线程实现方式extends Thread 和 implements Runnable

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• 线程安全：当多个线程访问同一个类时，这个类始终表现出正确的行为
• synchronized ：可在任意方法或对象上加锁

  一.extends Thread

package com.zan;

public class TestThread extends Thread{

    private int count = 5 ;
	
	//synchronized加锁 ，实现线程同步
    //加锁的这段代码称为：互斥区或临界区
	public void run(){  //也可在直接方法上加synchronized 
		synchronized (this) {			
			count--;
			System.out.println("线程"+currentThread().getName() + " count--> "+ count);
		}
	}
	
	public static void main(String[] args) {
		/**
		 *     当多个线程访问TestThread的run方法时，以排队的方式进行处理（这里排对是按照CPU分配的先后顺序而定的），
		 * 		一个线程想要执行synchronized修饰的方法里的代码：
		 * 		1 首先要获得锁
		 * 		2 若是拿到锁，执行synchronized代码体内容；拿不到锁，这个线程就会不断的尝试获得这把锁，直到拿到为止，
		 * 		   而且是多个线程同时去竞争这把锁。（也就是会有锁竞争的问题）
		 */
		TestThread thread = new TestThread();
		Thread t1 = new Thread(thread,"t1");
		Thread t2 = new Thread(thread,"t2");
		Thread t3 = new Thread(thread,"t3");
		Thread t4 = new Thread(thread,"t4");
		Thread t5 = new Thread(thread,"t5");
		t1.start();
		t2.start();
		t3.start();
		t4.start();
		t5.start();
	
	}
}

 

二.implements Runnable

 

package com.zan;

public class TestThread2 implements Runnable{

	private int count = 5 ;
	@Override
	public synchronized void run() {
		count--;
		System.out.println("线程"+Thread.currentThread().getName() + " count--> "+ count);
	}
	
	public static void main(String[] args) {
		
		TestThread2 thread = new TestThread2();
		Thread t1 = new Thread(thread,"t1");
		Thread t2 = new Thread(thread,"t2");
		Thread t3 = new Thread(thread,"t3");
		Thread t4 = new Thread(thread,"t4");
		Thread t5 = new Thread(thread,"t5");
		t1.start();
		t2.start();
		t3.start();
		t4.start();
		t5.start();
	
	}

}

 

Runnable比Thread好：1.适合资源共享  2.java只能单继承，但可以实现多个接口。避免继承的局限