Java--多线程--synchronized--同步
目录
synchronized--同步
练习一
package syn;
//不安全的买票
//线程不安全，有负数
public class UnsafeBuyTicket {
public static void main(String[] args) {
BuyTicket station = new BuyTicket();
new Thread(station,"我").start();
new Thread(station,"你").start();
new Thread(station,"他").start();
}
}
class BuyTicket implements Runnable{
//票
private int ticketNums = 10;
boolean flag = true; //外部停止方式
@Override
public void run() {
//买票
while (flag){
try {
buy();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
//sychronized 同步方法，锁的是this
private synchronized void buy() throws InterruptedException {
//判断是否有票
if (ticketNums<=0){
flag = false;
return;
}
//模拟延时
Thread.sleep(1000);
//买票
System.out.println(Thread.currentThread().getName()+"拿到"+ticketNums--);
}
}
//运行结果-1原因：
//每个线程在自已的工作内存交互，内存控制不当会造成数据不一致
练习二
package syn;
//不安全的取钱
//两个去银行取钱，账户
public class UnsafeBank {
public static void main(String[] args) {
//账户
Account account = new Account(100,"结婚基金");
Drawing you = new Drawing(account,50,"你");
Drawing girlFriend = new Drawing(account,100,"女朋友");
you.start();
girlFriend.start();
}
}
//账户
class Account{
int money; //余额
String name; //卡名
public Account(int money, String name) {
this.money = money;
this.name = name;
}
}
//银行
class Drawing extends Thread{
Account account;//账户
//取了多少钱
int drawingMoney;
//现在手里有多少钱
int nowMoney;
public Drawing(Account account,int drawingMoney,String name){
super(name);
this.account = account;
this.drawingMoney = drawingMoney;
}
//取钱
//synchronized 默认锁的是this
@Override
public void run() {
//锁的对象就是变化的量，需要增删改的对象
synchronized (account){
//判断有没有钱
if (account.money-drawingMoney<0){
System.out.println(Thread.currentThread().getName()+"钱不够，取不了");
return;
}
//sleep可以放大问题的发生性
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
//卡内余额 = 余额 - 你取的钱
account.money = account.money - drawingMoney;
//你手里的钱
nowMoney = nowMoney + drawingMoney;
System.out.println(account.name+"余额为："+account.money);
//Thread.currentThread().getName() = this.getName()
System.out.println(this.getName()+"手里的钱:"+nowMoney);
}
}
}
练习三
package syn;
import java.util.ArrayList;
import java.util.List;
//线程不安全的集合
public class UnsafeList {
public static void main(String[] args) {
List<String> list = new ArrayList<String>();
for (int i = 0; i < 10000; i++) {
new Thread(()->{
synchronized (list){
list.add(Thread.currentThread().getName());
}
}).start();
}
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(list.size());
}
}