Java多線程基礎(chǔ)
一、線程
什么是線程:
線程是進(jìn)程的一個(gè)實(shí)體,是CPU調(diào)度和分派的基本單位,它是比進(jìn)程更小的能獨(dú)立運(yùn)行的基本單位。
什么是多線程:
多線程指在單個(gè)程序中可以同時(shí)運(yùn)行多個(gè)不同的線程執(zhí)行不同的任務(wù)。
二、創(chuàng)建多線程的方式
多線程的創(chuàng)建方式有三種:Thread
、Runnable
、Callable
1、繼承Thread類實(shí)現(xiàn)多線程
Thread thread = new Thread() { @Override public void run() { super.run(); while (true) { try { Thread.sleep(500); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("1:" + Thread.currentThread().getName()); System.out.println("2:" + this.getName()); } } }; thread.start();
2、實(shí)現(xiàn)Runnable接口方式實(shí)現(xiàn)多線程
Thread thread1 = new Thread(new Runnable() { @Override public void run() { while (true) { try { Thread.sleep(500); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("3:" + Thread.currentThread().getName()); } } }); thread1.start();
3、Callable接口創(chuàng)建線程
public class CallableTest { public static void main(String[] args) { System.out.println("當(dāng)前線程是:" + Thread.currentThread()); Callable myCallable = new Callable() { @Override public Integer call() throws Exception { int i = 0; for (; i < 10; i++) { } //當(dāng)前線程 System.out.println("當(dāng)前線程是:" + Thread.currentThread() + ":" + i); return i; } }; FutureTask<Integer> fu = new FutureTask<Integer>(myCallable); Thread th = new Thread(fu, "callable thread"); th.start(); //得到返回值 try { System.out.println("返回值是:" + fu.get()); } catch (Exception e) { e.printStackTrace(); } } }
當(dāng)前線程是:Thread[main,5,main]
當(dāng)前線程是:Thread[callable thread,5,main]:10
返回值是:10
總結(jié):
實(shí)現(xiàn)Runnable
接口相比繼承Thread類有如下優(yōu)勢(shì):
- 可以避免由于Java的單繼承特性而帶來的局限;
- 增強(qiáng)程序的健壯性,代碼能夠被多個(gè)線程共享,代碼與數(shù)據(jù)是獨(dú)立的;
- 適合多個(gè)相同程序代碼的線程區(qū)處理同一資源的情況。
實(shí)現(xiàn)Runnable
接口和實(shí)現(xiàn)Callable
接口的區(qū)別:
Runnable
是自從java1.1
就有了,而Callable
是1.5之后才加上去的Callable
規(guī)定的方法是call()
,Runnable
規(guī)定的方法是run()
Callable
的任務(wù)執(zhí)行后可返回值,而Runnable
的任務(wù)是不能返回值是(void)- call方法可以拋出異常,run方法不可以
- 運(yùn)行Callable任務(wù)可以拿到一個(gè)Future對(duì)象,表示異步計(jì)算的結(jié)果。它提供了檢查計(jì)算是否完成的方法,以等待計(jì)算的完成,并檢索計(jì)算的結(jié)果。通過Future對(duì)象可以了解任務(wù)執(zhí)行情況,可取消任務(wù)的執(zhí)行,還可獲取執(zhí)行結(jié)果。
- 加入線程池運(yùn)行,
Runnable
使用ExecutorService
的execute
方法,Callable
使用submit
方法。
三、線程的生命周期與狀態(tài)

四、線程的執(zhí)行順序
Join
線程的運(yùn)行順序
原理:
1、定時(shí)器
import java.util.Timer; import java.util.TimerTask; public class TraditionalTimerTest { public static void main(String[] args) { // new Timer().schedule(new TimerTask() { // @Override // public void run() { // // System.out.println("bombing!"); // } // },10000); class MyTimberTask extends TimerTask { @Override public void run() { System.out.println("bombing!"); new Timer().schedule(new MyTimberTask(), 2000); } } new Timer().schedule(new MyTimberTask(), 2000); int count = 0; while (true) { System.out.println(count++); try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } } } }
0
1
bombing!
