles and run successfully
4. When Parent modifier is private and child modifier is public
1. Compile time error
5. When Parent modifier is public and child modifier is private
1. Compile time error

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Java clone object – cloning in java

• Java Object class comes with native clone() method that returns the copy of the existing instance.
• To use java object clone method, we have to implement the marker interface java.lang.Cloneable so that it won’t throw CloneNotSupportedException at runtime.
• Also Object clone is a protected method, so we will have to override it to use with other classes
• Student.java
• public class Student implements Cloneable { private int id; private String name; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } @Override protected Object clone() throws CloneNotSupportedException { return super.clone(); } }
• App.java
• public class App { public static void main(String[] args) throws CloneNotSupportedException { Student student1 = new Student(); student1.setId(1); student1.setName("Sonu"); Student student2 = (Student) student1.clone(); System.out.println(student2.getName()); if (student1.equals(student2)) { System.out.println("EQUAL"); } } }
• s1 == s2: false
• So s1 and s2 are two different object, not referring to same object. This is in agreement of the java clone object requirement.
• s1.name == s2.name: true
• So both s1 and s2 object variables refer to same object.
• Shallow copy
• Shallow copy is a bit-wise copy of an object. A new object is created that has an exact copy of the values in the original object. If any of the fields of the object are references to other objects, just the reference addresses are copied i.e., only the memory address is copied.
• Deep copy
• A deep copy copies all fields, and makes copies of dynamically allocated memory pointed to by the fields. A deep copy occurs when an object is copied along with the objects to which it refers.

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Structural design patterns

Structural design patterns are concerned with how classes and objects can be composed, to form larger structures.The structural design patterns simplifies the structure by identifying the relationships.These patterns focus on, how the classes inherit from each other and how they are composed from other classes.

• Adapter Pattern 
• An Adapter Pattern says that just "converts the interface of a class into another interface that a client wants".
• In other words, to provide the interface according to client requirement while using the services of a class with a different interface.
• The Adapter Pattern is also known as Wrapper.

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Spring Transaction Management

• Declarative Transaction Management

• Declarative transaction management is the most common Spring implementation as it has the least impact on application code.
• The XML declarative approach configures the transaction attributes in a Spring bean configuration file. Declarative transaction management in Spring has the advantage of being less invasive. 
•  There is no need for changing application code when using declarative transactions.       All you have to do is to modify the application context.
• Methods
•  XML based
• Annotations based
• Steps
• Step 1: Define a transaction manager in spring.xml
• <bean class="org.springframework.jdbc.datasource.DataSourceTransactionManager" id="txManager"/>
• Step 2: Turn on support for transaction annotations in spring.xml
• <tx:annotation-driven transaction-manager="txManager"/>
•  Step 3: Add the @Transactional annotation to the createEmployee Method      @Transactional
• public int createEmployee(Employee employee) {

..

• Annotation attributes
• Transaction readOnly
• If you don’t explicitly set readOnly attribute to true, you will have read/write transactions.Its always better to explicitly specify the readOnly attribute, as we have noticed some massive performance improvements with Hibernate because of this.
• Transaction propagation
• Transaction propagation is REQUIRED by default, which means that the same transaction will propagate from a transactional caller to transactional callee. It will create a new transaction or reuse the one if available. For example, if a read-only transaction calls a read-write transaction method, the whole transaction will be read-only.
• Depending on the transaction propagation attribute (like for REQUIRES_NEW), sometimes the existing transaction is suspended/paused at some point, a new one is always started and eventually committed, and after that the first transaction is resumed.
• Isolation Level
• Isolation level defines a contract between transactions.
• Read Uncommitted – Allows dirty reads, when a transaction is not yet committed by a thread and another thread is reading the dirty data.
• Read Committed – Does not allow dirty reads. Only lets a thread to read values which have already been committed by other running transactions in another threads.
• Repeatable Read – If the same data is read twice in the same transaction, it will always be the same. This level guarantees that any data once read cannot change.
• Serializable – Transactions occur with locking at all levels (read, range and write locking), because of which they are executed in a fixed sequence. It doesn’t allow concurrent transactions and leads to a performance hit.

•  Programmatic Transaction Management
• Spring provides Support for programmatic transaction management by using TransactionTemplate or PlatformTransactionManager implementation.

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