java守護線程，顧名思義，守護的是主進程，當主線程結束了，守護線程也就結束了

我們看代碼

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public class ThreadDemo {public static void main(String[] args) {Message message = new Message();Runnable adder = new Adder(message);Runnable suber = new Suber(message);Thread thread1 = new Thread(adder, "adder");Thread thread2 = new Thread(suber, "suber");thread1.start();thread2.start();} }class Adder implements Runnable {private Message msg;public Adder(Message message){this.msg=message;}@Overridepublic void run() {for(int i = 0 ; i < 50;i++){try {Thread.sleep(150);} catch (InterruptedException e) {e.printStackTrace();}msg.add();}} }class Suber implements Runnable {private Message msg;public Suber(Message message){this.msg=message;}@Overridepublic void run() {for(int i = 0 ; i < 25 ;i++){try {Thread.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}msg.sub();}} }class Message{private int num;public Message() {this.num =0;}public synchronized void add() {num++;System.out.println(Thread.currentThread().getName()+",num:"+num);}public synchronized void sub(){num--;System.out.println(Thread.currentThread().getName()+",num:"+num);} }

執行結果，adder和suber交替執行。然后因為adder操作更多一些，后面就更多執行了

我們稍作改動

添加一行

thread1.setDaemon(true);

完整代碼

public class ThreadDemo {public static void main(String[] args) {Message message = new Message();Runnable adder = new Adder(message);Runnable suber = new Suber(message);Thread thread1 = new Thread(adder, "adder");Thread thread2 = new Thread(suber, "suber");thread1.setDaemon(true);thread1.start();thread2.start();} }class Adder implements Runnable {private Message msg;public Adder(Message message){this.msg=message;}@Overridepublic void run() {for(int i = 0 ; i < 50;i++){try {Thread.sleep(150);} catch (InterruptedException e) {e.printStackTrace();}msg.add();}} }class Suber implements Runnable {private Message msg;public Suber(Message message){this.msg=message;}@Overridepublic void run() {for(int i = 0 ; i < 25 ;i++){try {Thread.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}msg.sub();}} }class Message{private int num;public Message() {this.num =0;}public synchronized void add() {num++;System.out.println(Thread.currentThread().getName()+",num:"+num);}public synchronized void sub(){num--;System.out.println(Thread.currentThread().getName()+",num:"+num);} }

?

由執行結果可以看出，把adder設置成為守護線程，suber結束后，adder就也結束了。

此外，java中最大的守護線程是GC，當所有線程結束了，GC也就結束了。

總結

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