2
3
bombing!
4
5
bombing!
6
省略...
2、線程的互斥與同步通信
public class TraditionalThreadSynchronized { public static void main(String[] args) { new TraditionalThreadSynchronized().init(); } private void init() { final Outputer outputer = new Outputer(); new Thread(new Runnable() { @Override public void run() { while (true) { try { Thread.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); } outputer.output("kpioneer"); } } }).start(); // new Thread(new Runnable() { // @Override // public void run() { // // while (true) { // try { // Thread.sleep(10); // } catch (InterruptedException e) { // e.printStackTrace(); // } // outputer.output2("Tom"); // // } // } // }).start(); new Thread(new Runnable() { @Override public void run() { while (true) { try { Thread.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); } outputer.output3("Jack"); } } }).start(); } static class Outputer { public void output(String name) { int len = name.length(); synchronized (Outputer.class) { for (int i = 0; i < len; i++) { System.out.print(name.charAt(i)); } System.out.println(); } } public synchronized void output2(String name) { int len = name.length(); for (int i = 0; i < len; i++) { System.out.print(name.charAt(i)); } System.out.println(); } public static synchronized void output3(String name) { int len = name.length(); for (int i = 0; i < len; i++) { System.out.print(name.charAt(i)); } System.out.println(); } } }
3、線程同步通信技術(shù)
子線程循環(huán)10次,接著主線程循環(huán)100,接著又回到子線程循環(huán)10次,接著再回到主線程有循環(huán)100,如此循環(huán)50次,請(qǐng)寫出程序。
public class TraditionalThreadCommunication { public static void main(String[] args) { final Business business = new Business(); new Thread(new Runnable() { @Override public void run() { for (int i = 1; i <= 50; i++) { business.sub(i); } } } ).start(); for (int i = 1; i <= 50; i++) { business.main(i); } } } /** *要用到共同數(shù)據(jù)(包括同步鎖)的若干方法應(yīng)該歸在同一個(gè)類身上, * 這種設(shè)計(jì)正好體現(xiàn)了高類聚和和程序的健壯性 */ class Business { private boolean bShouldSub = true; public synchronized void sub(int i) { if(!bShouldSub) { try { this.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } for (int j = 1; j <= 10; j++) { System.out.println("sub thread sequece of " + j + ",loop of " + i); } bShouldSub = false; this.notify(); } public synchronized void main(int i) { if(bShouldSub) { try { this.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } for (int j = 1; j <=100; j++) { System.out.println("main thread sequece of " + j + ",loop of " + i); } bShouldSub = true; this.notify(); } }
sub thread sequece of 1,loop of 1
sub thread sequece of 2,loop of 1
sub thread sequece of 3,loop of 1
sub thread sequece of 4,loop of 1
sub thread sequece of 5,loop of 1
sub thread sequece of 6,loop of 1
sub thread sequece of 7,loop of 1
sub thread sequece of 8,loop of 1
sub thread sequece of 9,loop of 1
sub thread sequece of 10,loop of 1
main thread sequece of 1,loop of 1
main thread sequece of 2,loop of 1
main thread sequece of 3,loop of 1
main thread sequece of 4,loop of 1
main thread sequece of 5,loop of 1
main thread sequece of 6,loop of 1
main thread sequece of 7,loop of 1
main thread sequece of 8,loop of 1
main thread sequece of 9,loop of 1
main thread sequece of 10,loop of 1
main thread sequece of 11,loop of 1
省略中間...
main thread sequece of 99,loop of 1
main thread sequece of 100,loop of 1
sub thread sequece of 1,loop of 2
sub thread sequece of 2,loop of 2
sub thread sequece of 3,loop of 2
sub thread sequece of 4,loop of 2
sub thread sequece of 5,loop of 2
sub thread sequece of 6,loop of 2
sub thread sequece of 7,loop of 2
sub thread sequece of 8,loop of 2
sub thread sequece of 9,loop of 2
sub thread sequece of 10,loop of 2
main thread sequece of 1,loop of 2
main thread sequece of 2,loop of 2
main thread sequece of 3,loop of 2
省略...
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