Learn Java: 2017

Thursday, 19 October 2017

java 8 introduction

Unknown 06:47 0

1. What's New in JDK 8

a. Lambda Expressions

b. Functional Interfaces

c. Default methods

d. Static Methods

e. Method Reference and Constructor reference using double column operator(::)

f. Stream API

g. Date and Time API(Joda API)

2. Purpose of Java 8

a. To simplify programming

i. Less code

ii. Maintainable

iii. Readable

b. To get the benefits of the functional program in java, Java uses lambda expressions.

c. To enable parallel processing

3. Lambda expressions

a. Lambda expressions are methods which are do not belong to a class. They are just functions exist in isolation and that function can be treated as values.

b. Functions as Values

i. Normally, We can assign a string or any objects into a variable.

ii. Lambda expression is a method which has assigned to a variable. If we are assigning we do not need other method signature. So the lambda expression signature will be like below code,

aVariable = ()-> {System.out.println("HIIII");}

iii. Lambada expressions with parameters.

lambdaWithParamater = (int x)->{x= x+}

c. Steps to create Lambda Expression Java

i. Create an Interface with abstract method having the same signature of the lambda function and use it as the type for lambda expression variable. This interface must have only one method.

ii. To run this action, call method in the interface.

iii. Its just like implementation of singe function.

public interface LambdaType {

void foo();

public static void main(String[] args) {

LambdaType myLambmadaVoidNoParam = ()->{System.out.println("HIII");};

myLambmadaVoidNoParam.foo();

}

d. Lambda Examples

e. Why lambda expressions ?

i. We are using lambda expression to enable functional programming in java.

ii. To write more readable, maintainable and clean less code.

iii. To use apis very easily effectively.

iv. To enable processing also

4. Function Interface

a. Java.util.function has special interface like bleow, it contains generic methods used as type for lambda expression wirh same type and signature.

i. Predecate Interface

1. It is already having boolean method. So whenever we need a lambda expression with Boolean return type use Predicate as type. No nned to create another interface.

2. Lot of other interfaces available like this.

5. Streams

List.stream().filter(student->getName().startWith(“C”)).foreach(p->System.out.println(p.getName())).

a. Stream consists of 3 main elements

i. Source

1. Collection

ii. Operations

1. Filter(), used to give condition

iii. end operations

1. count()

b. More succinct code, sometimes just one liner

c. You can pass lambda expression, which gives you the immense flexibility to change what you do in the loop.

d. .parallel() can be used for parallel operations.

e. ForEach looping can be made parallel with minimal effort e.g. without writing a single line of concurrent code, all you need to do is call parallelStream() method.

f. forEach() method is defined at two places, on Iterable interface as well as on Stream class. which means list.forEach() and list.stream.forEach() both are valid.

g. Prefer using forEach() with streams because streams are lazy and not evaluated until a terminal operation is called.

h. forEach() is a terminal operation, you cannot call any method on stream after this.

i. When you run forEach() method on parallel stream the order on which elements are processed is not guaranteed, though you can use forEachOrdered() to impose ordering.

j. forEach() method accepts a Consumer instance, which is a functional interface, that's why you can pass a lambda expression to it.

6. PUT vs POST

a. PUT implies putting a resource - completely replacing whatever is available at the given URL with a different thing. By definition, a PUT is idempotent. Do it as many times as you like, and the result is the same. x=5 is idempotent. You can PUT a resource whether it previously exists, or not (eg, to Create, or to Update)!

b. POST updates a resource, adds a subsidiary resource, or causes a change. A POST is not idempotent, in the way that x++ is not idempotent.

c. PATCH: Submits a partial modification to a resource. If you only need to update one field for the resource, you may want to use the PATCH method.

7. JBOSS deployment

a. JBoss AS 7: Copy the .war file to JBOSS_HOME/standalone/deployments.

b. Actually, for the latest JBOSS 7 AS, we need a .deeploy marker even for archives. So add a marker to trigger the deployment.

c. To start server:

> cd bin

> standalone.bat

start tomcat

cd bin

startup.bat

8. 1.6 to 1.8 migration

a. upgraded from Java 6 to Java 8, to benefit from improvements in speed, brevity of code, and lower memory usage.

b. The JDK is backwards compatible, meaning that JDK 8 can run binaries produced by JDK 7 and JDK 6. The javac compiler can also produce binaries targeting earlier versions of the JDK. In planning to upgrade, we will use this capability.

c. When upgrading infrastructure, it is important to segment the architecture. Rather than upgrading everything at the same time, separate it into different environments so that you can test each one on its own.

