定義

1. 使用interface定義
2. 介面當中的方法都是抽象方法
3. 介面當中的方法都是public許可權

實現

1. 實現介面使用implements關鍵字
2. 一個類可以實現多個介面
3. 一個介面可以繼承多個介面

一個類可以實現多個介面

public interface USB {

    void read();

    void write();
}

public interface WiFi {

    void open();

    void close();
}

public class Phone implements USB, WiFi {

    public Phone() {
        // TODO Auto-generated constructor stub
 

        System.out.println("Phone 無參構造");
    }

    @Override
    public void open() {
        // TODO Auto-generated method stub
        System.out.println("open");
    }

    @Override
    public void close() {
        // TODO Auto-generated method stub
        System.out.println("close");
    }

    @Override
    
 
public void read() {
        // TODO Auto-generated method stub
        System.out.println("read");
    }

    @Override
    public void write() {
        // TODO Auto-generated method stub
        System.out.println("write");
    }

}

public class Test {

    public Test() {
        // TODO Auto-generated constructor stub
 

    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        USB usb = new Phone();
        usb.write();
        usb.read();

        WiFi wiFi = new Phone();
        wiFi.open();
        wiFi.close();
    }

}

執行結果

Phone 無參構造
write
read
Phone 無參構造
open
close

一個介面可以繼承多個介面

public interface PhoneDevice extends USB, WiFi {

    void connect();
    
}

public class Phone implements PhoneDevice {

    public Phone() {
        // TODO Auto-generated constructor stub
        System.out.println("Phone 無參構造");
    }

    @Override
    public void read() {
        // TODO Auto-generated method stub
        System.out.println("read");
    }

    @Override
    public void write() {
        // TODO Auto-generated method stub
        System.out.println("write");
    }

    @Override
    public void open() {
        // TODO Auto-generated method stub
        System.out.println("open");
    }

    @Override
    public void close() {
        // TODO Auto-generated method stub
        System.out.println("close");
    }

    @Override
    public void connect() {
        // TODO Auto-generated method stub
        System.out.println("connect");
    }

}

執行結果

Phone 無參構造
write
read
Phone 無參構造
open
close
Phone 無參構造
connect