How do I fix the 'threads cannot be resolved to a variable' error?

Question

public class UnsynchronizedCounterTest{






/**
 * A class representing a counter with a method for incrementing the coutner. No synchronization is used
 * so this counter is not thread safe
 * @author
 *
 */
static class Counter{
    int count;
    void inc() {
        count = count+1;
    }
    int getCount() {
        return count;
    }
}
static Counter counter; // The counter that will be incremented. Since it is a global static variable, it is used by all threads of type HWUExercise12_1Thread. It is shared resource
static int numberOfIncrements; 

static class IncrementerThread extends Thread{
    public void run() {
        for (int i=0; i < numberOfIncrements; i++) {
            counter.inc();
        }   
    }
}

/**
 * The main program runs in a loop until the user want to exit. Each time through the loop, it runs one experiemtn.
 * It gets the number of threads and the number of increments per thread from the user. It creates and starts the 
 * threads, and then waits for all to finsih. It prints the fibna lvalue of the counter, as well as the expected value. 
 * The program ends when the user enters a number less than or equal to zero as the number of threads.
 * @param Args
 */


public static void main(String Args[]){
    Counter counter = new Counter();

    Scanner reader = new Scanner(System.in);

    while(true) {

    System.out.print("Enter the number of threads");
    int numberOfThreads = Integer.parseInt(reader.nextLine());





    if (numberOfThreads < 0) {
        break;

    }do {
        System.out.print("Enter the number of increments per thread");
        int numberOfIncrements = reader.nextInt();

    //create thread array
    IncrementerThread [] threads = new IncrementerThread[numberOfThreads];

    //Create a thread for each position in array
    for (int i=0; i< threads.length; i++) {
        threads[i] = new IncrementerThread();
    }
    }while (numberOfIncrements <= 0);



    //start the threads
    for (int i=0; i < numberOfThreads; i++) {
        threads[i].start();
    }
    try {   
    for(int j=0; j< numberOfThreads; j++) {
        threads[j].join();
    }
    System.out.println("The finanl value of the counter is" + counter.getCount());
    }catch(InterruptedException e) {
        e.printStackTrace();
    }
    }


}
}

For this program, I created a thread class (not thread-safe) that calls the inc () method in the nested class, a specified number of times. My program is supposed to create several threads and start them all and then wait for all the threads to terminate. I also have to print the final value of the counter. My error is that the eclipse is saying the the thread array I created, threads cannot be resolved to a variable. It's giving me an error for the lines

threads[i].start();

threads[j].join();

I'm a beginner in java and I'm not sure how to fix this issue. My question is that why is it saying threads cannot be resolved to a variable when I clearly have a thread object array? Thanks.

Answer 1

这是一个有效的代码：

public class UnsynchronizedCounterTest{

static Counter counter;

public static void main(String Args[]){
    new UnsynchronizedCounterTest().startCounting();
}

public void startCounting() {
    counter = new Counter();

    Scanner reader = new Scanner(System.in);

    while(true) {

        System.out.print("Enter the number of threads: ");
        int numberOfThreads = reader.nextInt();

        if (numberOfThreads <= 0) {
            break;
        }

        IncrementerThread [] threads;

        do {
            System.out.print("Enter the number of increments per thread");
            numberOfIncrements = reader.nextInt();

        //create thread array
            threads = new IncrementerThread[numberOfThreads];

            //Create a thread for each position in array
            for (int i=0; i< threads.length; i++) {
                threads[i] = new IncrementerThread();
            }
        }while (numberOfIncrements <= 0);



        //start the threads
        for (int i=0; i < numberOfThreads; i++) {
            threads[i].start();
        }
        try {   
            for(int j=0; j< numberOfThreads; j++) {
                threads[j].join();
            }
            System.out.println("The finanl value of the counter is: " + counter.getCount());
        } catch(InterruptedException e) {
            e.printStackTrace();
        }
    }
}

class IncrementerThread extends Thread{
    @Override
    public void run() {
        for (int i=0; i < numberOfIncrements; i++) {
            counter.inc();
        }   
    }
}

class Counter{
    int count = 0;
    void inc() {
        count = count+1;
    }

    int getCount() {
        return count;
    }
}

}