what is java interface

1. What is an interface

The interface is a specification, similar to the interface on the hardware, the PCI slot on the computer motherboard The specification is similar to the Java interface. As long as it follows the PCI interface, any brand of card can be inserted into the PCI slot. So the interface is a specification. An interface is a description of some functions provided by something to the outside world. We can also use interfaces to implement polymorphic functions. At the same time, interfaces also make up for the weakness of Java's single inheritance, that is, a class can implement multiple interfaces.

2. What is java interface

Interface (English: Interface) is an abstract type in the JAVA programming language and is a collection of abstract methods. The interface usually starts with interface to declare. A class inherits the abstract methods of the interface by inheriting the interface. (Recommended tutorial: java tutorial)

We use the interface keyword to define the interface , generally use interfaces to declare methods or constants. Methods in interfaces can only be declarations, not specific implementations. This is different from abstract classes. Interfaces are higher level abstractions. The definition format of the interface is

public interface 接口名称{
    //可以定义常量
    //方法只有方法声明,而且是公共的。
    public void 方法名称();
    ...
}

If a class wants to implement the interface, it only needs to use the implements keyword. The implementation class must implement all the methods in the interface

public class 实现类名 implements 接口{
    //实现接口的方法
}

3. Application of interfaces

It is very simple to define an interface. Of course, it is not very simple to design a good interface. You must think about the constants and methods of this interface. But the technology is very simple. The sample code is as follows:

// 定义方法的接口
public interface Myinterface {
  // 定义程序使用的常量的接口，接口中只能有常量。
  public static final double price = 1450.00;
  public static final int counter = 5;
  //接口中所有的方法都没有方法体。
  public void add(int x, int y);
  public void volume(int x,int y, int z);
}

It is not difficult to implement the interface. The code is as follows:

//实现     接口
public class MyImple implements Myinterface {
    @Override
    public void add(int x, int y) {
    }
    @Override
    public void volume(int x, int y, int z) {
    }
}

A class can implement multiple interfaces because Java is single inheritance. The interface can make up for this. We can define another interface

public interface MyInterface2 {
    public void countpp();
}

Modify the above implementation class. To implement multiple interfaces, you can use commas to separate them. Of course, all interface methods must be implemented.

//实现       接口1,接口2
public class MyImple implements Myinterface ,MyInterface2{
    @Override
    public void add(int x, int y) {
    }
    @Override
    public void volume(int x, int y, int z) {
    }
    @Override
    public void countpp() {
    }
}

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