java关于多线程的面试题(三道)--参考答案

第一题参考答案

public class Test {
	
	public static void main(String[] args){
        final BlockingQueue<String> queue = new ArrayBlockingQueue<String>(1);
		for(int i=0;i<4;i++){
			new Thread(new Runnable(){
				@Override
				public void run() {
					while(true){
						try {
							String log = queue.take();
							parseLog(log);
						} catch (InterruptedException e) {
							// TODO Auto-generated catch block
							e.printStackTrace();
						}
					}
				}
				
			}).start();
		}
		
		System.out.println("begin:"+(System.currentTimeMillis()/1000));
		/*模拟处理16行日志，下面的代码产生了16个日志对象，当前代码需要运行16秒才能打印完这些日志。
		修改程序代码，开四个线程让这16个对象在4秒钟打完。
		*/
		for(int i=0;i<16;i++){  //这行代码不能改动
			final String log = ""+(i+1);//这行代码不能改动
			{
					try {
						queue.put(log);
					} catch (InterruptedException e) {
						// TODO Auto-generated catch block
						e.printStackTrace();
					}
	     			//Test.parseLog(log);
			}
		}
	}
	
	//parseLog方法内部的代码不能改动
	public static void parseLog(String log){
		System.out.println(log+":"+(System.currentTimeMillis()/1000));
		
		try {
			Thread.sleep(1000);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}		
	}
	
}

第二题参考答案

public class Test {

	public static void main(String[] args) {
		final Semaphore semaphore = new Semaphore(1);
		final SynchronousQueue<String> queue = new SynchronousQueue<String>();
		for(int i=0;i<10;i++){
			new Thread(new Runnable(){
				@Override
				public void run() {	
					try {
						semaphore.acquire();
						String input = queue.take();
						String output = TestDo.doSome(input);
						System.out.println(Thread.currentThread().getName()+ ":" + output);
						semaphore.release();
					} catch (InterruptedException e) {
						// TODO Auto-generated catch block
						e.printStackTrace();
					}	
				}
			}).start();
		}
		
		System.out.println("begin:"+(System.currentTimeMillis()/1000));
		for(int i=0;i<10;i++){  //这行不能改动
			String input = i+"";  //这行不能改动
			try {
				queue.put(input);
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}
}

//不能改动此TestDo类
class TestDo {
	public static String doSome(String input){
		
		try {
			Thread.sleep(1000);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		String output = input + ":"+ (System.currentTimeMillis() / 1000);
		return output;
	}
}

第三题参考答案

package syn;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.concurrent.CopyOnWriteArrayList;

//不能改动此Test类	
public class Test extends Thread{
	
	private TestDo testDo;
	private String key;
	private String value;
	
	public Test(String key,String key2,String value){
		this.testDo = TestDo.getInstance();
		/*常量"1"和"1"是同一个对象，下面这行代码就是要用"1"+""的方式产生新的对象，
		以实现内容没有改变，仍然相等（都还为"1"），但对象却不再是同一个的效果*/
		this.key = key+key2; 
/*		a = "1"+"";
		b = "1"+""
*/
		this.value = value;
	}


	public static void main(String[] args) throws InterruptedException{
		Test a = new Test("1","","1");
		Test b = new Test("1","","2");
		Test c = new Test("3","","3");
		Test d = new Test("4","","4");
		System.out.println("begin:"+(System.currentTimeMillis()/1000));
		a.start();
		b.start();
		c.start();
		d.start();

	}
	
	public void run(){
		testDo.doSome(key, value);
	}
}

class TestDo {

	private TestDo() {}
	private static TestDo _instance = new TestDo();	
	public static TestDo getInstance() {
		return _instance;
	}

	//private ArrayList keys = new ArrayList();
	@SuppressWarnings("rawtypes")
	private CopyOnWriteArrayList keys = new CopyOnWriteArrayList();
	public void doSome(Object key, String value) {
		Object o = key;
		if(!keys.contains(o)){
			keys.add(o);
		}else{
			for(Iterator iter=keys.iterator();iter.hasNext();){
				try {
					Thread.sleep(20);
				} catch (InterruptedException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
				Object oo = iter.next();
				if(oo.equals(o)){
					o = oo;
					break;
				}
			}
		}
		synchronized(o)
		// 以大括号内的是需要局部同步的代码，不能改动!
		{
			try {
				Thread.sleep(1000);
				System.out.println(key+":"+value + ":"
						+ (System.currentTimeMillis() / 1000));
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}

}