线程的锁

package xml;import java.util.logging.Level;import java.util.logging.Logger;public class Text { private Integer money; private final Object moneyMutex = new Object(); public Text(){ money = new Integer(0); } public void deposit(int money){ if(money <= 0){ return; } synchronized(this.money){ int result = this.money.intValue() + money; this.money = new Integer(result); this.money.notify(); System.out.println("deposit: " + this.money.intValue()); } } public boolean withdraw(int money){ if(money <= 0){ return false; } synchronized(this.money){ while(this.money.intValue() < money){ try { System.out.println("withdraw to wait: " + this.money.intValue()); this.money.wait(); System.out.println("withdraw out of wait: " + this.money.intValue()); } catch (InterruptedException ex) { Logger.getLogger(Text.class.getName()).log(Level.SEVERE, null, ex); } } int result = this.money.intValue() - money; this.money = new Integer(result); System.out.println("withdraw: " + this.money.intValue()); } return true; } public static void main(String[] args) throws InterruptedException{ Text text = new Text(); new Thread(new Customer(text)).start(); for(int i = 0; i < 6; i++){ text.deposit(333); Thread.sleep(1000); } }}class Customer implements Runnable{ private Text text; public Customer(Text text){ this.text = text; } public void run() { text.withdraw(1000); }} 

这一段代码，运行结果是：

 

withdraw to wait: 333

Exception in thread "main" java.lang.IllegalMonitorStateException

        at java.lang.Object.notify(Native Method)

        at xml.Text.deposit(Text.java:31)

        at xml.Text.main(Text.java:61)

这是由于这一段代码

synchronized(this.money){ int result = this.money.intValue() + money; this.money = new Integer(result); this.money.notify(); System.out.println("deposit: " + this.money.intValue()); } 

对this.money加锁后，我却有改变了this.money的值，又调用this.money.notify();，所以导致该异常。

比较正确的做法是用moneyMutex变量。如下代码：

package xml;import java.util.logging.Level;import java.util.logging.Logger;public class Text { private Integer money; private final Object moneyMutex = new Object(); public Text(){ money = new Integer(0); } public void deposit(int money){ if(money <= 0){ return; } synchronized(this.moneyMutex){ int result = this.money.intValue() + money; this.money = new Integer(result); this.moneyMutex.notify(); System.out.println("deposit: " + this.money.intValue()); } } public boolean withdraw(int money){ if(money <= 0){ return false; } synchronized(this.moneyMutex){ while(this.money.intValue() < money){ try { System.out.println("withdraw to wait: " + this.money.intValue()); this.moneyMutex.wait(); System.out.println("withdraw out of wait: " + this.money.intValue()); } catch (InterruptedException ex) { Logger.getLogger(Text.class.getName()).log(Level.SEVERE, null, ex); } } int result = this.money.intValue() - money; this.money = new Integer(result); System.out.println("withdraw: " + this.money.intValue()); } return true; } public static void main(String[] args) throws InterruptedException{ Text text = new Text(); new Thread(new Customer(text)).start(); for(int i = 0; i < 6; i++){ text.deposit(333); Thread.sleep(1000); } }}class Customer implements Runnable{ private Text text; public Customer(Text text){ this.text = text; } public void run() { text.withdraw(1000); }}