全文概要
本文主要介绍线程的优先级和守护线程。
- 创建的线程默认的优先级是5，当然可以自行设置优先级，优先级为[1,10]区间的整数；
- java中有两种线程，用户线程和守护线程，可以通过isDaemon()来判断，返回true表示守护线程；
- 用户线程一般用来执行用户级任务，而守护线程一般用来执行后台任务，除此之外，守护线程有一个重要的特性：当所有的用户线程全部执行完毕后，无论守护线程的逻辑是否完成，JVM会自动结束守护线程。
守护线程介绍
- 代码案例
package com.tml.javaCore.thread;
public class DaemoDemo {
public static void main(String[] args) {
Thread thread_01 = new Thread(new Runnable() {
public void run() {
System.out.println(Thread.currentThread().getName() +
":priority is:" + Thread.currentThread().getPriority() );
for(int i=0;i<10;i++){
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + ": is loop " + i);
}
}
}, "thread_01");
thread_01.setPriority(1);
thread_01.start();
Thread thread_02 = new Thread(new Runnable() {
public void run() {
System.out.println(Thread.currentThread().getName() +
":priority is:" + Thread.currentThread().getPriority() );
for(int i=0;i<100;i++){
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName() + ": is loop " + i);
}
}
}, "thread_02");
thread_02.setDaemon(true);//设置守护线程一定要在start()方法之前
thread_02.setPriority(10);
thread_02.start();
}
}
- 输出结果
thread_01:priority is:1
thread_02:priority is:10
thread_01: is loop 0
thread_02: is loop 0
thread_01: is loop 1
thread_02: is loop 1
thread_02: is loop 2
thread_01: is loop 2
thread_02: is loop 3
thread_01: is loop 3
thread_02: is loop 4
thread_01: is loop 4
thread_01: is loop 5
thread_02: is loop 5
thread_01: is loop 6
thread_02: is loop 6
thread_01: is loop 7
thread_02: is loop 7
thread_01: is loop 8
thread_02: is loop 8
thread_01: is loop 9
thread_02: is loop 9
- 结果分析
- 主线程中创建了连个线程，线程1的优先级设置为1，线程2的优先级设置为10，当设置线程优先级的值不在[1,10]整数区间内，会抛出java.lang.IllegalArgumentException运行时异常，除此之外，线程2还被设置为守护线程，注意设置守护线程一定要在start()方法之前，否则会抛出java.lang.IllegalThreadStateException运行时异常；
- 由于打印的时候，线程睡眠100毫秒，这就导致线程1和线程2依次执行打印任务；
- 线程1是用户线程，线程2是守护线程，当线程1执行完成后，JVM会自动结束线程2，即便线程2循环没有结束。