1 public interface Runnable {
2     public abstract void run();
3 }

1 public class Thread implements Runnable{
2
3 }

1 public Thread() {
2     init(null, null, "Thread-" + nextThreadNum(), 0);
3 }

1 public Thread(Runnable target) {
2     init(null, target, "Thread-" + nextThreadNum(), 0);
3 }

1 public Thread(ThreadGroup group, Runnable target) {
2     init(group, target, "Thread-" + nextThreadNum(), 0);
3 }

1 public Thread(String name) {
2     init(null, null, name, 0);
3 }　　　　　　　　　　　　　　　　　　还有其它的构造方法，此处省略。。。

 1 /**
 2      * Initializes a Thread.
 3      *
 4      * @param g the Thread group
 5      * @param target the object whose run() method gets called
 6      * @param name the name of the new Thread
 7      * @param stackSize the desired stack size for the new thread, or
 8      *        zero to indicate that this parameter is to be ignored.
 9      */　　　　//ThreadGroup：线程组表示一个线程的集合。此外，线程组也可以包含其他线程组。线程组构成一棵树，在树中，除了初始线程组外，每个线程组都有一个父线程组。 
10     private void init(ThreadGroup g, Runnable target, String name,
11                       long stackSize) {
12     Thread parent = currentThread();
13     SecurityManager security = System.getSecurityManager();
14     if (g == null) {
15         /* Determine if it's an applet or not */
16
17         /* If there is a security manager, ask the security manager
18            what to do. */
19         if (security != null) {
20         g = security.getThreadGroup();
21         }
22
23         /* If the security doesn't have a strong opinion of the matter
24            use the parent thread group. */
25         if (g == null) {
26         g = parent.getThreadGroup();
27         }
28     }
29
30     /* checkAccess regardless of whether or not threadgroup is
31            explicitly passed in. */
32     g.checkAccess();
33
34     /*
35      * Do we have the required permissions?
36      */
37     if (security != null) {
38         if (isCCLOverridden(getClass())) {
39             security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
40         }
41     }
42
43
44         g.addUnstarted();
45
46     this.group = g;

　　　　//每个线程都有一个优先级，高优先级线程的执行优先于低优先级线程。每个线程都可以或不可以标记为一个守护程序。当某个线程中运行的代码创建一个新 Thread 对象时，该新线程的初始优先级被设定为创建线程的优先级，并且当且仅当创建线程是守护线程时，新线程才是守护程序。 

47     this.daemon = parent.isDaemon();
48     this.priority = parent.getPriority();
49     this.name = name.toCharArray();
50     if (security == null || isCCLOverridden(parent.getClass()))
51         this.contextClassLoader = parent.getContextClassLoader();
52     else
53         this.contextClassLoader = parent.contextClassLoader;
54     this.inheritedAccessControlContext = AccessController.getContext();
55     this.target = target;
56     setPriority(priority);
57         if (parent.inheritableThreadLocals != null)
58         this.inheritableThreadLocals =
59         ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
60         /* Stash the specified stack size in case the VM cares */
61         this.stackSize = stackSize;
62
63         /* Set thread ID */
64         tid = nextThreadID();
65     }

 1 public synchronized void start() {
 2         /**
 3      * This method is not invoked for the main method thread or "system"
 4      * group threads created/set up by the VM. Any new functionality added
 5      * to this method in the future may have to also be added to the VM.
 6      *
 7      * A zero status value corresponds to state "NEW".
 8          */
 9         if (threadStatus != 0)
10             throw new IllegalThreadStateException();
11         group.add(this);
12         start0();
13         if (stopBeforeStart) {
14         stop0(throwableFromStop);
15     }
16 }

 1 private native void start0();

1 public void run() {
2     if (target != null) {
3         target.run();
4     }
5 }

1 private Runnable target;

1 public Thread(Runnable target) {
2     init(null, target, "Thread-" + nextThreadNum(), 0);
3 }