d. Environment Variables for installation

i. PATH – identifies which actual java executable your system will use when you call java. You can circumvent this by explicitly calling the executable via /opt/jdk8/bin/java or /opt/jdk7/bin/java commands. Just call the one you want to use at the time. If you use scripts that rely on environment variables, consider isolating your terminals if you change the environment.

ii. JAVA_HOME – some applications use this variable to identify where Java is.

iii. Test your upgrade the following commands:

1. java -version

2. This should reply back with 1.8 or 1.7 depending on which you want. Just make sure it is right

3. echo $JAVA_HOME

Thursday, 21 September 2017

Java Algorithms Trees

Unknown 02:04 0

A tree will have a root node on its top and it has child and child have child.
Node with out child are called leaf.
A Binary Tree contains nodes with two children always.Each node has left node and right node.
Binary search tree is a binary tree having specific ordering. Here always left node contains lesser and right node contains higher values. This ordering will make finding a node very fast.
Insertion: There are two types of insertion are there Balanced and Unbalanced

Balanced Insertion

Inserts on next free child based on left right order and time complexity will be lesser here.

Unbalanced Insertion

insert go deep of list and time complexity is higher.

Traversing

In-order Traverse

Visit left node first then root node and then right node

Pre-order

Visit root node first then left node and right node.

Post-Order

Visit left node first then right node and last root node.

Code approach

For Insert

Compare value with root value.
If value lesser or equal to root value then go to left child node. Put value in child node if child node is null.
If child node not null then pass the value to insert method of child.
If value is greater than root node value then do the same with right node.

For Contains

Check node value equals to value.
If equals then return true.
Else if value lesser than root value then go to left. If left node is null return false else call contains method of left node.
Else if value greater than root node value then go to right node and do the same there.


 public class Node {
  int data;
  Node left;
  Node right;

  public Node(int data) {
    this.data = data;
  }

  public void insert(int value) {
    if (value <= data) {
      // inserting if left node is free
      if (left == null) {
        left = new Node(value);
      } else {
        // forward to next node if left node aleady occupied.
        left.insert(value);
      }
    } else {
      if (right == null) {
        right = new Node(value);
      } else {
        right.insert(value);
      }
    }
  }

  public boolean contains(int value) {
    if (data == value) {
      return true;
    } else if (value < data) {
      if (left == null) {
        return false;
      } else {
        left.contains(value);
      }
    } else {
      if (right == null) {
        return false;
      } else {
        right.contains(value);
      }
    }
    return false;
  }

  public void inOrderPrinting() {
    if (left != null) {
      left.inOrderPrinting();
    }
    System.out.println(data);
    if (right != null) {
      right.inOrderPrinting();
    }
  }
}

Reference Link https://www.youtube.com/watch?v=oSWTXtMglKE

Wednesday, 20 September 2017

Java Algorithms Bubble Sort

Unknown 20:13 0

Bubble Sort is the simplest sorting algorithm that works by repeatedly swapping the adjacent elements if they are in wrong order.
Getting each element one by one and comparing it with adjacent elements and swapping the positions.


  public void bubbleSort() {
    int temp, firstValue, secondValue;
    int[] arr = { 1, 90, 25, 22, 4, 50 };
    printArray(arr);
    for (int i = 0; i < arr.length; i++) {
      // #arr.length - 2 -- avoids next index of last index -- secondValue
      for (int j = 0; j < arr.length - 2; j++) {
        firstValue = arr[j];
        secondValue = arr[j + 1];
        if ((firstValue > secondValue)) {
          temp = firstValue;
          arr[j] = secondValue;
          arr[j + 1] = temp;
        }
      }
    }
    System.out.println("-----SORTING DONE-----");
    printArray(arr);
  }

Reference Link https://www.youtube.com/watch?v=T8ErAYobcbc matrix

Java Algorithms Linear Search

Unknown 20:04 0

A linear search traverse down a list, one item at a time, without jumping.


public String linearSearchForValue(int value) {
    String indexesWithValue = "";
    for (int i = 0; i < size; i++) {
      if (theArray[i] == value) {
        indexesWithValue += i + " ,";
      }
    }
    return indexesWithValue;
  }

Travesrse Matrix Diagonally in Java

Unknown 14:57 0

A matrix will be in M x N format.So what we need to do is, get value of indexes from 0,0 to M,N. Itreate the two dimensional array in diagonally as follow


50 36 22  
31 88 87  
27 73 95

After diagonal traverse the output will be.

