void setDaemon(boolean on) 
          将该线程标记为守护线程或用户线程。 

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设置为守护线程的线程,将会在其他非守护线程结束后停止执行,但会挣扎一瞬间

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		Thread t1 = new Thread() {
			@Override
			public void run() {
				for (int i = 0; i < 1000; i++) {
					System.out.println("aa" + i);
				}
			}
		};
		Thread t2 = new Thread() {
			@Override
			public void run() {
				for (int i = 0; i < 2; i++) {
					System.out.println("bbbbbbb" + i);
				}
			}
		};
		Thread t3 = new Thread() {
			@Override
			public void run() {
				for (int i = 0; i < 1000; i++) {
					System.out.println("cccc" + i);
				}
			}
		};
		t1.setDaemon(true);
		t1.start();
		t2.start();
		t3.start();