线程的管理

 我们使用ThreadGroup对线程进行管理，ThreadGroup具有三个参数，ThreadGroup、Runnable、String：

public Thread(ThreadGroup group, Runnable target, String name)

 例子：

package myTest;public class myTest implements Runnable {public static void main(String[] args) {// 线程组ThreadGroup tg = new ThreadGroup("myGroup");Thread t1 = new Thread(tg, new myTest(), "Thread1");Thread t2 = new Thread(tg, new myTest(), "Thread2");t1.start();t2.start();System.out.println(tg.activeCount());tg.list();}@Overridepublic void run() {String group = Thread.currentThread().getThreadGroup().getName()+"-"+Thread.currentThread().getName();while(true) {System.out.println("This is "+group);try {Thread.sleep(10000);} catch (InterruptedException e) {throw new RuntimeException(e);}}}
}
/**
2
java.lang.ThreadGroup[name=myGroup,maxpri=10]Thread[Thread1,5,myGroup]Thread[Thread2,5,myGroup]
This is myGroup-Thread2
This is myGroup-Thread1
*/

线程的后台

 有些主线程在不断的消耗资源进行运算，而后台线程则负责资源垃圾的回收，等主线程结束以后，后台线程便会自然结束。设置后台线程的方法:

package myTest;public class myTest {public static class test1 implements Runnable {@Overridepublic void run() {try {Thread.sleep(5000);} catch (InterruptedException e) {throw new RuntimeException(e);}}}public static class test2 implements Runnable {@Overridepublic void run() {while (true) {System.out.println("I am alive");try {Thread.sleep(1000);} catch (InterruptedException e) {throw new RuntimeException(e);}}}}public static void main(String[] args) {Thread t1 = new Thread(new test1());Thread t2 = new Thread(new test2());t2.setDaemon(true);t1.start();t2.start();}
}

 线程会在运行后，开始寻找主线程，等待主线程，如果发现没有主线程，或主线程已经结束，只有后台线程才存活，便会结束线程。

线程的优先级

 常用控制着线程的优先级的方法为setPriority()：

package myTest;public class myTest {public static class high implements Runnable {static int count = 0;@Overridepublic void run() {while(true) {synchronized (myTest.class) {count ++;if(count>10000) {System.out.println("high is win");break;}}}}}public static class low implements Runnable {static int count = 0;@Overridepublic void run() {while (true) {synchronized (myTest.class) {count ++;if(count>10000) {System.out.println("low is win");break;}}}}}public static void main(String[] args) {Thread t1 = new Thread(new high());Thread t2 = new Thread(new low());t1.setPriority(10);t2.setPriority(1);t1.start();t2.start();}
}