ThreadLocal: each thread its own local memory, local area, similar to the container, in which each thread will have some storage space
commonly used methods get / set / initialValue
official advice to private static
each thread to store their data, not change will affect the other thread
ThreadLocal subclass InheritableThreadLocal:
data context of inheritance
public class my {
//Integer 初始值为null
//private static ThreadLocal<Integer> threadlocal=new ThreadLocal<>();
//更改初始值需要创建ThreadLocal的子类重写initialValue或者使用lambda(jdk8)
private static ThreadLocal<Integer> threadlocal=new ThreadLocal <Integer>()
{//父类匿名内部类重写方法
protected Integer initialValue()
{
return 200;
}
};
//private static ThreadLocal<Integer> threadlocal=new ThreadLocal.withInitial(()->200);
public static void main(String[]args) throws InterruptedException
{
//获取值
System.out.println(Thread.currentThread().getName()+"-->"+threadlocal.get());
//设置值
threadlocal.set(99);
System.out.println(Thread.currentThread().getName()+"-->"+threadlocal.get());
new Thread(new test()).start();
new Thread(new test()).start();
}
public static class test implements Runnable
{
public void run()
{
threadlocal.set((int)(Math.random()*100));
System.out.println(Thread.currentThread().getName()+"-->"+threadlocal.get());
}
}
}
Each thread its own data changes do not affect other threads
public class my {
private static ThreadLocal<Integer> threadlocal=new ThreadLocal <Integer>()
{//父类匿名内部类重写方法
protected Integer initialValue()
{
return 1;
}
};
public static void main(String[]args) throws InterruptedException
{
for(int i=0;i<5;i++)
{
new Thread(new test()).start();
}
}
public static class test implements Runnable
{
public void run()
{
//修改不会影响其他线程
Integer left=threadlocal.get();
System.out.println(Thread.currentThread().getName()+"-->"+left);
threadlocal.set(left-1);
System.out.println(Thread.currentThread().getName()+"还剩下"+threadlocal.get());
}
}
}
Analysis ThreadLocal operating environment:
public class my {
private static ThreadLocal<Integer> threadlocal=new ThreadLocal <Integer>()
{//父类匿名内部类重写方法
protected Integer initialValue()
{
return 1;
}
};
public static void main(String[]args) throws InterruptedException
{
new Thread(new test()).start();//两个打印的内容在不同的线程里
//当start()之后,线程才从main转换到其他线程,所以构造器里的是main线程的
}
public static class test implements Runnable
{
public test()
{
threadlocal.set(100); //属于main线程,修改不会影响start内的线程
System.out.println(Thread.currentThread().getName()+"-->"+threadlocal.get());
}
public void run()
{
System.out.println(Thread.currentThread().getName()+"还剩下"+threadlocal.get());
}
}
}
子类InheritableThreadLocal:
public class my {
private static ThreadLocal<Integer> threadlocal=new InheritableThreadLocal<>();
public static void main(String[]args) throws InterruptedException
{
System.out.println(Thread.currentThread().getName()+"-->"+threadlocal.get());
threadlocal.set(2);
//此线程由main线程开辟,拷贝一份main线程的数据给此线程
//即将main线程里的2给此线程
new Thread(()->{
System.out.println(Thread.currentThread().getName()+"-->"+threadlocal.get());
threadlocal.set(200);
System.out.println(Thread.currentThread().getName()+"-->"+threadlocal.get());
}).start();
}
}