类ThreadLocal主要解决的就是每个线程绑定自己的值,可以将ThreadLocal类比喻成全局存放数据的盒子,盒子中可以存储每个线程的私有数据。
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("从未放过值");
tl.set("我的值");
}
System.out.println(tl.get());
System.out.println(tl.get());
}
}
解决get()返回null问题
public class ThreadLocalExt extends ThreadLocal{
@Override
protected Object initialValue() {
return "我是默认值,第一次get不再为null";
}
}
public class Run {
private static ThreadLocalExt tl = new ThreadLocalExt();
public static void main(String[] args) {
if(tl.get() == null){
System.out.println("从未放过值");
tl.set("我的值");
}
System.out.println(tl.get());
System.out.println(tl.get());
}
}
线程变量的隔离性
public class Tools {
public static ThreadLocal tl = new ThreadLocal();
}
public class ThreadA extends Thread{
@Override
public 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{
@Override
public 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();
}
}
}