Consider the above output


50
31 36
27 88 22

These elements start from left to right top
Need to iterate for 0 to M-1 using for loop and display corresponding elements diagonally using a while loop.
To find next element use for formula: M-1,N+1 in while loop


73 87
95

These elements start from bottom to right top
Need to Iterate form 1 to N-1 in for loop and display corresponding elements diagonally using a while loop.
So to find next element use for formula, M-1,N+1 in while loop

TraveseMatrixDiagonally.java


public class TraveseMatrixDiagonally {
 private static final int M = 4;
 private static final int N = 4;
 public static void main(String[] args) {
  TraveseMatrixDiagonally app = new TraveseMatrixDiagonally();
  int[][] matrix = app.createMatrix();
  app.printMatrix(matrix);
  app.traverseDiagonally(matrix);
 }
 private void traverseDiagonally(int[][] matrix) {
  for (int i = 0; i <= M - 1; i++) {
   int X = i; // temp M
   int Y = 0; // temp N
   while (X >= 0 && Y <= N - 1) {
    System.out.print(matrix[X][Y] + " ");
    X = X - 1;
    Y = Y + 1;
   }
   System.out.println(" ");
  }
  for (int i = 1; i <= N - 1; i++) {
   int X = M - 1;
   int Y = i;
   while (X >= 0 && Y <= N - 1) {
    System.out.print(matrix[X][Y] + " ");
    X = X - 1;
    Y = Y + 1;
   }
   System.out.println(" ");
  }
 }
 private int[][] createMatrix() {
  int matrix[][] = new int[M][N];
  for (int i = 0; i < M; i++) {
   for (int j = 0; j < N; j++) {
    matrix[i][j] = (int) ((Math.random() * (99 + 1 - 10)) + 10);
   }
  }
  return matrix;
 }
 private void printMatrix(int[][] matrix) {
  for (int i = 0; i < M; i++) {
   for (int j = 0; j < N; j++) {
    System.out.print(matrix[i][j]);
    System.out.print(" ");
   }
   System.out.println(" ");
  }
 }
}

/*
****** SAMPLE INPUT ********
61 44 88  
74 44 32  
86 56 92 
******* INPUT ********
****** SAMPLE OUTPUT ********
61  
74 44  
86 44 88  
56 32  
92
******* OUTPUT ********
*/

Reference Link https://www.youtube.com/watch?v=T8ErAYobcbc

Tuesday, 19 September 2017

Traverse the matrix as spiral in Java

Unknown 21:35 0

A matrix will be in M x N format.So what we need to do is, get value of indexes from 0,0 to m,n. Itreate the two dimensional array in spiral mode as follow

we need to traverse matrix and remove the row/column which already traversed.
We are not going to delete the elements instead we will limit it by defining boundaries.
Boundaries can be t, b, l, r we need to specify the direction variable dir. It decides the direction of traverse as below.

TraverseMatrixSpiral.java


package com.sk.iwq.matrix;

public class TraverseMatrixSpiral {
 private static final int M = 3;
 private static final int N = 3;

 public static void main(String[] args) {
  TraverseMatrixSpiral app = new TraverseMatrixSpiral();
  int matrix[][] = app.createMatrix();
  app.printMatrix(matrix);
  System.out.println(app.traverseSpriral(matrix).toString());
 }

 private StringBuilder traverseSpriral(int[][] matrix) {  
  StringBuilder sb = new StringBuilder();
  int dir = 0;
  int t = 0;
  int b = M - 1;
  int l = 0;
  int r = N - 1;
  while (t <= b && l <= r) {
   if (dir == 0) {
    for (int i = l; i <= r; i++) {
     sb.append(matrix[t][i] + ", ");
    }
    t++;
   }
   if (dir == 1) {
    for (int i = t; i <= b; i++) {
     sb.append(matrix[i][r] + ", ");
    }
    r--;
   }
   if (dir == 2) {
    for (int i = r; i >= l; i--) {
     sb.append(matrix[b][i] + ", ");
    }
    b--;
   }
   if (dir == 3) {
    for (int i = b; i <= t; i++) {
     sb.append(matrix[i][l] + ", ");
    }
    l++;
   }
   dir = (dir + 1) % 4;
  }
  return sb;
 }

 private int[][] createMatrix() {
  int matrix[][] = new int[M][N];
  for (int i = 0; i < M; i++) {
   for (int j = 0; j < N; j++) {
    matrix[i][j] = (int) (Math.random() * 100 + 1);
   }
  }
  return matrix;
 }

 private void printMatrix(int[][] matrix) {
  for (int i = 0; i < M; i++) {
   for (int j = 0; j < N; j++) {
    System.out.print(matrix[i][j]);
    System.out.print(" ");
   }
   System.out.println(" ");
  }

