Java 介面的用法

最簡單的介面宣告：

public interface EletronicDevice {
    public void turnOn();
    public void turnOff();
}

使用方式：

public class Television implements EletronicDevice{

    @Override
    public void turnOn() {
        System.out.println("電視機開啟中...");
        initializeScreen();
    }

    @Override
    public void turnOff() {
        initializeScreen();
        System.out.println("電視機關閉中...");
    }
    
    public void changeChannel(int channel){
        System.out.printf("切換至第 %d 台", channel);
    }
    
    private void initializeScreen(){
        System.out.println("清除螢幕視窗....");
    }
}

執行方式：

public class Demo {
    public static void main(String[] args){
        
        EletronicDevice ed = new Television();
        ed.turnOn();

        //介面與類別相同的功能：casting
        ((Television)ed).changeChannel(2); 

        ed.turnOff();
        String s = ed.toString();
        System.out.println(s);
    }
}