ThreadLocal 线程局部变量

ThreadLocal类:

该类提供了线程局部变量,它是一个池 Map<Thread.currentThread,locObj>，

池中为每个线程保存一个独立的局部变量，

每个线程可以从这个池中读取或设置自己的局部变量。

public class ThreadLocalDemo {
  //线程局部变量池
  //private static ThreadLocal<Object> t = new ThreadLocal<Object>();
  private static MyThreadLocal<Object> t=new MyThreadLocal<Object>();
  
  public static Object getValue(){
    //System.out.println(Thread.currentThread());
    Object obj=t.get();
    if(obj==null){
      System.out.println("没有....");
      Random r=new Random();
      obj=r.nextInt(100);
      t.set(obj);
    }
    return obj;
  }
}

这里用自己写的一个类当做ThreadLoacal;

package cn.hncu.ThreadLoc;

import java.util.HashMap;
import java.util.Map;

public class MyThreadLocal<T> {
   
   private Map<Thread,Object> map=new HashMap<Thread, Object>();
   
   public Object get(){
      Thread curThread =Thread.currentThread();
      return map.get(curThread);
   }
   
   public Object set(Object obj){
      Thread curThread=Thread.currentThread();
      return map.put(curThread, obj);
   }
}

测试类：

package cn.hncu.ThreadLoc;

public class Hello {
  public void aaa(){
    Object obj3 = ThreadLocalDemo.getValue();
    System.out.println("obj3:"+obj3);
  }
  public void bbb(){
    Object obj5 = ThreadLocalDemo.getValue();
    System.out.println("obj5:"+obj5);
  }
}


package cn.hncu.ThreadLoc;

import org.junit.Test;

public class ThreadLocTest {
  @Test
  public void demo1() {
    System.out.println(Thread.currentThread());
    Object obj1 = ThreadLocalDemo.getValue();
    Object obj2 = ThreadLocalDemo.getValue();
    System.out.println(obj1 + "," + obj2);
    System.out.println(obj1 == obj2);// true
  }

  @Test
  public void demo2() {
    // System.out.println(Thread.currentThread());
    Object obj1 = ThreadLocalDemo.getValue();
    Object obj2 = ThreadLocalDemo.getValue();
    System.out.println("obj1:" + obj1);
    System.out.println("obj2:" + obj2);
    System.out.println(obj1 == obj2); // true
    new Hello().aaa();
    
    new Thread() {

      /* (non-Javadoc)
       * @see java.lang.Thread#run()
       */
      @Override
      public void run() {
        Object obj4 = ThreadLocalDemo.getValue();
        System.out.println("obj4:"+obj4);
        new Hello().bbb();
      }
       
    }.start();
  }

}

demo1：

demo2: