Java多线程基础学习(一)

时间:2022-06-01 13:00:01

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:

Java多线程基础学习(一)

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();
}
}
}
}
}
源码分析:
设置线程为用户线程(user thread)或守护线程(daemon thread),当剩余运行的线程均为守护线程时,JVM会退出。
 public final void setDaemon(boolean on) {
checkAccess();
if (isAlive()) {
throw new IllegalThreadStateException();
}
daemon = on;
}
其中checkAccesss()方法如下:
 public final void checkAccess() {
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkAccess(this);
}
}
该方法用于判断当前运行的线程是否有修改此线程的权限。
而public final native boolean isAlive();用于判断该线程是否处于alive状态,即该线程是否已经start,且没有die。
当isAlive的话就会抛出IllegalThreadStateException异常。
所以,设置守护线程的方法,逻辑就是先判断当前线程是否有修改的权限,再判断是否处于alive状态,如果不处于alive状态,则根据boolean变量on的值更改它的状态,即true:设为daemon线程,false:设为user线程。