java继承分析

 1 class Mem
 2 {
 3     public int i;
 4     public Mem(int i)
 5     {
 6         this.i = i;
 7         System.out.println("create Mem: " + i);
 8     }
 9 }
10 class A
11 {
12     public Mem mem = new Mem(9);
13     
14     public A()
15     {
16         System.out.println("-------------------------");
17         System.out.println("create A");
18         System.out.println(this + "  " + this.mem + "  " + this.mem.i);
19         mem = new Mem(99);
20         System.out.println(this + "  " + this.mem + "  " + this.mem.i);
21         change();
22         System.out.println("-------------------------");
23     }
24     public void change()
25     {
26         mem = new Mem(77);
27     }
28 }
29 class B extends A
30 {
31     public B()
32     {
33         System.out.println("**************************************");
34         System.out.println("create B");
35         System.out.println(this + "  " + this.mem + "  " + this.mem.i);
36         super.change();
37         System.out.println(this + "  " + this.mem + "  " + this.mem.i);
38         System.out.println("      " + Integer.toHexString(super.hashCode()) + "  " + super.mem + "  " + super.mem.i);
39         System.out.println("**************************************");
40     }
41     public void change()
42     {
43         mem = new Mem(88);
44     }
45 }
46 public class Test
47 {
48     public static void main(String[] args)
49     {
50         new B();        
51     }
52 }
53 
54 /*output:s
55 
56 create Mem: 9
57 -------------------------
58 create A
59 org.tone.B@15db9742  org.tone.Mem@6d06d69c  9
60 create Mem: 99
61 org.tone.B@15db9742  org.tone.Mem@7852e922  99
62 create Mem: 88
63 -------------------------
64 **************************************
65 create B
66 org.tone.B@15db9742  org.tone.Mem@4e25154f  88
67 create Mem: 77
68 org.tone.B@15db9742  org.tone.Mem@70dea4e  77
69       15db9742  org.tone.Mem@70dea4e  77
70 **************************************
71 
72  */

 1 package org.tone;
 2 
 3 class Mem
 4 {
 5     public int i;
 6     public Mem(int i)
 7     {
 8         this.i = i;
 9         System.out.println("create Mem: " + i);
10     }
11 }
12 class A
13 {
14     public Mem mem = new Mem(9);
15     
16     public A()
17     {
18         System.out.println("-------------------------");
19         System.out.println("create A");
20         System.out.println(this + "  " + this.mem + "  " + this.mem.i);
21         mem = new Mem(99);
22         System.out.println(this + "  " + this.mem + "  " + this.mem.i);
23         change();
24         System.out.println("-------------------------");
25     }
26     public void change()
27     {
28         mem = new Mem(77);
29     }
30 }
31 class B extends A
32 {
33 //  此处定义mem没有初始化，可以在父类构造函数中初始化该变量， 如果在此处或者B类构造方法中初始化了， 则会覆盖父类构造中的初始化;
34 //  此处定义的mem与父类中定义的mem都同时存在于B类中， 其实B类中的super和this指向的是同一个对象(他们的hashcode值是一样的)， 
35 //  只是如果类属性或方法重名的话，通过他们访问属性时，他们会分别找到不同类中定义的属性或方法
36     public Mem mem; 
37     public B()
38     {
39         System.out.println("**************************************");
40         System.out.println("create B");
41         System.out.println(this + "  " + this.mem + "  " + this.mem.i);
42         super.change();
43         System.out.println(this + "  " + this.mem + "  " + this.mem.i);
44         System.out.println("      " + Integer.toHexString(super.hashCode()) + "  " + super.mem + "  " + super.mem.i);
45         System.out.println("**************************************");
46     }
47     public void change()
48     {
49         mem = new Mem(88);
50     }
51 }
52 public class Test
53 {
54     public static void main(String[] args)
55     {
56         new B();        
57     }
58 }
59 
60 /*output:s
61 
62 create Mem: 9
63 -------------------------
64 create A
65 org.tone.B@15db9742  org.tone.Mem@6d06d69c  9
66 create Mem: 99
67 org.tone.B@15db9742  org.tone.Mem@7852e922  99
68 create Mem: 88
69 -------------------------
70 **************************************
71 create B
72 org.tone.B@15db9742  org.tone.Mem@4e25154f  88
73 create Mem: 77
74 org.tone.B@15db9742  org.tone.Mem@4e25154f  88
75       15db9742  org.tone.Mem@70dea4e  77
76 **************************************
77 
78 **************************************
79 
80  */