Java 線程的優(yōu)先級(setPriority)案例詳解

更新時(shí)間：2021年08月27日 12:02:21 作者：飛少fly

這篇文章主要介紹了Java 線程的優(yōu)先級(setPriority)案例詳解,本篇文章通過簡要的案例,講解了該項(xiàng)技術(shù)的了解與使用,以下就是詳細(xì)內(nèi)容,需要的朋友可以參考下

線程可以劃分優(yōu)先級，優(yōu)先級高的線程得到的CPU資源比較多，也就是CPU優(yōu)先執(zhí)行優(yōu)先級高的線程對象中的任務(wù)。

設(shè)置線程優(yōu)先級有助于幫助線程規(guī)劃器確定下一次選中哪一個(gè)線程優(yōu)先執(zhí)行。

java中優(yōu)先級分為1-10個(gè)級別

線程優(yōu)先級的繼承特性例如a線程啟迪b線程，則b線程的優(yōu)先級與a的一樣。

代碼說話：（很簡單）

public class MyThread1 extends Thread {
	@Override
	public void run() {
		System.out.println("MyThread1 run priority=" + this.getPriority());
		MyThread2 thread2 = new MyThread2();
		thread2.start();
	}
}
 
 
public class MyThread2 extends Thread {
	@Override
	public void run() {
		System.out.println("MyThread2 run priority=" + this.getPriority());
	}
}
 
public static void main(String[] args) {
		System.out.println("main thread begin priority="
				+ Thread.currentThread().getPriority());
		
		Thread.currentThread().setPriority(6);
		
		System.out.println("main thread end   priority="
				+ Thread.currentThread().getPriority());
		
		MyThread1 thread1 = new MyThread1();
		thread1.start();
	}

優(yōu)先級具有規(guī)則性

public class MyThread1 extends Thread {
	@Override
	public void run() {
		long beginTime = System.currentTimeMillis();
		long addResult = 0;
		for (int j = 0; j < 10; j++) {
			for (int i = 0; i < 50000; i++) {
				Random random = new Random();
				random.nextInt();
				addResult = addResult + i;
			}
		}
		long endTime = System.currentTimeMillis();
		System.out.println("★★★★★thread 1 use time=" + (endTime - beginTime));
	}
}
 
public class MyThread2 extends Thread {
	@Override
	public void run() {
		long beginTime = System.currentTimeMillis();
		long addResult = 0;
		for (int j = 0; j < 10; j++) {
			for (int i = 0; i < 50000; i++) {
				Random random = new Random();
				random.nextInt();
				addResult = addResult + i;
			}
		}
		long endTime = System.currentTimeMillis();
		System.out.println("☆☆☆☆☆thread 2 use time=" + (endTime - beginTime));
	}
}
 
public static void main(String[] args) {
		for (int i = 0; i < 5; i++) {
			MyThread1 thread1 = new MyThread1();
			thread1.setPriority(1);
			thread1.start();
 
			MyThread2 thread2 = new MyThread2();
			thread2.setPriority(10);
			thread2.start();
		}
	}

高優(yōu)先級的線程總是先執(zhí)行完

線程的優(yōu)先級和代碼的執(zhí)行順序沒有關(guān)系

優(yōu)先級具有隨機(jī)性

一般優(yōu)先級較高的線程先執(zhí)行run()方法，但是這個(gè)不能說的但肯定，因?yàn)榫€程的優(yōu)先級具有 “隨機(jī)性”也就是較高線程不一定每一次都先執(zhí)行完。

public class MyThread1 extends Thread {
	@Override
	public void run() {
		long beginTime = System.currentTimeMillis();
		for (int i = 0; i < 1000; i++) {
			Random random = new Random();
			random.nextInt();
		}
		long endTime = System.currentTimeMillis();
		System.out.println("★★★★★thread 1 use time=" + (endTime - beginTime));
	}
}
 
public class MyThread2 extends Thread {
	@Override
	public void run() {
		long beginTime = System.currentTimeMillis();
		for (int i = 0; i < 1000; i++) {
			Random random = new Random();
			random.nextInt();
		}
		long endTime = System.currentTimeMillis();
		System.out.println("☆☆☆☆☆thread 2 use time=" + (endTime - beginTime));
	}
}
 
 
public static void main(String[] args) {
		for (int i = 0; i < 5; i++) {
			MyThread1 thread1 = new MyThread1();
			thread1.setPriority(5);
			thread1.start();
 
			MyThread2 thread2 = new MyThread2();
			thread2.setPriority(6);
			thread2.start();
		}
	}

守護(hù)線程介紹：

java 中有兩種線程一個(gè)是用戶線程，一個(gè)是守護(hù)（Daemon）線程

典型的守護(hù)線程就是垃圾回收線程，如果進(jìn)程中沒有非守護(hù)線程了，則守護(hù)線程自動(dòng)銷毀。

守護(hù)線程作用就是為其他線程的運(yùn)行提供便利的服務(wù)，比如GC。

public class MyThread extends Thread {
	private int i = 0;
 
	@Override
	public void run() {
		try {
			while (true) {
				i++;
				System.out.println("i=" + (i));
				Thread.sleep(1000);
			}
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}
 
 
public static void main(String[] args) {
		try {
			MyThread thread = new MyThread();
			thread.setDaemon(true);//設(shè)置守護(hù)線程
			thread.start();
			Thread.sleep(5000);
			System.out.println("我離開thread對象也不再打印了，也就是停止了！");
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

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