/* * Copyright (c) 2000 David Flanagan.  All rights reserved. * This code is from the book Java Examples in a Nutshell, 2nd Edition. * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied. * You may study, use, and modify it for any non-commercial purpose. * You may distribute it non-commercially as long as you retain this notice. * For a commercial use license, or to purchase the book (recommended), * visit http://www.davidflanagan.com/javaexamples2. */package com.davidflanagan.examples.thread;import java.io.*;import java.awt.*;     // AWT classes for the demo programimport javax.swing.*;  // Swing GUI classes for the demo/** * This class contains a useful static method for listing all threads * and threadgroups in the VM.  It also has a simple main() method so it * can be run as a standalone program. **/public class ThreadLister {    /** Display information about a thread. */    private static void printThreadInfo(PrintWriter out, Thread t, 					String indent) {        if (t == null) return;        out.println(indent + "Thread: " + t.getName() +		    "  Priority: " + t.getPriority() +		    (t.isDaemon()?" Daemon":"") +		    (t.isAlive()?"":" Not Alive"));    }        /** Display info about a thread group and its threads and groups */    private static void printGroupInfo(PrintWriter out, ThreadGroup g, 				       String indent) {        if (g == null) return;        int num_threads = g.activeCount();        int num_groups = g.activeGroupCount();        Thread[] threads = new Thread[num_threads];        ThreadGroup[] groups = new ThreadGroup[num_groups];                g.enumerate(threads, false);        g.enumerate(groups, false);                out.println(indent + "Thread Group: " + g.getName() + 		    "  Max Priority: " + g.getMaxPriority() +		    (g.isDaemon()?" Daemon":""));                for(int i = 0; i < num_threads; i++)            printThreadInfo(out, threads[i], indent + "    ");        for(int i = 0; i < num_groups; i++)            printGroupInfo(out, groups[i], indent + "    ");    }        /** Find the root thread group and list it recursively */    public static void listAllThreads(PrintWriter out) {        ThreadGroup current_thread_group;        ThreadGroup root_thread_group;        ThreadGroup parent;                // Get the current thread group        current_thread_group = Thread.currentThread().getThreadGroup();                // Now go find the root thread group        root_thread_group = current_thread_group;        parent = root_thread_group.getParent();        while(parent != null) {            root_thread_group = parent;            parent = parent.getParent();        }                // And list it, recursively        printGroupInfo(out, root_thread_group, "");    }        /**     * The main() method create a simple graphical user interface to display     * the threads in.  This allows us to see the "event dispatch thread" used     * by AWT and Swing.     **/    public static void main(String[] args) {	// Create a simple Swing GUI	JFrame frame = new JFrame("ThreadLister Demo");	JTextArea textarea = new JTextArea();	frame.getContentPane().add(new JScrollPane(textarea),				   BorderLayout.CENTER);	frame.setSize(500, 400);	frame.setVisible(true);	// Get the threadlisting as a string using a StringWriter stream	StringWriter sout = new StringWriter();  // To capture the listing 	PrintWriter out = new PrintWriter(sout);	ThreadLister.listAllThreads(out);        // List threads to stream	out.close();                             	String threadListing = sout.toString();  // Get listing as a string	// Finally, display the thread listing in the GUI	textarea.setText(threadListing);    }}