Abstract class and Interface

 1   Package  Com. Action;  2   3   Public   Interface  Interfacetest {  4   5       Public   Abstract   Void  Fun1 ();  6   7      Void Fun2 (); //  The default values are public and abstract.  8   9       Void  Fun3 ();  10   11       Int I = 10; //  All are public static final by default.  12 }

 1   Package  Com. Action; 2   3   Public   Class Test1 Implements  Interfacetest {  4   5       /**  6   *  @ Param  ARGs  7        */  8       Public  Static   Void  Main (string [] ARGs ){  9           //  Todo auto-generated method stub  10 Test1 test1 = New  Test1 ();  11   Test1.fun1 ();  12   System. Out. println (test1. I );  13   14  }  15   16   @ Override  17       Public   Void  Fun1 (){  18           //  Todo auto-generated method stub  19 System. Out. println ("fun1" );  20   }  21  22   @ Override  23       Public   Void  Fun2 (){  24           //  Todo auto-generated method stub  25 System. Out. println ("fun2" );  26   }  27   28   @ Override 29       Public   Void  Fun3 (){  30           //  Todo auto-generated method stub  31 System. Out. println ("fun3" );  32   }  33   34 }

 1   Package  Com. Action; 2   3   Public   Abstract   Class  Abstractclass {  4   5       Void  Fun1 (){  6 System. Out. println ("fun1" );  7   }  8       Public   Abstract   Void  Fun2 ();  9       10       Public   Int I = 01 ;  11 }

 1   Package  Com. Action;  2   3   Public   Class Test2Extends  Abstractclass {  4   5       /**  6   *  @ Param  ARGs  7        */  8       Public   Static   Void  Main (string [] ARGs ){  9          //  Todo auto-generated method stub  10 Test2 Test2 = New  Test2 ();  11   Test2.fun1 ();  12   Test2.fun2 ();  13 Test2. I = 2 ;  14   System. Out. println (test2. I );  15   } 16   17   @ Override  18       Public   Void  Fun2 (){  19           //  Todo auto-generated method stub  20 System. Out. println ("fun2" );  21   }  22   23 }

 

1. abstract class represents an inheritance relationship in Java. A class can only use an inheritance relationship once. However, a class can implement multiple interfaces.

2. In abstract class
You can have your own data members or non-Abstarct member methods. In the interface, you can only have static data members that cannot be modified (that is, they must be
Static final, but data members are generally not defined in the interface). All member methods are abstract.

3. abstract class and interface have different design concepts. Abstract class represents the "is-a" relation, and interface represents the "like-a" relation.

4. The class implementing the interface must implement all the methods in it, and the class implementing the abstract class must implement the abstract methods in it, rather than the abstract methods. Abstract classes can have non-abstract methods. There is no implementation method in the interface.

5. the variables defined in the interface are of the public static final type by default and must be given the initial values. Therefore, the Implementation class cannot be redefined or changed.

6. the variables in the abstract class are friendly by default. Their values can be redefined in the subclass or assigned again.

7. The methods in the interface are public and abstract by default.