一道关于笔试的多线程题目

四个线程t1,t2,t3,t4,向4个文件中写入数据，t1只能写入1，t2只能写入2，t3只能写入3，t4只能写入4，对4个文件A，B，C，D写入如下内容: A:123412341234..... B:234123412341.... C:341234123412.... D:412341234123.... 怎么实现同步可以让线程并行工作？ import java.io.FileWriter; import java.io.PrintWriter; import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.ReentrantLock;public class Hello {static boolean b=false;static ReentrantLock lock=new ReentrantLock(); static ReentrantLock lock_2=new ReentrantLock();static Condition condition_for=lock.newCondition();//线程Thread_t1~Thread_t4分别只写入1~4class Thread_t1 extends Thread{String path;Thread_t1(String path){this.path=path;}public void run(){print(path,1);}}class Thread_t2 extends Thread{String path;Thread_t2(String path){this.path=path;}public void run(){print(path,2);}}class Thread_t3 extends Thread{String path;Thread_t3(String path){this.path=path;}public void run(){print(path,3);}}class Thread_t4 extends Thread{String path;Thread_t4(String path){this.path=path;}public void run(){print(path,4);}}//写入方法public void print(String path, int i){lock_2.lock();PrintWriter pw=null;try {pw=new PrintWriter(new FileWriter("c:/work/abcd/"+path+".txt",true),true);pw.print(i);} catch (Exception e) {e.printStackTrace();}finally{pw.close();lock_2.unlock();}}//文件类A~Dclass File_A implements Runnable{int one,two,three,four;File_A(int one,int two, int three, int four){this.one=one;this.two=two;this.three=three;this.four=four;}public void run(){for(int x=0;x<100;x++){select("A",one,two,three,four);}}}class File_B implements Runnable{int one,two,three,four;File_B(int one,int two, int three, int four){this.one=one;this.two=two;this.three=three;this.four=four;}public void run(){for(int x=0;x<100;x++){select("B",one,two,three,four);}}}class File_C implements Runnable{int one,two,three,four;File_C(int one,int two, int three, int four){this.one=one;this.two=two;this.three=three;this.four=four;}public void run(){for(int x=0;x<100;x++){select("C",one,two,three,four);}}}class File_D implements Runnable{int one,two,three,four;File_D(int one,int two, int three, int four){this.one=one;this.two=two;this.three=three;this.four=four;}public void run(){for(int x=0;x<100;x++){select("D",one,two,three,four);}}} //选择线程方法，当前只允许进入一个文件线程public void select(String path,int one,int two, int three, int four){lock.lock();try{while(b){condition_for.await();}b=true;int[] order={one,two,three,four};//将传入的1234，换成数组方便用for遍历for(int i:order){switch(i){case 1:Thread_t1 t1= new Thread_t1(path);t1.start();t1.join(); //t1.join()是等线程t1执行完后再执行当前线程break;case 2:Thread_t2 t2= new Thread_t2(path);t2.start();t2.join();break;case 3:Thread_t3 t3= new Thread_t3(path);t3.start();t3.join();break;case 4:Thread_t4 t4= new Thread_t4(path);t4.start();t4.join();break;} }b=false;}catch(Exception e){e.printStackTrace();}finally{lock.unlock();}}//主函数public static void main(String args[]){HelloJava hj=new HelloJava();new Thread(hj.new File_A(1,2,3,4)).start();new Thread(hj.new File_B(2,3,4,1)).start();new Thread(hj.new File_C(3,4,1,2)).start();new Thread(hj.new File_D(4,1,2,3)).start();} }

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