Java ThreadGroup checkAccess()用法及代碼示例

ThreadGroup類checkAccess()方法

• checkAccess() 方法可在java.lang包。
• checkAccess() 方法用於檢查當前運行的線程是否具有更新線程組的權限。
• checkAccess() 方法不是靜態方法，因此不能通過類名訪問(即隻能通過類對象訪問此方法)。
• checkAccess() 方法是 final 方法，因此它不可重寫(即此方法在子類中不可重寫)。
• 該方法可能在訪問線程組時拋出異常。
  SecurityException：在安全管理器存在時當前線程未被授權訪問線程組時的此異常。

用法:

    public final void checkAccess();

參數：

• 此方法不接受任何參數。

返回值：

這個方法的返回類型是void，它不返回任何東西。

例：

// Java program to demonstrate the example of 
// checkAccess () method of ThreadGroup Class.

import java.lang.*;

class CheckAccess extends Thread {
    // Override run() of Thread class
    public void run() {
        String name = Thread.currentThread().getName();
        System.out.println(name + " " + "finish executing");
    }
}

public class Main {
    public static void main(String[] args) {
        CheckAccess ca = new CheckAccess();

        try {
            // We are creating an object of ThreadGroup class
            ThreadGroup tg1 = new ThreadGroup("ThreadGroup 1");
            ThreadGroup tg2 = new ThreadGroup("ThreadGroup 2");

            // We are creating an object of Thread class and 
            // we are assigning the ThreadGroup of both the thread

            Thread th1 = new Thread(tg1, ca, "First Thread");
            Thread th2 = new Thread(tg2, ca, "Second Thread");

            // Calling start() method with Thread class object 
            // of Thread class

            th1.start();
            th2.start();

            // Here we are checking access of ThreadGroup
            try {
                tg1.checkAccess();
                System.out.println(tg1.getName() + " " + "has access");

                tg2.checkAccess();
                System.out.println(tg2.getName() + " " + "has access");

            } catch (SecurityException se) {

                System.out.println(se.getMessage());
            }

            th1.join();
            th2.join();

        } catch (Exception ex) {

            System.out.println(ex.getMessage());
        }
    }
}

輸出

E:\Programs>javac Main.java
E:\Programs>java Main
ThreadGroup 1 has access
ThreadGroup 2 has access
First Thread finish executing
Second Thread finish executing