java中设置线程的优先级使用 setPriority()方法,JDK源码如下:
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);
}
}
线程的优先级有1~10 10个等级，在范围之外则抛出异常:throw new IllegalArgumentException()
JDK中预定义了三个优先级常量的值:
/**
* The minimum priority that a thread can have.
*/
public final static int MIN_PRIORITY = 1;
/**
* The default priority that is assigned to a thread.
*/
public final static int NORM_PRIORITY = 5;
/**
* The maximum priority that a thread can have.
*/
public final static int MAX_PRIORITY = 10;
线程的优先级具有继承性
所谓继承性，就是例如：A线程启动B线程，则B线程具有与A线程相同的优先级。
通过打印this.getPriority()的值可以查看。
线程的优先级具有规则性
优先级越高的越容易被CUP先执行完，和代码的顺序无关
线程的优先级具有随机性
前边说过优先级越高越容易先执行完，而不是完全，只是大概率，因为线程的执行是随机的，设置高的优先级，只是提高先被执行的概率。
不要把优先级与运行结果的顺序作为衡量的标志，优先级高的线程并不一定先执行完run()，线程的优先级与打印顺序无关,它们的关系具有不确定性和随机性
示例:
ThreadPriorityA.java
package com.zhxin.threadLab;
/**
* @ClassName ThreadPriorityA
* @Description //countPriority
* @Author singleZhang
* @Email 405780096@qq.com
* @Date 2020/11/26 0026 下午 4:24
**/
public class ThreadPriorityA extends Thread {
private int count = 0;
public int getCount(){
return count;
}
@Override
public void run(){
while (true){
count ++;
}
}
}
ThreadPriorityB.java
package com.zhxin.threadLab;
/**
* @ClassName ThreadPriorityB
* @Description //countPriority
* @Author singleZhang
* @Email 405780096@qq.com
* @Date 2020/11/26 0026 下午 4:26
**/
public class ThreadPriorityB extends Thread {
private int count = 0;
public int getCount(){
return count;
}
@Override
public void run(){
while (true){
count ++;
}
}
}
CountPriorityTest.java
package com.zhxin.threadLab.test;
import com.zhxin.threadLab.ThreadPriorityA;
import com.zhxin.threadLab.ThreadPriorityB;
/**
* @ClassName CountPriorityTest
* @Description //CountPriorityTest
* @Author singleZhang
* @Email 405780096@qq.com
* @Date 2020/11/26 0026 下午 4:26
**/
public class CountPriorityTest {
public static void main(String[] args){
try {
ThreadPriorityA a = new ThreadPriorityA();
a.setPriority(Thread.MIN_PRIORITY);
a.start();
ThreadPriorityB b = new ThreadPriorityB();
b.setPriority(Thread.MAX_PRIORITY);
b.start();
Thread.sleep(1000);
a.stop();// 不建议用stop,不过测试没关系
b.stop();
System.out.println("aCount="+a.getCount());
System.out.println("bCount="+b.getCount());
}catch (InterruptedException e){
e.printStackTrace();
}
}
}
运行结果如下:
countPriority
