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.
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