Java并发学习之十一——同步方法

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每个方法声明为synchronized关键字是一个临界区，Java只允许一个对象执行其中的一个临界区。

静态方法有不同的行为。只有一个执行线程访问被synchronized关键字声明的静态方法，但另一个线程可以访问该类的一个对象中的其他非静态的方法。 你必须非常小心这一点，因为两个线程可以访问两个不同的同步方法，如果其中一个是静态的而另一个不是。如果这两种方法改变相同的数据,你将会有数据不一致
的错误。

package chapter2;

public class Account {

private double balance;

public double getBalance() {
return balance;
}

public void setBalance(double balance) {
this.balance = balance;
}

public synchronized void addAmount(double amount){
double tmp = balance;
try {
Thread.sleep(10);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
tmp+=amount;
balance = tmp;
}

public synchronized void subtractAmount(double amount){
double tmp = balance;
try {
Thread.sleep(10);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
tmp-=amount;
balance=tmp;
}

}

package chapter2;

public class Bank implements Runnable{

private Account account;
public Bank(Account account) {
this.account = account;
}

@Override
public void run() {
// TODO Auto-generated method stub
for(int i=0;i<100;i++){
account.subtractAmount(1000);
}
}

}

package chapter2;

public class Company implements Runnable{

private Account account;
public Company(Account account) {
this.account = account;
}

@Override
public void run() {
// TODO Auto-generated method stub
for(int i=0;i<100;i++){
account.addAmount(1000);
}
}

}

package chapter2;

public class Main {

/**
* <p>
* </p>
* @author zhangjunshuai
* @date 2014-9-11 下午4:49:50
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Account account = new Account();
account.setBalance(1000);
Company company = new Company(account);
Thread companyThread = new Thread(company);
Bank bank = new Bank(account);
Thread bankThread = new Thread(bank);
System.out.printf("Account:Initial balance:%f\n", account.getBalance());
companyThread.start();
bankThread.start();
try {
companyThread.join();
bankThread.join();
System.out.printf("Account:Initial balance:%f\n", account.getBalance());
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
}
}

}