本文介绍Java最基本的同步方式,即使用synchronized关键字来控制一个方法的并发访问,如果一个对象已用synchronized关键字声明,那么只有一个执行线程允许去访问它,其它试图访问这个对象的线程将被挂起,直到第一个线程访问完毕。
下面通过一个小例子来学习这个概念,公司向银行存钱,取钱场景。
1:创建Account的账号类,它是银行账户的模型,只有一个双精度浮点型属性,balance.
2:实现balance的get set 方法。
3:实现AddAmount()方法,将传入的数量加到余额balance中,并且在同一时间只允许一个线程去改变这个值,使用synchronized关键字。
4:实现SubtractAmount()方法,将传入的数量从余额balance中扣除,并且在同一时间只允许一个线程去改变这个值。
具体代码:
public class Account {
/**
* Balance of the bank account
*/
private double balance;
/**
* Returns the balance of the account
* @return the balance of the account
*/
public double getBalance() {
return balance;
}
/**
* Establish the balance of the account
* @param balance the new balance of the account
*/
public void setBalance(double balance) {
this.balance = balance;
}
/**
* Add an import to the balance of the account
* @param amount import to add to the balance
*/
public synchronized void addAmount(double amount) {
double tmp=balance;
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
tmp+=amount;
}
/**
* Subtract an import to the balance of the account
* @param amount import to subtract to the balance
*/
public synchronized void subtractAmount(double amount) {
double tmp=balance;
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
tmp-=amount;
balance=tmp;
}
}
5:实现一个ATM模拟类Bank,它使用subtractAmount()方法对账户的余额进行扣除,实现Runabl接口。
具体代码:
public class Bank implements Runnable {
/**
* The account affected by the operations
*/
private Account account;
/**
* Constructor of the class. Initializes the account
* @param account The account affected by the operations
*/
public Bank(Account account) {
this.account=account;
}
/**
* Core method of the Runnable
*/
public void run() {
for (int i=0; i<100; i++){
account.subtractAmount(1000);
}
}
}
6:实现公司模拟类,调用addAmount()方法进行存钱,实现Runabl接口。
具体代码:
public class Company implements Runnable {
/**
* The account affected by the operations
*/
private Account account;
/**
* Constructor of the class. Initializes the account
* @param account the account affected by the operations
*/
public Company(Account account) {
this.account=account;
}
/**
* Core method of the Runnable
*/
public void run() {
for (int i=0; i<100; i++){
account.addAmount(1000);
}
}
7:在主方法中调用测试:通过线程的join方法,在存期那,取钱线程模拟完毕后打印出结构。
public class Main {