Question

I have to pass two strings to a thread, which will return an array containing both of them, and I must use callable.

Here’s what I have so far:

public class toArray implements Callable<String[]> {

private String string1 string2;

public toArray (String first, String second)
{
    string1= first;
    string2 = second;
}

    @Override
    public String[] call() throws Exception {
        String [] allStrings = null;
            allStrings[0] = string1;
            allStrings[1] = string2;
        return allStrings;
    }
}

Below is the main:

public class theFuntion{

    public static void main(String[] args) {


        FutureTask<String[]> task = new FutureTask (new MyCallable());
        ExecutorService es = Executors.newSingleThreadExecutor();
        es.submit (task);
        try{
               String[] result = task.get();
               System.out.println(result[1] + result[2]);
           }
        catch(Exception e){
                           System.err.println(e);
    }
         es.shutdown();
}

The problem is in main: it says that result is expecting a String[] but it’s getting an object. If I cast result it will say an exception must be declared to be thrown.

Answer 1

Change the signature of the class to

public class toArray implements Callable<String[]>

and the signature of the call method to

public String[] call() throws Exception

UPDATE:
Ok, there are more than one error…
See the following working sample

public class Test{

    public static void main(String[] args) {


        FutureTask<String[]> task = new FutureTask(new MyCallable("a", "b"));
        ExecutorService es = Executors.newSingleThreadExecutor();
        es.submit (task);
        try{
            String[] result = task.get();
            System.out.println(result[0] + result[1]);
        }
        catch(Exception e){
            System.err.println(e);
        }
        es.shutdown();
    }

    public static class MyCallable implements Callable<String[]>
    {

        private String string1, string2;

        public MyCallable (String first, String second)
        {
            string1= first;
            string2 = second;
        }

        @Override
        public String[] call() throws Exception {
            String [] allStrings = new String[2];
            allStrings[0] = string1;
            allStrings[1] = string2;
            return allStrings;
        }
    }
}