多线程面试题1

题目：自定义容器，提供新增元素（add）和获取元素数量（size）方法。
启动两个线程。线程1向容器中新增10个数据。线程2监听容器元素数量，当容器元素数量为5时，线程2输出信息并终止。

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 使用三种方法：volatile,    synchronized,    CountDownLatch(门闩)

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1.使用volatile修饰容器，只能保证容器数据的可见性保证不了完整性

public class TestBinFa2  {
	public static void main(String[] args) {
		final Test_01_Container t = new Test_01_Container();
		new Thread(new Runnable() {
			@Override
			public void run() {
				for(int i = 0; i < 50; i++){
					System.out.println(" ");
					System.out.println("前=======>"+t.container.toString());
					t.add(new Integer(i));
					System.out.println("后=======>"+t.container.toString());
					try {
						TimeUnit.SECONDS.sleep(1);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
				}
			}
		}).start();
		
		new Thread(new Runnable(){
			@Override
			public void run() {
				while(true){
					try {
						TimeUnit.SECONDS.sleep(1);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
					System.out.println("长度为=========>"+t.size());
					if(t.size() == 45){
						System.out.println("长度为=========>"+t.size()+"线程2中断了=======");
						break;
					}
				}
			}
		}).start();
	}
}
class Test_01_Container{
	volatile List<Integer> container = new ArrayList<>();
	public /*synchronized*/ void add(int num){
		this.container.add(num);
	}
	public /*synchronized*/ int size(){
		return this.container.size();
	}
}

2.synchronized能保证数据的同步和并发，

public class TestBinFa3  {
	public static void main(String[] args) {
		final Test_01_Container1 t = new Test_01_Container1();
		final Object lock = new Object();
		new Thread(new Runnable() {
			@Override
			public void run() {
				synchronized (lock) {
					for(int i = 0; i < 10; i++){
						
						System.out.println(" ");
						System.out.println("前=======>"+t.container.toString());
						t.add(new Integer(i));
						System.out.println("后=======>"+t.container.toString());
						if(t.size()==5){
							lock.notifyAll();
							try {	
								
								lock.wait();
								Thread.sleep(500);
							} catch (InterruptedException e) {
								e.printStackTrace();
							}
						}
					}
				}
			}
		}).start();
		
		new Thread(new Runnable(){
			@Override
			public void run() {
				synchronized (lock) {
					while(true){
							System.out.println("长度为=========>"+t.size());
							if(t.size() != 5){
								try {
									lock.wait();////当前线程进入等待
									Thread.sleep(500);
								} catch (InterruptedException e) {
									// TODO Auto-generated catch block
									e.printStackTrace();
								}
							}
							System.out.println("长度为=========>"+t.size()+"被中断");
							lock.notifyAll();
							break;
							
					}
				}
			}
		}).start();
	}
}

class Test_01_Container1{
	 List<Integer> container = new ArrayList<>();
	
	public  void add(int num){
		this.container.add(num);
	}
	
	public  int size(){
		return this.container.size();
	}
}

3.使用门闩的方法，当add完后长度为5，就释放门闩，减掉门闩使其开放，

当检测长度不为5则等待门闩，

public class TestBinFa4  {
	public static void main(String[] args) {
		final Test_01_Container2 t = new Test_01_Container2();
		final CountDownLatch latch = new CountDownLatch(1);
		new Thread(new Runnable() {
			@Override
			public void run() {
				for(int i = 0; i < 10; i++){
					System.out.println(" ");
					System.out.println("前=======>"+t.container.toString());
					t.add(new Integer(i));
					System.out.println("后=======>"+t.container.toString());
					if(t.size()==5){
						latch.countDown();////////释放门闩的
						try {	
							Thread.sleep(500);
						} catch (InterruptedException e) {
							e.printStackTrace();
						}
					}
				}
			}
		}).start();
		
		new Thread(new Runnable(){
			@Override
			public void run() {
					while(true){
						System.out.println("长度为=========>"+t.size());
						if(t.size() != 5){
							try {
								latch.await();////等待门闩个数为0就能往下运行。
								Thread.sleep(500);
							} catch (InterruptedException e) {
								// TODO Auto-generated catch block
								e.printStackTrace();
							}
						}
						System.out.println("长度为=========>"+t.size()+"被中断");
						break;
					}
			}
		}).start();
	}
}
class Test_01_Container2{
	 List<Integer> container = new ArrayList<>();
	public  void add(int num){
		this.container.add(num);
	}
	public  int size(){
		return this.container.size();
	}
}