Java object-oriented-interface

Java object-oriented- interface

Interface definition: A special kind of "abstract class", there is no ordinary method, which is composed of global constants and public abstract methods;

1, definition of the interface

Interface definition with keyword interface

Let's give the example code:

1  PackageCOM.JAVA1234.CHAP03.SEC12;2  3 /**4 * Define an interface a5  * @authorUser6  *7  */8  Public InterfaceA {9  Ten     /** One * Global Constants A      */ -      Public Static FinalString title= "Hello"; -       the     /** - * Define an abstract method abstraction can be omitted -      */ -      Public Abstract voida (); +}

Note: Because the interface methods are abstract , so abstract can be omitted, the actual development is generally omitted, the habit of developers;

2, implementation interface can implement one or more interfaces

Implement interface We use the Implements keyword , we come up with a test method:

1  PackageCOM.JAVA1234.CHAP03.SEC12;2  3  Public classTestImplementsa{4  5 @Override6      Public voidA () {7System.out.println ("a Method");8     }9  Ten      Public Static voidMain (string[] args) { OneTest t=NewTest (); A t.a (); - System.out.println (test.title); -     } the}

Implement the interface, in the class to implement the abstract method in the interface;

Run output:

A method

Hello

To demonstrate implementing multiple interfaces, we define an interface here:

1  PackageCOM.JAVA1234.CHAP03.SEC12;2  3 /**4 * Define an interface B5  * @authorUser6  *7  */8  Public InterfaceB {9  Ten     /** One * Global Constants A      */ -      Public Static FinalString title2= "Java Knowledge sharing network"; -       the     /** - * Define an abstract method abstraction can be omitted -      */ -      Public Abstract voidb (); +}

We modify the following test class:

1  PackageCOM.JAVA1234.CHAP03.SEC12;2  3  Public classTestImplementsA,  b{4  5 @Override6      Public voidA () {7System.out.println ("a Method");8     }9      Ten @Override One      Public voidB () { ASystem.out.println ("B method")); -     } -   the      Public Static voidMain (string[] args) { -Test t=NewTest (); - t.a (); - t.b (); + System.out.println (test.title); - System.out.println (test.title2); +     } A   at       -}

implement multiple interfaces, separated by commas, and implement all abstract methods :

Run output:

A method

B method

Hello

Java Knowledge sharing Network

3, inheriting classes and implementing interfaces inherit first, then implement interface

Let's first define a class C:

1  Package COM.JAVA1234.CHAP03.SEC12; 2  3  Public class C {4  5      Public void C () {6         System.out.println ("C Method"); 7     }8 }

We then modify the test class tests to inherit the C class, implement a A, A/b interface, here is a note,Java specification, must first inherit the interface after implementation;

Our upper and lower code:

1  PackageCOM.JAVA1234.CHAP03.SEC12;2  3  Public classTestextendsCImplementsa,b{4  5 @Override6      Public voidA () {7System.out.println ("a Method");8     }9      Ten @Override One      Public voidB () { ASystem.out.println ("B method")); -     } -   the      Public Static voidMain (string[] args) { -Test t=NewTest (); - t.a (); - t.b (); + t.c (); - System.out.println (test.title); + System.out.println (test.title2); A     } at   -       -}

Run output:

A method

B method

C method

Hello

Java Knowledge sharing Network

4, interface inheritance interfaces can inherit multiple

We define a D interface to inherit A/b interface :

1  Package COM.JAVA1234.CHAP03.SEC12; 2  3  Public Interface extends a,b{4  5      Public void d (); 6 }

Add a D method here;

We re-engage a test method inherits Class C, implementing the D interface:

1  PackageCOM.JAVA1234.CHAP03.SEC12;2  3  Public classTest2extendsCImplementsd{4  5 @Override6      Public voidA () {7System.out.println ("a Method");8     }9  Ten @Override One      Public voidB () { ASystem.out.println ("B method")); -     } -   the @Override -      Public voidd () { -System.out.println ("D method")); -     } +   -      Public Static voidMain (string[] args) { +Test2 t=NewTest2 (); A t.a (); at t.b (); - t.c (); - t.d (); - System.out.println (test2.title); - System.out.println (test2.title2); -     } in}

Run output:

A method

B method

C method

D method

Hello

Java Knowledge sharing Network

Note:

Interfaces in Java cannot be instantiated.

Java object-oriented-interface