synchronized方法和synchronized块
synchronized方法必须获得对象的锁才能执行，否则线程阻塞，方法一旦执行，就独占此锁，直到方法返回才释放锁，后面被阻塞的线程才能获得这个锁，继续执行
synchronized会影响效率
同步块synchronized(Obj){}，Obj是同步监听器，第一个线程访问，所定Obj，完后解锁Obj，第二个才能访问
同步方法弊端：方法里面需要修改的内容才需要锁，锁的太多，浪费资源
package com.wuming.syn.synch;
//不安全的买票
public class UnSafeBuyTicket {
public static void main(String[] args) {
BuyTicket station = new BuyTicket();
new Thread(station,"苦逼的我").start();
new Thread(station,"牛逼的你们").start();
new Thread(station,"可恶的黄牛党").start();
}
}
class BuyTicket implements Runnable{
//票
private int ticketNums=10;
boolean flag=true;//停止方式
/**
* When an object implementing interface <code>Runnable</code> is used
* to create a thread, starting the thread causes the object's
* <code>run</code> method to be called in that separately executing
* thread.
* <p>
* The general contract of the method <code>run</code> is that it may
* take any action whatsoever.
*
* @see Thread#run()
*/
@Override
public void run() {
//买票
while(flag){
try {
buy();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
//synchronized同步方法，锁的是this BuyTicket
private synchronized void buy() throws InterruptedException {
//判断是否有票
if (ticketNums<=0){
flag=false;
return;
}
//模拟延时
Thread.sleep(100);
//买票
System.out.println(Thread.currentThread().getName()+"拿到"+ticketNums--);
//加了synchronized，安全
/* 苦逼的我拿到10
可恶的黄牛党拿到9
可恶的黄牛党拿到8
牛逼的你们拿到7
可恶的黄牛党拿到6
苦逼的我拿到5
苦逼的我拿到4
可恶的黄牛党拿到3
牛逼的你们拿到2
可恶的黄牛党拿到1*/
}
}
===============
package com.wuming.syn;
//不安全的取钱
//两个人去银行取钱，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,"girlFriend");
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，模拟取款
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);//线程name
this.account = account;
this.drawingMoney = drawingMoney;
this.nowMoney = nowMoney;
}
//取钱
//synchronized默认锁的是本身
@Override
public void run() {
//锁的对象是变化的量，增删改;改成this就是指银行，线程不安全如下
/* 结婚基金余额为：-50
结婚基金余额为：-50
你手里的钱50
girlFriend手里的钱100*/
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);
}
//使用同步块 synchronized (account)，线程安全
/* 结婚基金余额为：50
你手里的钱50
girlFriend钱不够，取不了*/
}
}
===============
package com.wuming.syn.synch;
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){//线程安全
list.add(Thread.currentThread().getName());
}
}).start();
}
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(list.size());//每次运行都不够10000，线程不安全，两个线程同时操作同一个位置，
//两个数组添加到同一个位置，就会覆盖掉，元素就会少
}
}
10000
