總結(jié)：

1. Static聲明的ThreadLocal修飾的變量，為線程私有顾患，即某個線程修改之后對其他線程沒有影響
2. Static聲明的基本類型變量暇检，為全局共享，即任意一個線程修改之后深寥，對其他線程是可見的攘乒，記得加volatile

如果在ThreadLocal變量前加volatile，不會生效

public class ThreadLocalTest {
        //聲明一個Threadlocal變量惋鹅，包裝的是Boolean類型则酝，初始化false
    static ThreadLocal<Boolean> local = new ThreadLocal<Boolean>(){ 
        @Override
        protected Boolean initialValue() {
            return false;
        }
    };

    private static ThreadLocalTest instance;
    //雙重
    public static ThreadLocalTest getInstance(){
        if(instance==null){
            synchronized (ThreadLocalTest.class) {
                if(instance==null){
                    instance = new ThreadLocalTest();
                }
            }
        }
        return instance;
    }
    
    public void set(boolean value){
        local.set(value);
    }
    
    public boolean get(){
        return local.get();
    }

    public static void main(String[] args) {
        System.out.println(Thread.currentThread().getName()+"："+ThreadLocalTest.getInstance().get());//false
        ThreadLocalTest.getInstance().set(true);
        System.out.println(Thread.currentThread().getName()+"："+ThreadLocalTest.getInstance().get());//true
        
        new Thread(new Runnable() {
            public void run() {
                //ThreadLocalTest.getInstance().set(true);
                System.out.println(Thread.currentThread().getName()+"："+ThreadLocalTest.getInstance().get()); //true
            }
        }).start();
        
        new Thread(new Runnable() {
            public void run() {
                System.out.println(Thread.currentThread().getName()+"："+ThreadLocalTest.getInstance().get());//false
            }
        }).start();
    }
}

public class ThreadLocalTest2 {
    
    static Boolean flag  = false; //將threadlocal變量換成普通類型變量
    
    private static ThreadLocalTest2 instance;
    
    public static ThreadLocalTest2 getInstance(){
        if(instance==null){
            synchronized (ThreadLocalTest2.class) {
                if(instance==null){
                    instance = new ThreadLocalTest2();
                }
            }
        }
        return instance;
    }
    
    public void set(boolean value){
        flag = value;
    }
    
    public boolean get(){
        return flag;
    }

    public static void main(String[] args) {
                //第一次為false，因為默認(rèn)是false
        System.out.println(Thread.currentThread().getName()+"："+ThreadLocalTest2.getInstance().get());//false
        
        //設(shè)置一次之后闰集，全局共享
        ThreadLocalTest2.getInstance().set(true);
        System.out.println(Thread.currentThread().getName()+"："+ThreadLocalTest2.getInstance().get());//true
        
                //該變量對其他線程都是共享的
        new Thread(new Runnable() {
            public void run() {
                //ThreadLocalTest2.getInstance().set(true); //如果將賦值語句放在此處沽讹，將上面的set注釋掉般卑，運行幾次看看結(jié)果是否還一樣
                System.out.println(Thread.currentThread().getName()+"："+ThreadLocalTest2.getInstance().get()); //true
            }
        }).start();
        
        new Thread(new Runnable() {
            public void run() {
                System.out.println(Thread.currentThread().getName()+"："+ThreadLocalTest2.getInstance().get());//true
            }
        }).start();
    }
}