Java Java.lang.ThreadLocal用法及代码示例

该类提供线程局部变量。这些变量与其正常对应变量的不同之处在于，访问一个变量(通过其 get 或 set 方法)的每个线程都有其自己的、独立初始化的变量副本。本质上，这是除了编写不可变类之外实现线程安全的另一种方法。由于对象不再共享，因此不需要同步，这可以提高应用程序的可扩展性和性能。 ThreadLocal提供线程限制，它是局部变量的扩展。 ThreadLocal仅在单个线程中可见。没有两个线程可以看到彼此的线程局部变量。这些变量通常是类中的私有静态字段，并在线程内维护它们的状态。

Note: ThreadLocal class extends Object class

构造函数：ThreadLocal()：这将创建一个线程局部变量。

ThreadLocal类的方法

方法	执行的操作
get()	返回此线程局部变量的当前线程副本中的值。如果该变量对于当前线程没有值，则首先将其初始化为调用 initialValue() 方法返回的值
initialValue()	返回本地线程变量的当前线程初始值。
remove()	删除此线程局部变量的当前线程值。如果当前线程随后读取此线程局部变量，则将通过调用其 initialValue() 方法重新初始化其值，除非当前线程在此期间设置其值。这可能会导致当前线程中多次调用initialValue方法
set()	将此线程局部变量的当前线程副本设置为指定值。大多数子类不需要重写此方法，仅依靠initialValue()方法来设置线程局部变量的值。

示例 1：

Java


// Java Program to Illustrate ThreadLocal Class
// Via get() and set() Method
// Class
// ThreadLocalDemo
class GFG {
    // Main driver method
    public static void main(String[] args)
    {
        // Creating objects of ThreadLocal class
        ThreadLocal<Number> gfg_local
            = new ThreadLocal<Number>();
        ThreadLocal<String> gfg = new ThreadLocal<String>();
        // Now setting custom value
        gfg_local.set(100);
        // Returns the current thread's value
        System.out.println("value = " + gfg_local.get());
        // Setting the value
        gfg_local.set(90);
        // Returns the current thread's value of
        System.out.println("value = " + gfg_local.get());
        // Setting the value
        gfg_local.set(88.45);
        // Returns the current thread's value of
        System.out.println("value = " + gfg_local.get());
        // Setting the value
        gfg.set("GeeksforGeeks");
        // Returning the current thread's value of
        System.out.println("value = " + gfg.get());
    }
}

输出

value = 100
value = 90
value = 88.45
value = GeeksforGeeks

示例 2：

Java


// Java Program to Illustrate ThreadLocal Class
// Via Illustrating remove() Method
// Class
// ThreadLocalDemo
public class GFG {
    // Main driver method
    public static void main(String[] args)
    {
        // Creating objects of ThreadLocal class
        ThreadLocal<Number> gfg_local
            = new ThreadLocal<Number>();
        ThreadLocal<String> gfg = new ThreadLocal<String>();
        // Setting the value
        gfg_local.set(100);
        // Returning the current thread's value
        System.out.println("value = " + gfg_local.get());
        // Setting the value
        gfg_local.set(90);
        // Returns the current thread's value of
        System.out.println("value = " + gfg_local.get());
        // Setting the value
        gfg_local.set(88.45);
        // Returning the current thread's value of
        System.out.println("value = " + gfg_local.get());
        // Setting the value
        gfg.set("GeeksforGeeks");
        // Returning the current thread's value of
        System.out.println("value = " + gfg.get());
        // Removing value using remove() method
        gfg.remove();
        // Returning the current thread's value of
        System.out.println("value = " + gfg.get());
        // Removing value
        gfg_local.remove();
        // Returns the current thread's value of
        System.out.println("value = " + gfg_local.get());
    }
}

输出

value = 100
value = 90
value = 88.45
value = GeeksforGeeks
value = null
value = null

示例 3：

Java


// Java Program to Illustrate ThreadLocal Class
// Via initialValue() Method
// Importing required classes
import java.lang.*;
// Class 1
// Helper class extending Thread class
class NewThread extends Thread {
    private static ThreadLocal gfg = new ThreadLocal() {
        protected Object initialValue()
        {
            return new Integer(question--);
        }
    };
    private static int question = 15;
    NewThread(String name)
    {
        // super keyword refers to parent class instance
        super(name);
        start();
    }
    // Method
    // run() method for Thread
    public void run()
    {
        for (int i = 0; i < 2; i++)
            System.out.println(getName() + " " + gfg.get());
    }
}
// Class 2
// Main class
// ThreadLocalDemo
public class GFG {
    // Main driver method
    public static void main(String[] args)
    {
        // Creating threads inside main() method
        NewThread t1 = new NewThread("quiz1");
        NewThread t2 = new NewThread("quiz2");
    }
}

输出：

相关用法

注：本文由纯净天空筛选整理自佚名大神的英文原创作品 Java.lang.ThreadLocal Class in Java。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。