??類ThreadLocal主要解決的就是每個線程綁定自己的值,可以將ThreadLocal類比喻成全局存放數據的盒子,盒子中可以存儲每個線程的私有數據。

? ?方法get()和null

public class Run {private static ThreadLocal tl = new ThreadLocal();public static void main(String[] args) {if(tl.get() == null){System.out.println("從未放過值");tl.set("我的值");}System.out.println(tl.get());System.out.println(tl.get());} }

解決get()返回null問題

public class ThreadLocalExt extends ThreadLocal{@Overrideprotected Object initialValue() {return "我是默認值,第一次get不再為null";} }public class Run {private static ThreadLocalExt tl = new ThreadLocalExt();public static void main(String[] args) {if(tl.get() == null){System.out.println("從未放過值");tl.set("我的值");}System.out.println(tl.get());System.out.println(tl.get());} }

?

?線程變量的隔離性

public class Tools {public static ThreadLocal tl = new ThreadLocal(); }public class ThreadA extends Thread{@Overridepublic void run() {try {for (int i = 0; i < 100; i++) {Tools.tl.set("ThreadA"+(i+1));System.out.println("ThreadA get value="+Tools.tl.get());Thread.sleep(200);}} catch (InterruptedException e) {e.printStackTrace();}} }public class ThreadB extends Thread{@Overridepublic void run() {try {for (int i = 0; i < 100; i++) {Tools.tl.set("ThreadB"+(i+1));System.out.println("ThreadB get value="+Tools.tl.get());Thread.sleep(200);}} catch (InterruptedException e) {e.printStackTrace();}} }public class Run {public static void main(String[] args) {try {ThreadA a = new ThreadA();ThreadB b = new ThreadB();a.start();b.start();for (int i = 0; i < 100; i++) {Tools.tl.set("main"+(i+1));System.out.println("main get value="+Tools.tl.get());Thread.sleep(200);}} catch (InterruptedException e) {e.printStackTrace();}} }

總結

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