在多线程开发中，总会遇到多个在不同线程中的方法操作同一个数据，这样在不同线程中操作这个数据不同的顺序

或者时机会导致各种不同的现象发生，以至于不能实现你预期的效果，不能实现一致性，这时候就能够使用

synchronizedkeyword对一个方法来说，这个synchronized能保证全部调用这种方法的线程仅仅有一个正在操作这种方法。

不会出现同一时候多个线程进入这种方法的情况，以下我们来一个样例说明这个情况。

首先是一个Account类，这个类模拟账户，提供添加工资和降低工资的方法，当然。这种方法是被synchronized控制

package com.bird.concursey.charpet2;

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

然后是两个模拟类，来模拟使用这个类来添加或者降低账户的剩余金额

package com.bird.concursey.charpet2;

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

	@Override
	public void run() {
		for(int i = 0; i < 100; i++) {
			account.subtractAmount(1000);
		}
	}

}

package com.bird.concursey.charpet2;

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

	@Override
	public void run() {
		for(int i = 0; i < 100; i++) {
			account.addAmount(1000);
		}
	}
	
	
	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 : Initial Balance: %f\n",account.getBalance());
		
		companyThread.start();
		bankThread.start();
		
		
		try {
			companyThread.join();
			bankThread.join();
			System.out.printf("Account : Final Balance: %f\n",account.getBalance());
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
}