線程初始化

	private void init(ThreadGroup g, Runnable target, String name,
                      long stackSize, AccessControlContext acc,
                      boolean inheritThreadLocals) {
        if (name == null) {
            throw new NullPointerException("name cannot be null");
        }

        this.name = name;
		//當前線程就是該線程的父線程
        Thread parent = currentThread();
        SecurityManager security = System.getSecurityManager();
        if (g == null) {
            /* Determine if it's an applet or not */

            /* If there is a security manager, ask the security manager
               what to do. */
            if (security != null) {
                g = security.getThreadGroup();
            }

            /* If the security doesn't have a strong opinion of the matter
               use the parent thread group. */
            if (g == null) {
                g = parent.getThreadGroup();
            }
        }

        /* checkAccess regardless of whether or not threadgroup is
           explicitly passed in. */
        g.checkAccess();

        /*
         * Do we have the required permissions?
         */
        if (security != null) {
            if (isCCLOverridden(getClass())) {
                security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);
            }
        }

        g.addUnstarted();

        this.group = g;
        // 將daemon、priority屬性設置爲父線程的對應屬性
        this.daemon = parent.isDaemon();
        this.priority = parent.getPriority();
        if (security == null || isCCLOverridden(parent.getClass()))
            this.contextClassLoader = parent.getContextClassLoader();
        else
            this.contextClassLoader = parent.contextClassLoader;
        this.inheritedAccessControlContext =
                acc != null ? acc : AccessController.getContext();
        this.target = target;
        setPriority(priority);
        // 將父線程的InheritableThreadLocal複製過來
        if (inheritThreadLocals && parent.inheritableThreadLocals != null)
            this.inheritableThreadLocals =
                ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
        /* Stash the specified stack size in case the VM cares */
        this.stackSize = stackSize;

        /* 分配一個線程id */
        tid = nextThreadID();
    }

在上述過程中，一個新構造的線程對象是由其parent線程來進行空間分配的，而
child線程繼承了parent是否爲Daemon、優先級和加載資源的contextClassLoader
以及可繼承的ThreadLoacl,同時還會分配一個唯一的ID來標識這個child線程。
至此，一個能夠運行的 線程對象就初始化好了，在堆內存中等待這運行。

線程對象在初始化完成之後，調用start(）方法就可以啓動這個線程。
線程start(）方法的含義是：當前線程（即parent線程）同步告知Java虛擬機，只要線程規劃空閒，應立即啓動調用start(）方法的線程