Summary of usage of implements and extends in Java

1 InterfaceInterfaceone2{3 voidSayHello ();4}5 / * Interface with extends keyword 6 interface Interfacetwo implements Interfaceone 7 { 8 9}*/Ten InterfaceInterfacethreeextendsInterfaceone One{ A} - //Abstract classes can not implement interfaces or methods of parent abstract classes.  - Abstract classAbstractclassoneImplementsInterfaceone the{ -} - Abstract classAbstractclasstwoextendsAbstractclassone -{ +} - //non-abstract classes must implement methods within the interface.  + classClassoneImplementsInterfaceone A{ at  Public voidSayHello () {}; -}

If you encounter a number of methods that need to be implemented in an interface, we only need to use a few of these methods,
Assume that the interface that needs to inherit is:

  1interface A  2 {  3void operation1 ();   4void operation2 ();   5 ...   6void operation100 ();   7 }

Let's say we just need to use one of the OPERATION5
If this interface is inherited directly, all methods are implemented:

1 classClassImplementsA2{3  Public voidOperation1 () {}4  Public voidOperation2 () {}5......6  Public voidOperation5 () {7 /*  8 * OPERATION5 9 * /Ten} One...... A  Public voidOperation100 () {} -}

This is very cumbersome, so you can use the following methods to solve,
Create a new abstract class (if you specify an interface method to be implemented, set it as an abstract method, for example operation99 must be implemented):

1 Abstract classAbstractImplementsA2{3  Public voidOperation1 () {}4  Public voidOperation2 () {}5......6  Public voidOperation98 () {}7 //The operation99 here does not provide a virtual implementation, so it must be implemented in a specific class. 8  Public voidOperation100 () {}9}

To provide a virtual implementation for all interface methods, the future use of this interface only needs to do the following:

1 classClassextendsAbstract2{3 //Rewrite operation54  Public voidOperation5 () {5 /*  6 * operation5 7 * /8}9 //Implement Operation99Ten  Public voidOperation99 () { One /* * operation99  * *   -} the}

This eliminates the need to provide implementations for each interface method.

Summary of usage of implements and extends in Java