理由听我慢慢道来。官方权威文档『The Java Language Specification』,JLS7,Chapter 17 Threads and Locks (p563),开篇第二段明确指出:

Threads are represented by the Thread.class. The only way for a user to create a thread is to create an object of this class; each thread is associated with such an object. A thread will start when the start() method is invoked on the corresponding Thread object.



第一本:『Java Performance,Chapter 3 JVM Overview,HotSpot VM Runtime,Thread Creation and Destruction (p73) 指出。

There are two ways for a thread to be introduced in the HotSpot VM; either by exe-cuting Java code that calls the start() method on a java.lang.Thread object, or by attaching an existing native thread to the HotSpot VM using JNI.

文中说,创建一个HotSpot VM(注意其它VM不一定适用)线程有两种方法:

  1. 创建一个java.lang.Thread对象,并调用其start()方法
  2. 通过本地方法(如JNI)创建本地线程并加入的HotSpot VM中

第二本:『Java 7 Concurrency Cookbook,Chapter 1 Thread Management,Creating and running a thread 则这么说。

As with every element in the Java language, threads are objects. We have two ways of creating a thread in Java:

  • Extending the Thread class and overriding the run() method
  • Building a class that implements the Runnable interface and then creating an object of the Thread class passing the Runnable object as a parameter

第三本:『The Java TutorialsEssential Java ClassesConcurrencyDefining and Starting a Thread中。

An application that creates an instance of Thread must provide the code that will run in that thread. There are two ways to do this:

  • Provide a Runnable object. The Runnable interface defines a single method, run, meant to contain the code executed in the thread. The Runnable object is passed to the Thread constructor, as in the HelloRunnable example:

    public class HelloRunnable implements Runnable {
    public void run() {
    System.out.println("Hello from a thread!");
    public static void main(String args[]) {
    (new Thread(new HelloRunnable())).start();
  • Subclass Thread. The Thread class itself implements Runnable, though its run method does nothing. An application can subclass Thread, providing its own implementation of run, as in the HelloThread example:

    public class HelloThread extends Thread {
    public void run() {
    System.out.println("Hello from a thread!");
    public static void main(String args[]) {
    (new HelloThread()).start();

Notice that both examples invoke Thread.start in order to start the new thread.

Which of these idioms should you use? The first idiom, which employs a Runnable object, is more general, because the Runnable object can subclass a class other than Thread. The second idiom is easier to use in simple applications, but is limited by the fact that your task class must be a descendant of Thread.

如上两本书的说法应该是大多说人一致认为的正确答案:继承Thread类或实现Runnable接口。同时The Java Tutorials还指出了使用哪种方式创建线程更好。

我认为后两本书的说法只能算是创建线程的两种写法,归根结底都必须create Thread object。我更认可JLS的说法,它是无可争辩的权威。另外还有一些更乱七八糟的说法如executor framework也算一种方法,这样算起来就太多了。在目前的Hotspot JDK 7中,java.lang.Thread有8个public构造函数:

public java.lang.Thread.Thread()
public java.lang.Thread.Thread(Runnable)
public java.lang.Thread.Thread(ThreadGroup, Runnable)
public java.lang.Thread.Thread(String)
public java.lang.Thread.Thread(ThreadGroup, String)
public java.lang.Thread.Thread(Runnable, String)
public java.lang.Thread.Thread(ThreadGroup, Runnable, String)
public java.lang.Thread.Thread(ThreadGroup, Runnable, String, long)


java.lang.Thread.Thread(Runnable, AccessControlContext)