1 package com.jdk7.chapter2.singleton;
2
3 public class SingletonA {
4 //java虚拟机会加载静态变量
5 private static int id = 1
;
6 private static SingletonA instance =
new SingletonA();
7
8 //私有构造函数，不被其他类调用创建类的对象
9 private SingletonA(){}
10
11 //同步获取id值，同一时刻只有一个线程进入该方法
12 public synchronized int getId() {
13 return id;
14 }
15
16 public synchronized int next(){
17 return id++
;
18 }
19 //在其他类中只能调用类名+getInstance方法获取类的对象
20 public static SingletonA getInstance() {
21 return instance;
22 };
23 }
1 package com.jdk7.chapter2.singleton;
2
3 public class SingletonB {
4 //java虚拟机会加载静态变量
5 private static int id = 1
;
6 private static SingletonB instance =
null;
7
8 //私有构造函数，不被其他类调用创建类的对象
9 private SingletonB(){}
10
11 //同步获取id值，同一时刻只有一个线程进入该方法
12 public synchronized int getId() {
13 return id;
14 }
15
16 public synchronized int next(){
17 return id++
;
18 }
19
20 //只创建一次对象，提供给后面每次使用
21 public static SingletonB getInstance() {
22 if(instance==
null){
23 instance =
new SingletonB();
24 }
25 return instance;
26 }
27 }
1 package com.jdk7.chapter2.singleton;
2
3 public class SingleTest {
4 public static void main(String[] args) {
5 System.out.println("调用next方法前"
);
6 SingletonA single1 =
SingletonA.getInstance();
7 SingletonA single2 =
SingletonA.getInstance();
8 System.out.println("single1: "+
single1);
9 System.out.println("single2: "+
single2);
10 System.out.println("single1: "+
single1.getId());
11 System.out.println("single2: "+
single2.getId());
12 single1.next();
13 System.out.println("调用next方法后"
);
14 System.out.println("single1: "+
single1.getId());
15 System.out.println("single2: "+
single2.getId());
16
17 SingletonB b1 =
SingletonB.getInstance();
18 SingletonB b2 =
SingletonB.getInstance();
19 System.out.println("调用next方法前"
);
20 System.out.println("b1: "+
b1);
21 System.out.println("b2: "+
b2);
22 System.out.println("b1: "+
b1.getId());
23 System.out.println("b2: "+
b2.getId());
24 System.out.println("调用next方法后"
);
25 b1.next();
26 System.out.println("b1: "+
b1.getId());
27 System.out.println("b2: "+
b2.getId());
28 }
29 }
30
31 执行结果：
32 调用next方法前
33 single1: com.jdk7.chapter2.singleton.SingletonA@64b6be69
34 single2: com.jdk7.chapter2.singleton.SingletonA@64b6be69
35 single1: 1
36 single2: 1
37 调用next方法后
38 single1: 2
39 single2: 2
40 调用next方法前
41 b1: com.jdk7.chapter2.singleton.SingletonB@32728d
42 b2: com.jdk7.chapter2.singleton.SingletonB@32728d
43 b1: 1
44 b2: 1
45 调用next方法后
46 b1: 2
47 b2: 2
1 package com.jdk7.chapter5;
2
3 public class Single {
4 //私有的静态对象
5 private static Single Instance =
new Single();
6
7 //私有的无参构造函数,在该类中可以new对象，但是在其他类中不可以new对象，保证了对象的唯一性
8 private Single(){}
9
10 //仅对外开放Instance变量的getter方法
11 public static Single getInstance() {
12 return Instance;
13 }
14
15 public static void main(String[] args) {
16 Single s =
new Single();
17 System.out.println("s.hashcode>"+
s.hashCode());
18 System.out.println(Single.getInstance());
19 System.out.println(Single.getInstance());
20 }
21 }
22
23 执行结果：
24 s.hashcode>672568948
25 com.jdk7.chapter5.Single@62efae3b
26 com.jdk7.chapter5.Single@62efae3b
转载于:https://www.cnblogs.com/celine/p/8297276.html
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