定义一个父类 Car

public class Car {

	
	private String name = "汽车";
	private double price=10.0;
	
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public double getPrice() {
		return price;
	}
	public void setPrice(double price) {
		this.price = price;
	}
	public void echo() {
		System.err.println("name:"+name+"price:"+price);
	}
	

 定义一个子类 BMWCar 继承 Car 类

package com.qcbyedu.demo;

public class BMWCar extends Car {
	private String color = "red";
	public String getColor() {
		return color;
	}
	public void setColor(String color) {
		this.color = color;
	}
	
	
	public void echo() {
		// TODO Auto-generated method stub
		System.err.println("name:" + super.getName() + "price:"+super.getPrice()+"color:"+color);
		
	}

}

定义一个Test类：

package com.qcbyedu.demo;

public class Test {

	public static void main(String [] args) {
		
	    	
		Car car = new BMWCar();
		
		Car car1 = new Car();
		
		BMWCar bMWCar = new BMWCar();
		
		car1 = bMWCar;
		
		car.echo();
	
	}
}

此时的 car.echo 将会输出   name:汽车price:10.0color:red

这是因为Car car = new BMWCar(); 实例化的时候在内存申请的空间是存放 name price color 这三个属性的空间 所以子类的属性不会丢失   也就是如上代码  Test中所展现的 

 Car car = new BMWCar(); ===

 Car car1 = new Car();

BMWCar bMWCar = new BMWCar(); 

car1 = bMWCar;
        这三段代码的和