Java多线程基础学习（一）

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1. 创建线程

1.1 通过构造函数：public Thread(Runnable target, String name){} 或：public Thread(Runnable target){}

示例:

Thread thread1 = new Thread(new MyThread(), "mythread");
class MyThread extends Thread(){
public void run(){
System.out.println("My First Thread');
}
}

1.2 直接实现Runnable接口：

示例：

Thread thread2 = new Thread(new Runnable{}{
public void run(){
System.out.println("This is my thread.");
}
});

2. 运行线程

thead1.start()

3. sleep

try{
#休眠1000ms
Thread.sleep(1000);
}catch(InterruptedException e){
e.printStackTrace();
}

4. getName() 获取线程名字， getId()获取线程id

System.out.println(Thread.currentThread().getName() + ":"+ Thread.currentThread().getId);

5. 停止线程，

千万不用stop()，stop会立即终止线程。

通过interrupt()中断线程，但是中断并没有停止线程，配合异常来实现：

public class Main {
public static void main(String[] args) throws InterruptedException {
try{
Thread thread1=new Thread(new TheThread(),"thread1");
thread1.start();
Thread.sleep(2000);
thread1.interrupt();
}catch (InterruptedException e){
e.printStackTrace();
}
}
}
class TheThread extends Thread{
public void run() {
super.run();
for (int i = 0; i < 10; i++) {
if(this.interrupted()){
break;
}
System.out.println(Thread.currentThread().getName() + ":" + i);
}
}
}

注意，如果在TheThread类里加入catch InterruptException的话，可能会导致interrupt被捕获，而绕过if（this.interrupted()）的判断而无法终止线程。

6. 等待和通知

线程等待：当前线程就处于等待状态，直到其他线程调用了notify()方法，线程才会继续执行

public final void wait() throws InterruptedException

线程通知：

public final native void notify()

注意：在notify()方法后，当前线程不会马上释放该对象锁，要等到执行notify()方法的线程将程序执行完，也就是退出同步代码块中。

package wait.notify; public class ThreadWaitNotifyTest {
final static Object object=new Object();
public static class T1 extends Thread{
public void run(){
System.out.println(System.currentTimeMillis()+": T1 start");
synchronized (object){
try {
System.out.println(System.currentTimeMillis()+": T1 wait");
object.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println(System.currentTimeMillis()+": T1 end");
}
}
public static class T2 extends Thread{
public void run(){
System.out.println(System.currentTimeMillis()+": T2 start");
synchronized (object){
System.out.println("T2 synchonized code start.");
object.notify();
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}finally{
System.out.println("T2 synchonized code end.");
} }
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(System.currentTimeMillis()+": T2 end");
}
}
public static void main(String[] args){
Thread thread1=new T1();
Thread thread2=new T2();
thread1.start();
thread2.start();
}
}

输出结果：

7. 线程优先级

高优先级的线程将会获得更多的CPU资源。一共分为10个优先级。

public final void setPriority(int newPriority)

源码分析：

public final void setPriority(int newPriority) {
ThreadGroup g;
checkAccess();
if (newPriority > MAX_PRIORITY || newPriority < MIN_PRIORITY) {
throw new IllegalArgumentException();
}
if((g = getThreadGroup()) != null) {
if (newPriority > g.getMaxPriority()) {
newPriority = g.getMaxPriority();
}
setPriority0(priority = newPriority);
}
}

public final static int MIN_PRIORITY = 1;
public final static int NORM_PRIORITY = 5;
public final static int MAX_PRIORITY = 10;

可见线程最高优先级为10, 最低为1，默认为5.

当设定的newPriority高于该线程组ThreadGroup的最高Priority时，只能分配该线程组的最高Priority

8. 守护线程

类似守护进程，Java存在两种线程：用户线程和守护线程。它是一种特殊线程，执行的是一种后台服务，当一个系统中不存在非守护线程的时候，守护线程会自己销毁。典型的守护线程：JVM的垃圾回收线程。

public final void setDaemon(boolean on)

示例：

public class Main {
public static void main(String[] args) throws InterruptedException {
TheThread theThread=new TheThread();
theThread.setDaemon(true);//设置守护线程
theThread.start();
Thread.sleep(5000);
System.out.println("全都退出啦");
}
public static class TheThread extends Thread{
public void run(){
int i = 0;
while (true){
i++;
System.out.println(Thread.currentThread().getId()+":"+i);
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
}