使用synchronized同步，经典银行账户问题

1.新建Account类，使用synchronized同步增加和减少金额方法。

package com.xkzhangsan.synchronizedpack.bank;

public class Account {

    private double balance;

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

    public synchronized void substractAmount(double amount){
        double tmp = balance;
        try {
            Thread.sleep(10);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        tmp-=amount;
        balance=tmp;
    }

    public double getBalance() {
        return balance;
    }

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

}

2.新建Company类，往账户增加金额，实现Runnable接口

package com.xkzhangsan.synchronizedpack.bank;

public class Company implements Runnable{

    private Account account;

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

    public void run() {
        for (int i = 0; i < 10; i++) {
            account.addAmount(1000);
            System.out.println("Company add 1000 balance:" + account.getBalance());
        }
    }
}

3.新建Bank类，减少账户金额，实现Runnable接口

package com.xkzhangsan.synchronizedpack.bank;

public class Bank implements Runnable{

    private Account account;

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

    public void run() {
        for (int i = 0; i < 10; i++) {
            account.substractAmount(1000);
            System.out.println("Bank substract 1000 balance:" + account.getBalance());
        }
    }
}

4.新建Main测试类，创建companyThread和bankThread，启动线程，打印账户金额变化

package com.xkzhangsan.synchronizedpack.bank;

public class Main {

    public static void main(String[] args) {
        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 start money:%f\n", account.getBalance());
        companyThread.start();
        bankThread.start();

        try {
            companyThread.join();
            bankThread.join();
            System.out.printf("Account end money:%f\n", account.getBalance());
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

5.测试结果

Account start money:1000.000000
Company add 1000 balance:2000.0
Bank substract 1000 balance:1000.0
Company add 1000 balance:2000.0
Bank substract 1000 balance:1000.0
Company add 1000 balance:2000.0
Bank substract 1000 balance:1000.0
Company add 1000 balance:2000.0
Bank substract 1000 balance:1000.0
Company add 1000 balance:2000.0
Bank substract 1000 balance:1000.0
Company add 1000 balance:2000.0
Bank substract 1000 balance:1000.0
Company add 1000 balance:2000.0
Bank substract 1000 balance:1000.0
Company add 1000 balance:2000.0
Bank substract 1000 balance:1000.0
Company add 1000 balance:2000.0
Bank substract 1000 balance:1000.0
Company add 1000 balance:2000.0
Bank substract 1000 balance:1000.0
Account end money:1000.000000

参考：java7并发编程实战手册

GitHub地址：https://github.com/xkzhangsan/java-concurrent-practice