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The document compares and contrasts abstract classes and interfaces in Java, noting that abstract classes can contain both abstract and non-abstract methods while interfaces only contain abstract methods, and that abstract classes can contain constructors while interfaces cannot. It also discusses the differences between static and non-static inner classes, explaining that non-static inner classes require an enclosing instance while static inner classes do not.
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- 1. 1. Abstract class is a class which contain one or more abstract methods, which has to be implemented by sub classes . Inteface is a Java Object containing method declaration and doesn't contain implementation. The classes which have implementing the Interfaces must provide the method defination for all the methods.2. Abstract class is a Class prefix wtih a abstract keyword followed by Class definaton. Interacace is a Interface which starts with interface keyword.3. Abstract class contatins one or more abstract methods. where as Interface contains all abstract methods and final declarations.4. Abstract class contains the method defination of the some methods. but Interface contains only method declaration, no defination provided.5. Abstract classes are useful in a situation that Some general methods should be implemented and specialization behaviour should be implemented by child classes. Interafaces are useful in a situation that all properties should be implemented we can use this scenario Interface Abstract Class --------------------------------------------------------------------------- (1) Decelear with keyword (1) Decelear with keyword interface Abstract. (2) It will not (2) Itwill may or may contain Constructor. Constructor. (3) By default all methods (3) It may contact Abstract are Public AbstractMethods. methods and non Abstract methods. (4) it will contain only (4) It will final variables and final variables, Instances Variables. 2. There is two defference between static inner and non static inner class. I)In the case of declaring data memeber and member method , non static inner class cannot have static data member and static member method But Static Inner class can have static and non static data member and member method II) In the case of creating instance, the instance of non s static inner class is created with the reference of object of outer class in which it is definedthis means it have inclosing instance . But the instance of static inner class is created with the reference of Outer class, not with the reference of object of outer class..this means it have not inclosing instance For example class A { class B { // static int x; not allowed here.. } static class C { static int x; // allowed here } } class Test { public static void main(String str) { A o=new A(); A.B obj1 =o.new B();//need of inclosing instance A.C obj2 =new A.C(); // not need of reference of object of outer class. } } 3. Java Final Keyword