多态override

example one

public class OverrideDemo {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		show(new Cat());
		show(new Dog());
		
		Animal a = new Cat();
		a.eat();
		
		Cat c = (Cat)a;//transition down,,downcasting
		c.work();

	}
	
	public static void show(Animal a){
		a.eat();
		
		if(a instanceof Cat){
			Cat c = (Cat) a;
			c.work();
		}else if(a instanceof Dog){
			Dog c = (Dog) a;
			c.work();
		}
	}

}
abstract class Animal{
	abstract void eat();
}

class Cat extends Animal{
	//override
	public void eat(){
		System.out.println("eat fish");
	}
	
	public void work(){
		System.out.println("Cathching the mouse");
	}
}

class Dog extends Animal{
	//@override
	public void eat(){
		System.out.println("eat bone");
	}
	
	public void work(){
		System.out.println("guarding the house");
	}
}

多态就是同一个接口，使用不同的实例而执行不同操作。

多态性是对象多种表现形式的体现。

public class JavaDemo {

	/**
	 * @param args
	 */
	//来自廖雪峰官方网站
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Income[] incomes = new Income[]{
				new Income(1000),
				new Salary(6000),
				new Lottery(100000)
		};
		System.out.println(totalTax(incomes));
	}
	public static double totalTax(Income... incomes){
		double total = 0;
		for(Income income : incomes){

			total += income.getTax();
		}
		return total;
	}

}

class Income{
	protected double income;
	
	public Income(double income){
		this.income = income;
	}
	
	public double getTax(){
		return income * 0.1;
	}
}

class Salary extends Income{
	//struction method
	public Salary(double income){
		super(income);
	}
	
	//@override
	public double getTax(){
		if(income <= 5000){
			return 0;
		}
		return (income - 5000) * 0.2;
	}
}

class Lottery extends Income{
	public Lottery(double income){
		super(income);
	}
	
	//@override
	public double getTax(){
		return income * 0.4;
	}
}