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Java讓多線程按順序執(zhí)行的幾種方法

更新時(shí)間：2022年05月03日 11:57:22 作者：Jqcode

本文主要介紹了Java讓多線程按順序執(zhí)行的幾種方法，文中通過示例代碼介紹的非常詳細(xì)，對(duì)大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價(jià)值，需要的朋友們下面隨著小編來一起學(xué)習(xí)學(xué)習(xí)吧

在子線程中通過join()方法指定順序

通過join()方法使當(dāng)前線程“阻塞”，等待指定線程執(zhí)行完畢后繼續(xù)執(zhí)行。舉例：在線程thread2中，加上一句thread1.join()，其意義在于，當(dāng)前線程2運(yùn)行到此行代碼時(shí)會(huì)進(jìn)入阻塞狀態(tài)，直到線程thread1執(zhí)行完畢后，線程thread2才會(huì)繼續(xù)運(yùn)行，這就保證了線程thread1與線程thread2的運(yùn)行順序。

public class ThreadJoinDemo {
    public static void main(String[] args) throws InterruptedException {
        final Thread thread1 = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("打開冰箱！");
            }
        });
 
        final Thread thread2 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    thread1.join();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("拿出一瓶牛奶！");
            }
        });
 
        final Thread thread3 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    thread2.join();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("關(guān)上冰箱！");
            }
        });
 
        //下面三行代碼順序可隨意調(diào)整，程序運(yùn)行結(jié)果不受影響，因?yàn)槲覀冊谧泳€程中通過“join()方法”已經(jīng)指定了運(yùn)行順序。
        thread3.start();
        thread2.start();
        thread1.start();
 
    }
}

運(yùn)行結(jié)果：

打開冰箱！
拿出一瓶牛奶！
關(guān)上冰箱！

在主線程中通過join()方法指定順序

簡單說一下子線程與主線程的區(qū)別，子線程指的是發(fā)生在Thread內(nèi)部的代碼，主線程指的是發(fā)生在main函數(shù)中的代碼，我們可以在main函數(shù)中通過join()方法讓主線程阻塞等待以達(dá)到指定順序執(zhí)行的目的。

public class ThreadMainJoinDemo {
    public static void main(String[] args) throws InterruptedException {
        final Thread thread1 = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("打開冰箱！");
            }
        });
 
        final Thread thread2 = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("拿出一瓶牛奶！");
            }
        });
 
        final Thread thread3 = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("關(guān)上冰箱！");
            }
        });
 
        thread1.start();
        thread1.join();
        thread2.start();
        thread2.join();
        thread3.start();
    }
}

輸出結(jié)果：

打開冰箱！
拿出一瓶牛奶！
關(guān)上冰箱！

通過倒數(shù)計(jì)時(shí)器CountDownLatch實(shí)現(xiàn)

CountDownLatch通過計(jì)數(shù)器提供了更靈活的控制，只要檢測到計(jì)數(shù)器為0當(dāng)前線程就可以往下執(zhí)行而不用管相應(yīng)的thread是否執(zhí)行完畢。

public class ThreadCountDownLatchDemo {
 
    private static CountDownLatch countDownLatch1 = new CountDownLatch(1);
 
    private static CountDownLatch countDownLatch2 = new CountDownLatch(1);
 
    public static void main(String[] args) {
        final Thread thread1 = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("打開冰箱！");
                countDownLatch1.countDown();
            }
        });
 
        final Thread thread2 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    countDownLatch1.await();
                    System.out.println("拿出一瓶牛奶！");
                    countDownLatch2.countDown();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
 
        final Thread thread3 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    countDownLatch2.await();
                    System.out.println("關(guān)上冰箱！");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
 
        //下面三行代碼順序可隨意調(diào)整，程序運(yùn)行結(jié)果不受影響
        thread3.start();
        thread1.start();
        thread2.start();
    }
}

輸出結(jié)果：

打開冰箱！
拿出一瓶牛奶！
關(guān)上冰箱！

通過創(chuàng)建單一化線程池newSingleThreadExecutor()實(shí)現(xiàn)

單線程化線程池(newSingleThreadExecutor)的優(yōu)點(diǎn)，串行執(zhí)行所有任務(wù)。

public class ThreadPoolDemo {
 
   static ExecutorService executorService = Executors.newSingleThreadExecutor();
 
    public static void main(String[] args) {
        final Thread thread1 = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("打開冰箱！");
            }
        });
 
        final Thread thread2 =new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("拿出一瓶牛奶！");
            }
        });
 
        final Thread thread3 = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("關(guān)上冰箱！");
            }
        });
        executorService.submit(thread1);
        executorService.submit(thread2);
        executorService.submit(thread3);
        executorService.shutdown();        //使用完畢記得關(guān)閉線程池
    }
 
}

輸出結(jié)果：