Java的多线程问题，详细讲解多线程安全三种方法

java多线程：

创建多线程有四种方法

程序：一段静态的代码

进程：正在运行的程序

线程：一个程序内部的一条执行路径

 

 

 

 

 

为什么不用 .run();

 

 

常用方法：

 

 

 

 

 

优先级不是绝对的。

三个窗口卖票

方法一：

public class windowstest {

public static void main(String[] args) {

window t1=new window();

window t2=new window();

window t3=new window();

t1.setName("窗口1");

t2.setName("窗口2");

t3.setName("窗口3");

t1.start();

t2.start();

t3.start();

}

}

 

class window extends Thread{

private static int ticket=100;//用static静态才能正常

@Override

public void run() {

while(true){

if(ticket>0){

System.out.println(getName()+": 买票，票号为："+ticket);

ticket--;

}else{

break;

}

}

}

}

 

方法二：

 

public class windowtest2 {

public static void main(String[] args) {

mthread m = new mthread();

 

Thread t2 = new Thread(m);

Thread t3 = new Thread(m);

Thread t4 = new Thread(m);

 

t2.setName("窗口一：");

t3.setName("窗口二：");

t4.setName("窗口三：");

 

t2.start();

t3.start();

t4.start();

}

}

class mthread implements Runnable{

private int ticket=100;//用Runnable不用加static

@Override

public void run() {

while(true){

 

if(ticket>0){

System.out.println(Thread.currentThread().getName()+": 买票，票号为："+ticket);

ticket--;

}else{

break;

}

}

}

}

 

 

 

解决线程安全问题：

 

 

 

 

方法一：同步代码块

synchronized（同步监视器）{ }

不能包多，也不能包少了

接口实现多线程

class mthread implements Runnable{

private int ticket=100;//用Runnable不用加static

public void run() {

while(true) {

synchronized (this) {

if (ticket > 0) {

try {

Thread.sleep(100);

} catch (InterruptedException e) {

e.printStackTrace();

}

System.out.println(Thread.currentThread().getName() + ": 买票，票号为：" + ticket);

ticket--;

} else {

break;

}

}

}

}

}

Runnable接口用this很方便

 

IDEA格式化快捷键：

ctrl+alt+L

 

子类继承多线程

public class windowstest {

 

public static void main(String[] args) {

window t1 = new window();

window t2 = new window();

window t3 = new window();

 

t1.setName("窗口1");

t2.setName("窗口2");

t3.setName("窗口3");

 

t1.start();

t2.start();

t3.start();

}

}

class window extends Thread {

private static int ticket = 100;//用static静态才能正常

 

public void run() {

while (true) {

synchronized (window.class) {

 

if (ticket > 0) {

try {

Thread.sleep(100);

} catch (InterruptedException e) {

e.printStackTrace();

}

System.out.println(getName() + ": 买票，票号为：" + ticket);

ticket--;

} else {

break;

}

}

}

}}

window.class只会加载一次

方法二：

public synchronized void show() { }（同步方法）

Runnable接口多线程

public class windowtest2 {

public static void main(String[] args) {

mthread m = new mthread();

 

Thread t2 = new Thread(m);

Thread t3 = new Thread(m);

Thread t4 = new Thread(m);

 

t2.setName("窗口一：");

t3.setName("窗口二：");

t4.setName("窗口三：");

t2.start();

t3.start();

t4.start();

}

 

}

 

class mthread implements Runnable {

private int ticket = 100;//用Runnable不用加static

public void run() {

while (true) {

show();

}

}

public synchronized void show() { //同步监视器是this

if (ticket > 0) {

try {

Thread.sleep(100);

} catch (InterruptedException e) {

e.printStackTrace();

}

System.out.println(Thread.currentThread().getName() + ": 买票，票号为：" + ticket);

ticket--;

}

}

}

 

 

子类继承多线程

 

public class windowstest {

 

public static void main(String[] args) {

window t1 = new window();

window t2 = new window();

window t3 = new window();

 

t1.setName("窗口1");

t2.setName("窗口2");

t3.setName("窗口3");

 

t1.start();

t2.start();

t3.start();

}

}

class window extends Thread {

 

 

private static int ticket = 100;//用static静态才能正常

public void run() {

while (true) {

show();

}

}

public static synchronized void show(){ //同步监视器：window.class

//public synchronized void show() { 同步监视器：t1,t2,t3必须加static才行

if (ticket > 0) {

try {

Thread.sleep(100);

} catch (InterruptedException e) {

e.printStackTrace();

}

System.out.println(Thread.currentThread().getName() + ": 买票，票号为：" + ticket);

ticket--;

}

}

 

}

 

synchronized前面要加static

 

 

死锁

包围快捷键：

 

 

方法三：lock