 }
}

/*
****** SAMPLE INPUT ********
50 36 22  
31 88 87  
27 73 95
******* INPUT ********
****** SAMPLE OUTPUT ********
50, 36, 22, 87, 95, 73, 27, 31, 88
******* OUTPUT ********
*/

Monday, 18 September 2017

Traverse the matrix in Java

Unknown 16:41 0

Traverse the matrix in Java

A matrix will be in M x N format.
So what we need to do is, get value of indexes from 0,0 to m,n.
Itreate the two dimensional array as follow

take 0(i) and traverse j till j < N
take 1(i) and traverse j till j < N
.
.
till M(i) and traverse j till j < N

PrimeNumberCheck.java


public class TraverseMatrix {
 private static final int M = 3;
 private static final int N = 3;
 public static void main(String[] args) {
  TraverseMatrix app = new TraverseMatrix();
  int matrix[][] = app.createMatrix();
  app.printMatrix(matrix);
  app.normalTraverse(matrix);
 } 
 private void normalTraverse(int[][] matrix) {
  for (int i = 0; i < M; i++) {
   for (int j = 0; j < N; j++) {
    System.out.print(matrix[i][j]);
    System.out.print(", ");
   }
  }
 }
 private int[][] createMatrix() {
  int matrix[][] = new int[M][N];
  for (int i = 0; i < M; i++) {
   for (int j = 0; j < N; j++) {
    matrix[i][j] = (int) (Math.random() * 100 + 1);
   }
  }
  return matrix;
 } 
 private void printMatrix(int[][] matrix) {
  for (int i = 0; i < M; i++) {
   for (int j = 0; j < N; j++) {
    System.out.print(matrix[i][j]);
    System.out.print(" ");
   }
   System.out.println(" ");
  }
 }
}

Check number is prime or not

Unknown 15:55 0

To check the given number is prime or not.
Prime Numbers:

A prime number (or a prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself.
It means the remainder of divison of N with numbers from 2 to N/2 should be grater than zero.

Lets take 6 6%2=0, 6%3=0...from 2 to 3(2 to 6/2)
here remainder is zero. So 6 is not prime number.
Lets take 5 now
5%2=1
here remainder is greater than zero. So 5 is prime number.

PrimeNumberCheck.java


public class PrimeNumberCheck {
 public static void main(String[] args) {
  PrimeNumberCheck app = new PrimeNumberCheck();
  System.out.println("Eneter number:");
  Scanner scanner = new Scanner(System.in);
  int number = scanner.nextInt();
  System.out.println(app.isPrime(number));
 }
 private boolean isPrime(int number) {
  boolean isPrime = true;
  for (int i = 2; i <= number / 2; i++) {
   if (number % i == 0) {
    return false;
   }
  }
  return isPrime;
 }
}

/*
****** INPUT ********
5
******* INPUT ********
****** OUTPUT ********
true
******* OUTPUT ********
*/

Friday, 15 September 2017

Order of Execution in java Inheritance

Unknown 21:53 0

Order of Execution

Parent Static Block
Child Static Block
Parent Normal Block
Parent Constructor
Child Normal Block
Child Constructor
Child method invoked

Animal.java

public class Animal { static { System.out.println("Animal Static Block "); } public Animal() { System.out.println("Animal Consuctor"); } { System.out.println("Animal Normal Block"); } public void aboutMe() { System.out.println("I am a Animal"); } }

Cow.java

public class Cow extends Animal { static { System.out.println("Cow Static Block "); } public Cow() { System.out.println("Cow Consuctor"); } { System.out.println("Cow Normal Block"); } public void aboutMe() { System.out.println("I am a Cow"); } }

App.java

public class App { public static void main(String[] args) { Cow cow = new Cow(); cow.aboutMe(); } }

Java Spring Interview Questions

Unknown 21:27 0

Load application Context on Spring?

ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext.xml");
Autowired

@Autowired
private ApplicationContext appContext;

Spring bean scopes: session and globalSession

GlobalSession is something which is connected to Portlet applications. When your application works in Portlet container it is built of some amount of portlets. Each portlet has its own session, but if your want to store variables global for all portlets in your application than you should store them in globalSession. This scope doesn't have any special effect different from session scope in Servlet based applications.

What is the difference between a portlet and a servlet?

