一.Android Java基礎(chǔ)_多態(tài)性

向上轉(zhuǎn)換:只能定義被子類覆寫的方法，不能調(diào)用在子類中定義的方法。

class Father {
	private int money;	

	public int getMoney() {return money; }
	public void setMoney(int money) {this.money = money; }

	public void printInfo() {System.out.println("This is Father");}

}

class Son extends Father{
	public void printInfo() {System.out.println("This is son");}
	public void playGame() {System.out.println("playGame ...");}
	
}

class Daughter extends Father{
	public void printInfo() {System.out.println("This is daughter");}

	
}

public class Cnv {
	public static void main (String args[]) {
		Son son = new Son();
		Daughter daughter = new Daughter();

		Father f = son; /*  */
		f.printInfo();

		//f.playGame();

		f = daughter;
		f.printInfo();
		
	}
}

運(yùn)行結(jié)果：

root@ubuntu:/home/topeet/guyilian# javac Cnv.java 
root@ubuntu:/home/topeet/guyilian# java Cnv
This is son
This is daughter

JAVA向下轉(zhuǎn)換的例子,在進(jìn)行對(duì)象的向下轉(zhuǎn)換前，必須首先發(fā)生對(duì)象的向上轉(zhuǎn)換.否則會(huì)編譯不過

class Father {
	private int money;	

	public int getMoney() {return money; }
	public void setMoney(int money) {this.money = money; }

	public void printInfo() {System.out.println("This is Father");}

}

class Son extends Father{
	public void printInfo() {System.out.println("This is son");}
	public void playGame() {System.out.println("playGame ...");}
	
}

class Daughter extends Father{
	public void printInfo() {System.out.println("This is daughter");}

	
}

public class Cnv2 {
	public static void main (String args[]) {
		Father f = new Son();
		Son son = (Son)f;   /* Son son = new Son(); */
	}
}

運(yùn)行結(jié)果：

root@ubuntu:/home/topeet/guyilian# javac Cnv2.java 
root@ubuntu:/home/topeet/guyilian# java Cnv2

看一下，下面的例子，假如有一千個(gè)類繼承了father這個(gè)類，如果我們要打印他們的信息，那樣我們豈不是要寫1千個(gè)print函數(shù),下面的第二個(gè)代碼則通過向上轉(zhuǎn)換這個(gè)技巧實(shí)現(xiàn).

class Father {
	private int money;	

	public int getMoney() {return money; }
	public void setMoney(int money) {this.money = money; }

	public void printInfo() {System.out.println("This is Father");}

}

class Son extends Father{
	public void printInfo() {System.out.println("This is son");}
	public void playGame() {System.out.println("playGame ...");}
	
}

class Daughter extends Father{
	public void printInfo() {System.out.println("This is daughter");}

	
}

public class Cnv3 {
	public static void main (String args[]) {
		Father f = new Father();
		Son s = new Son();
		Daughter d = new Daughter();

		print(f);
		print(s);
		print(d);
	}

	public static void print(Father f) {
		f.printInfo();
	}

	public static void print(Son s) {
		s.printInfo();
	}

	public static void print(Daughter d) {
		d.printInfo();
	}
	
}

運(yùn)行結(jié)果：

root@ubuntu:/home/topeet/guyilian# javac Cnv3.java 
root@ubuntu:/home/topeet/guyilian# java Cnv3
This is Father
This is son
This is daughter

通過向上轉(zhuǎn)換實(shí)現(xiàn):

class Father {
	private int money;	

	public int getMoney() {return money; }
	public void setMoney(int money) {this.money = money; }

	public void printInfo() {System.out.println("This is Father");}

}

class Son extends Father{
	public void printInfo() {System.out.println("This is son");}
	public void playGame() {System.out.println("playGame ...");}
	
}

class Daughter extends Father{
	public void printInfo() {System.out.println("This is daughter");}

	
}

public class Cnv4 {
	public static void main (String args[]) {
		Father f = new Father();
		Son s = new Son();
		Daughter d = new Daughter();

		print(f);
		print(s);
		print(d);
	}

	public static void print(Father f) {
		f.printInfo();
	}

	
}

運(yùn)行結(jié)果：

root@ubuntu:/home/topeet/guyilian# javac Cnv4.java 
root@ubuntu:/home/topeet/guyilian# java Cnv4
This is Father
This is son
This is daughter

instanceof: 用來判斷一個(gè)對(duì)象是不是某個(gè)類的實(shí)例

class Father {
	private int money;	

	public int getMoney() {return money; }
	public void setMoney(int money) {this.money = money; }

	public void printInfo() {System.out.println("This is Father");}
	public void drink() {System.out.println("drink ...");}

}

class Son extends Father{
	public void printInfo() {System.out.println("This is son");}
	public void playGame() {System.out.println("playGame ...");}
	
}

class Daughter extends Father{
	public void printInfo() {System.out.println("This is daughter");}
	public void dance() {System.out.println("dance ...");}

	
}

public class Cnv5 {
	public static void main (String args[]) {
		Father f = new Father();
		Son s = new Son();
		Daughter d = new Daughter();

		printAction(f);
		printAction(s);
		printAction(d);
	}

	public static void printAction(Father f) {
		if (f instanceof Son) {
			Son son = (Son)f;
			son.playGame();
		}
		else if (f instanceof Daughter) {
			Daughter d = (Daughter)f;
			d.dance();
		}
		else if (f instanceof Father) {
			f.drink();
		}
	}
}

運(yùn)行結(jié)果：文章來源地址http://www.zghlxwxcb.cn/news/detail-837034.html

root@ubuntu:/home/topeet/guyilian# javac Cnv5.java 
root@ubuntu:/home/topeet/guyilian# java Cnv5
drink ...
playGame ...
dance ...

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