synchronized 用法有两种，简单区分：
-
synchronized函数 -- 程序只有一个类，把实际操作的函数从run()方法 独立出来，在该函数定义前面加一个synchronized关键字（private synchronized void buy()） -
synchronized代码块 -- 程序有两个类以上，把实际要操作的变量所在对象找到
synchronized (account){
// 判断有没有钱
if (drawingMoney > account.money) {
System.out.println(Thread.currentThread().getName()+"钱不够了，取不了");
return;
}
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
// 卡内余额
account.money = account.money - drawingMoney;
nowMoney = nowMoney + drawingMoney;
System.out.println(account.name+"余额为："+account.money);
// System.out.println(Thread.currentThread().getName());
System.out.println(this.getName()+"手里的钱"+nowMoney);
}
三个例子
1.抢票程序（线程不安全版）
package demo04_synchronized;
// 不安全地买票
// 线程不安全，有负数
// WARNING！！
// 每个线程在自己的工作内存交互，内存控制不当会造成数据不一致
public class UnsafeBuyTicket {
public static void main(String[] args) {
BuyTicket station = new BuyTicket();
new Thread(station, "苦逼的我们").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; // 外部停止方式
@Override
public void run() {
// 买票
while (flag){
buy();
}
}
private void buy(){
// 判断是否有票
if (ticketNums <= 0) {
flag = false;
return;
}
// 延时设置
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
// 买票
System.out.println(Thread.currentThread().getName()+
"买到第"+ticketNums--+"张票");
}
}
抢票程序改进版
只是在 buy() 函数前加了个 synchronized
package demo04_synchronized;
// 不安全地买票
// 线程不安全，有负数
// WARNING！！
// 每个线程在自己的工作内存交互，内存控制不当会造成数据不一致
public class UnsafeBuyTicket {
public static void main(String[] args) {
BuyTicket station = new BuyTicket();
new Thread(station, "苦逼的我们").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; // 外部停止方式
@Override
public void run() {
// 买票
while (flag){
buy();
}
}
private synchronized void buy(){
// 判断是否有票
if (ticketNums <= 0) {
flag = false;
return;
}
// 延时设置
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
// 买票
System.out.println(Thread.currentThread().getName()+
"买到第"+ticketNums--+"张票");
}
}
2.银行取钱例子（线程不安全版）
package demo04_synchronized;
// 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) {
Account account = new Account(100, "结婚基金");
Drawing you = new Drawing(account, 50, "you");
Drawing gf = new Drawing(account, 100, "gf");
you.start();
gf.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;
// 手里余额
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() {
// 判断有没有钱
if (drawingMoney > account.money) {
System.out.println(Thread.currentThread().getName()+"钱不够了，取不了");
return;
}
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
// 卡内余额
account.money = account.money - drawingMoney;
nowMoney = nowMoney + drawingMoney;
System.out.println(account.name+"余额为："+account.money);
// System.out.println(Thread.currentThread().getName());
System.out.println(this.getName()+"手里的钱"+nowMoney);
}
}
改进版（线程安全版）
package demo04_synchronized;
// 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) {
Account account = new Account(100, "结婚基金");
Drawing you = new Drawing(account, 50, "you");
Drawing gf = new Drawing(account, 100, "gf");
you.start();
gf.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;
// 手里余额
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() {
// 要判断锁住要操作的对象是谁？就是要增删改查的变量在哪，这里是account，而不是this
synchronized (account){
// 判断有没有钱
if (drawingMoney > account.money) {
System.out.println(Thread.currentThread().getName()+"钱不够了，取不了");
return;
}
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
// 卡内余额
account.money = account.money - drawingMoney;
nowMoney = nowMoney + drawingMoney;
System.out.println(account.name+"余额为："+account.money);
// System.out.println(Thread.currentThread().getName());
System.out.println(this.getName()+"手里的钱"+nowMoney);
}
}
}
3.线程入队列例子（线程不安全版）
package demo04_synchronized;
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(()->{
list.add(Thread.currentThread().getName());
}).start();
}
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(list.size());
}
}
改进版（线程安全版）
package demo04_synchronized;
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++) {
synchronized (list) {
new Thread(()->{
list.add(Thread.currentThread().getName());
}).start();
}
}
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(list.size());
}
}
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