迅雷笔试的一道多线程题目解答
/**************************************************************** * 迅雷笔试题： * 有三个线程ID分别是A、B、C,请有多线编程实现，在屏幕上循环打印10次ABCABC… * * @author: heartraid *****************************************************************//** * 锁码：公共数据区 * 码值：码值为A，表示应该由A线程来执行，B,C线程等待 * 码值为B,C同理。 */class LockCode{ /**当前锁码码值，初始码值为A，表示最初由A线程运行*/ private char code='A'; /**单例模式*/ private LockCode(){ } public static LockCode newInstance(){ return new LockCode(); } /** * 循环设置锁码 * 每一次调用，锁码按照A-B-C-A-...-的顺序循环往复 */ public void setCode(){ this.code=(char)(this.code+1); if(this.code=='D') this.code='A'; } /** * 得到锁码 */ public char getCode(){ return this.code; }}/** * 完成打印工作的线程类 */class PrintRunnable implements Runnable{ /**需要打印的字符*/ private char character='?'; /**公共锁码*/ private LockCode lockCode=null; PrintRunnable(char c,LockCode l){ this.character=c; this.lockCode=l; } /** * 线程执行 */ public void run() { int loopCount=1; while(loopCount<=10){ synchronized(lockCode){//线程同步操作锁码 try{ //如果当前运行的线程并不等于当前锁码的码值，则改线程等待 //比如当前运行线程是A，但是码值为B，则A线程等待。 while(lockCode.getCode()!=this.character) lockCode.wait(); //码值匹配成功，打印字符 System.out.print(this.character); //循环10次记数 loopCount++; //设置码值，让下一个线程可以运行 lockCode.setCode(); //让其他所有等待线程激活 lockCode.notifyAll(); }catch(InterruptedException e){ e.printStackTrace(); } } } } }/** * 测试 */public class ThreadLoopPrint { public static void main(String[] args) { LockCode lockCode=LockCode.newInstance();//公共锁码 Thread ta=new Thread(new PrintRunnable('A',lockCode)); Thread tb=new Thread(new PrintRunnable('B',lockCode)); Thread tc=new Thread(new PrintRunnable('C',lockCode)); ta.start(); tb.start(); tc.start(); }}package self.saturday.part13;public class Tencent { public static void main(String[] args){ Signal s=new Signal(3); StringPrinter p1=new StringPrinter("A",s), p2=new StringPrinter("B",s), p3=new StringPrinter("C",s); p1.start(); p2.start(); p3.start(); }}class StringPrinter extends Thread{ static int threadCount=0; private Signal signal; private String printStr; private int order; public StringPrinter(String str,Signal s){ signal=s; printStr=str; order=threadCount++; } public void run(){ int loopCount=0; while(loopCount<10){ synchronized(signal){ //等待信号量 while(signal.getValue()!=order){ try { signal.wait(); } catch (InterruptedException e) { throw new RuntimeException(e); } } //执行操作 System.out.print(printStr); signal.next(); loopCount++; //唤醒其他线程 signal.notifyAll(); } } }}class Signal{ private int value=0; private int signalCount; public Signal(int count){ signalCount=count; } public int getValue(){ return value; } public void next(){ value++; if(value==signalCount){ value=0; } }}
[解决办法]
我也大致写了一个
static class PrintThread extends Thread{ private static class Entry{ String id; Entry next; Entry previous; Entry(String id){ this.id = id; } } private static Entry header; private static int MaxPrintCount = 10; private Entry myLock; public PrintThread(String id){ myLock=new Entry(id); addEntry(myLock); } private void addEntry(Entry e) { if(header==null){ header=e; header.next=header.previous=e; }else{ header.previous.next=e; e.previous=header.previous; header.previous=e; e.next=header; } } public void run(){ try{ for(int i=0;i<MaxPrintCount;i++){ if(!(i==0 && myLock==header)){//第一个线程首次打印不阻塞。 synchronized (myLock) { myLock.wait(); } } printId(); synchronized (myLock.next) { myLock.next.notify(); } } }catch(InterruptedException e){ e.printStackTrace(); } } private void printId() { System.out.print(myLock.id); } } public static void main(String[] args) { PrintThread pta = new PrintThread("A"); PrintThread ptb = new PrintThread("B"); PrintThread ptc = new PrintThread("C"); PrintThread ptd = new PrintThread("D"); //线程启动要倒序。 ptd.start(); ptc.start(); ptb.start(); pta.start(); }
[解决办法]
import java.util.HashMap;import java.util.Map;public class Xunlei { private Object lock=new Object(); private static Map<String,Boolean> map=new HashMap<String,Boolean>(); static { map.put("A",true); map.put("B",false); map.put("C",false); } public static void main(String[] args) { Xunlei xl=new Xunlei(); xl.new taskThread("A").start(); xl.new taskThread("B").start(); xl.new taskThread("C").start(); } public class taskThread extends Thread { public taskThread(String name) { super.setName(name); } public void run() { while(true) { synchronized(lock) { if(this.getName().equals("A")) { if(map.get("A")) { setOpen("B"); System.out.println("A"); } }else if(this.getName().equals("B")) { if(map.get("B")) { setOpen("C"); System.out.println("B"); } }else if(this.getName().equals("C")) { if(map.get("C")) { setOpen("A"); System.out.println("C"); } } } try { Thread.sleep(3000); } catch (InterruptedException e) { e.printStackTrace(); } } } } public void setOpen(String key) { for(Map.Entry<String, Boolean> m:map.entrySet()) { map.put(m.getKey(), false); } map.put(key, true); }}