引言

摳Thread類所有公有的方法和實現。

執行緒的狀態:內部列舉類State

public enum State {
        /**
         * Thread state for a thread which has not yet started.
         */
        NEW,

        /**
         * Thread state for a runnable thread.  A thread in the runnable
         * state is executing in the Java virtual machine but it may
         * be waiting for other resources from the operating system
         * such as processor.
         */
        RUNNABLE,

        /**
         * Thread state for a thread blocked waiting for a monitor lock.
         * A thread in the blocked state is waiting for a monitor lock
         * to enter a synchronized block/method or
         * reenter a synchronized block/method after calling
         * {@link Object#wait() Object.wait}.
         */
        BLOCKED,

        /**
         * Thread state for a waiting thread.
         * A thread is in the waiting state due to calling one of the
         * following methods:
         * <ul>
         *   <li>{@link Object#wait() Object.wait} with no timeout</li>
         *   <li>{@link #join() Thread.join} with no timeout</li>
         *   <li>{@link LockSupport#park() LockSupport.park}</li>
         * </ul>
         *
         * <p>A thread in the waiting state is waiting for another thread to
         * perform a particular action.
         *
         * For example, a thread that has called <tt>Object.wait()</tt>
         * on an object is waiting for another thread to call
         * <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
         * that object. A thread that has called <tt>Thread.join()</tt>
         * is waiting for a specified thread to terminate.
         */
        WAITING,

        /**
         * Thread state for a waiting thread with a specified waiting time.
         * A thread is in the timed waiting state due to calling one of
         * the following methods with a specified positive waiting time:
         * <ul>
         *   <li>{@link #sleep Thread.sleep}</li>
         *   <li>{@link Object#wait(long) Object.wait} with timeout</li>
         *   <li>{@link #join(long) Thread.join} with timeout</li>
         *   <li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
         *   <li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
         * </ul>
         */
        TIMED_WAITING,

        /**
         * Thread state for a terminated thread.
         * The thread has completed execution.
         */
        TERMINATED;
    }

    /**
     * Returns the state of this thread.
     * This method is designed for use in monitoring of the system state,
     * not for synchronization control.
     *
     * @return this thread's state.
     * @since 1.5
     */
    public State getState() {
        // get current thread state
        return sun.misc.VM.toThreadState(threadStatus);
    }

需要關注一個常常被忽略的方法

   public static native boolean holdsLock(Object obj);

判斷當前執行緒是否持有鎖。

狀態變化的幾個方法

這幾個方法比較常見就不解釋了~

yield()
sleep(long millis)
sleep(long millis, int nanos)
start()
join(long)
join(long, int)
join()
run()
isAlive()

這幾個解釋一下：

interrupt(): 執行緒例項請求中斷
isInterrupted(): 返回執行緒例項是否中斷
interrupted(): 當前執行緒(currentThread方法)是否中斷

初始化

初始化主要了解兩個方法：

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

public Thread(ThreadGroup group, Runnable target, String name,long stackSize) {
	init(group, target, name, stackSize);
}

其餘過載方法就是前三個引數的組合。

這裡我們不擴充講init方法，init方法將新執行緒和當前執行緒的絕大多數屬性都設定為一致。

這裡講一下未指定執行緒名時會設定為"Thread-" + nextThreadNum()，而nextThreadNum是一個同步的方法：

    /* For autonumbering anonymous threads. */
    private static int threadInitNumber;
    private static synchronized int nextThreadNum() {
        return threadInitNumber++;
    }

需要注意的是，這個是隻針對匿名初始化執行緒的！看下面的程式碼：

//原本的		
System.out.println(new Thread().getName()); //Thread-0
System.out.println(new Thread().getName()); //Thread-1
System.out.println(new Thread().getName()); //Thread-2
//修改了中間的構造方法
System.out.println(new Thread().getName()); //Thread-0
System.out.println(new Thread("mid").getName()); //mid
System.out.println(new Thread().getName()); //Thread-1

一些其他獲取屬性的方法：

setPriority(int)
getPriority()
setName(String name)
getName()
getThreadGroup()
setDaemon(boolean isDaemon)
isDaemon()
getId()
getState()

Thread類中所有一些和ThreadGroup相關的方法：

activeCount() 獲取當前執行緒組中存活的執行緒數量
enumerate(Thread[] tarray) 獲取執行緒組的後輩執行緒數量

異常相關Debug相關

Thread中有一個和異常相關函式介面，當執行緒由於異常終止時不會觸發JVM的異常終止，而是會呼叫該介面的方法。

	@FunctionalInterface
    public interface UncaughtExceptionHandler {
        /**
         * Method invoked when the given thread terminates due to the
         * given uncaught exception.
         * <p>Any exception thrown by this method will be ignored by the
         * Java Virtual Machine.
         * @param t the thread
         * @param e the exception
         */
        void uncaughtException(Thread t, Throwable e);
    }

例如：
原本會觸發JVM的異常機制：

	public static void main(String[] args){
        Thread thread1 = new Thread(()->{
            throw new IllegalArgumentException("bug");
        });

        thread1.start();
    }
    // Exception in thread "Thread-0" java.lang.IllegalArgumentException: bug

修改後：

	public static void main(String[] args){
        Thread thread1 = new Thread(()->{
            throw new IllegalArgumentException("bug");
        });

        thread1.setUncaughtExceptionHandler((Thread thread, Throwable throwable)->{
            System.out.println("hhhh");
        });

        thread1.start();
    }
    //最終列印 hhhh

相應的有些方法：

setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler eh)
getDefaultUncaughtExceptionHandler
getUncaughtExceptionHandler
setUncaughtExceptionHandler(UncaughtExceptionHandler eh)

還有一些debug的方法也不介紹了：

getStackTrace
getAllStackTraces
checkAccess
dumpStack

上下文

setContextClassLoader(ClassLoader cl)方法和getContextClassLoader()通過下面這個例子理解~

public class SetContextLoader implements Runnable {

	Thread thread;

	public SetContextLoader() {
		thread = new Thread(this);
		thread.start();
	}

	public void run() {
		ClassLoader classLoader = thread.getContextClassLoader();
		/* Sets the context ClassLoader for this Thread. */
		thread.setContextClassLoader(ClassLoader.getSystemClassLoader());
		System.out.println("Class - " + classLoader.getClass());
		System.out.println("Parent- " + classLoader.getParent());
	
	}

	public static void main(String args[]) {
		new SetContextLoader();
	}
}

輸出：

Class - class sun.misc.Launcher$AppClassLoader
Parent- sun.misc.Launcher$ExtClassLoader@757aef