摘自百度

1、介面必須要具體類實現才有意義,所以必須是public
2.、介面中的資料對所有實現類只有一份,所以是static
3、要使實現類為了向上轉型成功,所以必須是final的，比如介面A,A有變數value.實現類A1,A2,可以向上轉型.

interface Singer{
    public int i=0;
    public void sing();
    public void talk();
}

interface SongWriter{
    public int i=1;
    public void write();
    public
 
 void talk();
}

interface Zhoujielun extends Singer, SongWriter{
    int i=2;
    public void sing();
    public void write();
    public default void talk(){
        System.out.println(" zhoujielun talk"+Singer.i+" "+SongWriter.i);
        // i = 3; 這裡會報錯
    }
}

public class InterfaceTest implements
 
 Zhoujielun{
    public static void main(String[] args){
        InterfaceTest ift = new InterfaceTest();
        ift.talk();
    }

    public void sing(){

    }

    public void write(){

    }

}