线程同步，单例模式【例子】

8-1

（1）同步代码块：

public class Ticket implements Runnable {

//共100票

int ticket = 100;

//定义锁对象

Object lock = new Object();

@Override

public void run() {

//模拟卖票

while(true){

//同步代码块

synchronized (lock){

if (ticket > 0) {

//模拟电影选坐的操作

try {

Thread.sleep(10);

} catch (InterruptedException e) {

e.printStackTrace();

}

System.out.println(Thread.currentThread().getName() + "正在卖票:" + ticket--);

}

}

}

}

}

8-2

（2）同步方法：

public class Ticket implements Runnable {

//共100票

int ticket = 100;

//定义锁对象

Object lock = new Object();

@Override

public void run() {

//模拟卖票

while(true){

//同步方法

method();

}

}

 

//同步方法,锁对象this

public synchronized void method(){

if (ticket > 0) {

//模拟选坐的操作

try {

Thread.sleep(10);

} catch (InterruptedException e) {

e.printStackTrace();

}

System.out.println(Thread.currentThread().getName() + "正在卖票:" + ticket--);

}

}

}

8-3

（3）同步锁

public class Ticket implements Runnable {

//共100票

int ticket = 100;

//创建Lock锁对象

Lock ck = new ReentrantLock();

@Override

public void run() {

//模拟卖票

while(true){

//synchronized (lock){

ck.lock();

if (ticket > 0) {

//模拟选坐的操作

try {

Thread.sleep(10);

} catch (InterruptedException e) {

e.printStackTrace();

}

System.out.println(Thread.currentThread().getName() + "正在卖票:" + ticket--);

}

ck.unlock();

//}

}

}

}

9-1

 

1. public class Singleton {  

2.     private static Singleton instance;  

3.     private Singleton (){}  

4.   

5.     public static Singleton getInstance() {  

6.     if (instance == null) {  

7.         instance = new Singleton();  

8.     }  

9.     return instance;  

10.     }  

11. }  

 

9-2

1. public class Singleton {  

2.     private static Singleton instance;  

3.     private Singleton (){}  

4.     public static synchronized Singleton getInstance() {  

5.     if (instance == null) {  

6.         instance = new Singleton();  

7.     }  

8.     return instance;  

9.     }  

10. }  

 

9-3

1. public class Singleton {  

2.     private static Singleton instance = new Singleton();  

3.     private Singleton (){}  

4.     public static Singleton getInstance() {  

5.     return instance;  

6.     }  

7. }  

 

9-4

1. public class Singleton {  

2.     private Singleton instance = null;  

3.     static {  

4.     instance = new Singleton();  

5.     }  

6.     private Singleton (){}  

7.     public static Singleton getInstance() {  

8.     return this.instance;  

9.     }  

10. }  

 

9-5

1. public class Singleton {  

2.     private static class SingletonHolder {  

3.     private static final Singleton INSTANCE = new Singleton();  

4.     }  

5.     private Singleton (){}  

6.     public static final Singleton getInstance() {  

7.     return SingletonHolder.INSTANCE;  

8.     }  

9. }  

 

9-6

1. public enum Singleton {  

2.     INSTANCE;  

3.     public void whateverMethod() {  

4.     }  

5. }  

 

9-7

1. public class Singleton {  

2.     private volatile static Singleton singleton;  

3.     private Singleton (){}  

4.     public static Singleton getSingleton() {  

5.     if (singleton == null) {  

6.         synchronized (Singleton.class) {  

7.         if (singleton == null) {  

8.             singleton = new Singleton();  

9.         }  

10.         }  

11.     }  

12.     return singleton;  

13.     }  

14. }