Java面向对象练习

 1 package firstproject;
 2 //定义一个car类
 3 class Car
 4 {
 5     //描述颜色
 6     String color="blue";
 7     //描述轮胎数
 8     int n=4;
 9     //描述行为
10     void run()
11     {
12         System.out.println("The car is running!");
13     }
14 }
15 public class CarDemo 
16 {    
17     public static void main(String[] args)
18     {
19         //实例化车对象
20         Car c=new Car();
21         //修改车的颜色属性
22         c.color="green";
23         System.out.println(c.color);
24         c.run();
25         Car c1=new Car();
26         System.out.println(c1.color);
27         
28         //多个引用，同一个对象
29         Car c2=new Car();
30         Car c3=new Car();
31         c2.color="black";
32         c3=c2;
33         c3.n=5;
34         System.out.println(c2.n);
35     }
36     
37 }

 1 package firstproject;
 2 //定义一个car类
 3 class Car
 4 {
 5     //描述颜色
 6     String color="blue";
 7     //描述轮胎数
 8     int n=4;
 9     //描述行为
10     void run()
11     {
12         System.out.println("The car is running!");
13     }
14 }
15 public class CarDemo 
16 {    
17     public static void main(String[] args)
18     {
19         //对象当作实参
20         Car c=new Car();
21         r(c);
22         //匿名对象当作实参
23         r(new Car());
24     }
25     public static void r(Car c)
26     {
27         c.color="red";
28         c.n=3;
29         c.run();
30     }
31 }