Java 指定线程执行顺序（三种方式）

方法一：通过共享对象锁加上可见变量来实现

/**
* 指定线程执行顺序：通过synchronized共享对象锁加上volatile可见变量来实现
*/
public class ThreadOrder {

private volatile int orderNum = 1;

public synchronized void methodA() {
try {
while (orderNum != 1) {
wait();
}
for (int i = 0; i < 2; i++) {
System.out.println("AAAAA");
}
orderNum = 2;
notifyAll();
} catch (InterruptedException e) {
e.printStackTrace();
}
}

public synchronized void methodB() {
try {
while (orderNum != 2) {
wait();
}
for (int i = 0; i < 2; i++) {
System.out.println("BBBBB");
}
orderNum = 3;
notifyAll();
} catch (InterruptedException e) {
e.printStackTrace();
}
}

public synchronized void methodC() {
try {
while (orderNum != 3) {
wait();
}
for (int i = 0; i < 2; i++) {
System.out.println("CCCCC");
}
orderNum = 1;
notifyAll();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}

测试类：

package com.example.concurrent;

import org.junit.Test;

public class ThreadOrderTest {

/**
* 指定线程执行顺序：通过共享对象锁加上可见变量来实现
*
* @throws Exception
*/
@Test
public void test() throws Exception {
ThreadOrder threadOrder = new ThreadOrder();

Thread thread1 = new Thread(new Runnable() {

@Override
public void run() {
// TODO Auto-generated method stub
threadOrder.methodA();
}
});

Thread thread2 = new Thread(new Runnable() {

@Override
public void run() {
// TODO Auto-generated method stub
threadOrder.methodB();
}
});

Thread thread3 = new Thread(new Runnable() {

@Override
public void run() {
// TODO Auto-generated method stub
threadOrder.methodC();
}
});

thread1.start();
thread2.start();
thread3.start();
}
}

执行结果：

AAA
AAA
BBB
BBB
CCC
CCC

可以看到线程的启动按顺序执行了。共享对象锁，可以保证每个方法只能同时有一个线程进入，配合wait和notifyAll方法，可以启动或者唤醒线程。

方法二：通过主线程Join()

join()方法的意思是等待线程执行完程序后死亡。

测试类：

package com.example.concurrent;

import org.junit.Test;

public class ThreadOrderTest {

/**
* 通过主线程join()
*
* @throws Exception
*/
@Test
public void test2() throws Exception {
Thread thread1 = new Thread(new Runnable() {

@Override
public void run() {
// TODO Auto-generated method stub
System.out.println("AAA");
}
});

Thread thread2 = new Thread(new Runnable() {

@Override
public void run() {
// TODO Auto-generated method stub
System.out.println("BBB");
}
});

Thread thread3 = new Thread(new Runnable() {

@Override
public void run() {
// TODO Auto-generated method stub
System.out.println("CCC");
}
});

thread1.start();
thread1.join();
thread2.start();
thread2.join();
thread3.start();
thread3.join();
}
}

执行结果：

AAA
BBB
CCC

方法三：通过线程执行时Join()

class T1 extends Thread {
public void run(){
Random random = new Random();
try {
Thread.sleep(random.nextInt(1000));
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("in T1");
}
}

class T2 extends Thread{
private Thread thread;
public T2(Thread thread) {
this.thread = thread;
}

public void run(){
try {
thread.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("in T2");
}
}

class T3 extends Thread{
private Thread thread;
public T3(Thread thread) {
this.thread = thread;
}

public void run(){
try {
thread.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("in T3");
}
}

public class Test {
public static void main(String[] args) throws InterruptedException {
T1 t1 = new T1();
T2 t2 = new T2(t1);
T3 t3 = new T3(t2);
t2.start();
t1.start();
t3.start();
}
}

执行结果：

in T1
in T2
in T3