Portlets are part of JSR-168 standard that regulates portal containers and components. This is different standard from standards for web containers (and servlets). Though there are definitely strong parallels between these two standards they differ in containers, APIs, life cycle, configuration, deployment, etc.
The main difference between portlet vs. servlet could be that while servlet always responds to single type of action - request, portlet (due to nature of its life cycle and stronger container bindings) has to respond to two types of actions: render and request. There are of course more to it but I found this as the core difference between the two when I studied portal development.

Difference between spring @Controller and @RestController annotation?

@Controller

@Controller is used to mark classes as Spring MVC Controller.
If we need to return values as JSON or XML then need to add @ResponseBody annotation above the method

@RestController

Its methods will automatically converte the response to JSON or XML. No need to add @ResponseBody annotation.


@Controller
@ResponseBody
public class MyController { }

@RestController
public class MyRestController { }

Write a code to create deadlock in java

Unknown 21:12 0


public class DeadLockEx {
  private String str1 = "SPRING";
  private String str2 = "HIBERNATE";

  public static void main(String[] args) {
    DeadLockEx app = new DeadLockEx();
    app.t1.start();
    app.t2.start();
  }

  Thread t1 = new Thread("Thead 1") {
    public void run() {
      while (true) {
        synchronized (str1) {
          synchronized (str2) {
            System.out.println(str1 + str2);
          }
        }
      }
    }
  };
  Thread t2 = new Thread("Thead 2") {
    public void run() {
      while (true) {
        synchronized (str2) {
          synchronized (str1) {
            System.out.println(str2 + str1);
          }
        }
      }
    }
  };

}

Java Oops Interview Questions

Unknown 20:43 0

Implementing two interfaces in a class with same method. Which interface method is overridden?


interface A{
  int f();
}

interface B{
  int f();
}

class Test implements A, B{   
  public static void main(String... args) throws Exception{   

  }

  @Override
  public int f() {  // from which interface A or B
    return 0;
  }
}

If a type implements two interfaces, and each interface define a method that has identical signature, then in effect there is only one method, and they are not distinguishable.
If, say, the two methods have conflicting return types, then it will be a compilation error. This is the general rule of inheritance
This is the general rule of inheritance, method overriding, hiding, and declarations, and applies also to possible conflicts not only between 2 inherited interface methods, but also an interface and a super class method, or even just conflicts due to type erasure of generics.
Reference

Tuesday, 12 September 2017

Two Sum on arrays

Unknown 11:50 0

Given an array of integers, return indices of the two numbers such that they add up to a specific target.
Example:
Given nums = [ 3, 4, 5, 2, 10, 8, 9 ]
target = 19
Because nums[4] + nums[6] = 10 + 9 = 19, return [4, 6]
Approach:
step1. take 3 and then add 3 with all other elements
step2. take 4 and then add 4 with all other elements.Continue same till 9

TwoSum.java


public class TwoSum { 
 public static void main(String[] args) {
  int[] arr = { 3, 4, 5, 2, 10, 8, 9 };
  int target = 19;
  TwoSum app = new TwoSum();
  int[] rslt = app.twosum(arr, target);
  System.out.print(rslt[0] + ", " + rslt[1]);
 }

 private int[] twosum(int[] arr, int target) {
  int[] rslt = new int[2];
  // take 3 and then add 3 with all other
  // take 4 and then add 4 with all other elemnts.Continue same till 9

  for (int i = 0; i < arr.length; i++) {
   for (int j = 0; j < arr.length; j++) {
    if (j != i) { // don't add the same indexes
     int sum = arr[i] + arr[j];
     if (sum == target) {
      rslt[0] = i;
      rslt[1] = j;
      break;
     }
    }

   }
  }
  return rslt;
 }

}

/*
****** INPUT ********
{ 3, 4, 5, 2, 10, 8, 9 }
19
******* INPUT ********
****** OUTPUT ********
4, 6
******* OUTPUT ********
*/

Thursday, 19 October 2017

java 8 introduction

Thursday, 21 September 2017

Java Algorithms Trees

Wednesday, 20 September 2017

Java Algorithms Bubble Sort

Java Algorithms Linear Search

Travesrse Matrix Diagonally in Java

Tuesday, 19 September 2017

Traverse the matrix as spiral in Java

Monday, 18 September 2017

Traverse the matrix in Java

Check number is prime or not

Friday, 15 September 2017

Order of Execution in java Inheritance

Java Spring Interview Questions

Write a code to create deadlock in java

Java Oops Interview Questions

Tuesday, 12 September 2017

Two Sum on arrays

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