Question

Error in java when creating Threads. The error is in “MainApp” with RandomCharacterThread being the error. The Thread t1 is expecting a char whereas i am giving it an int value. This is what had caused the error. I have added comments to make the code clearer for the community.

//Main class.
//program to display random numbers and characters using threads.
public class MainApp 
{

    public static void main(String[] args)
    {
        new MainApp().start();
    }
    public void start()
    {
        Thread t1 = new Thread (new RandomCharacterThread("1"));
        t1.start();

    }

}


//RandomCharacterThread.
//Imports.
import java.util.Random;
//=====================================================================
public class RandomCharacterThread implements Runnable
{
//Variables.
    char letter;
    int repeats;
    Random rand = new Random();
//Constructor
//=====================================================================
public void RandomCharacterThread(char x)
{
    letter = x;
    repeats = rand.nextInt(999);
}
public void run()
{
    try
    {
        for(int i = 0;i < repeats; i++)
        {
            System.out.println("Character: " + letter);
        }

    }
    catch(Exception e)
    {

    }
}

}

Answer 1

Your “constructor” takes a char as an argument; you’re passing a String. You’d want to do something like

    Thread t1 = new Thread (new RandomCharacterThread('1'));

Note the single quotes rather than double quotes, which makes this a char constant rather than a String with one character.

I say “constructor” in quotes because you actually don’t have one: you have a method that returns void with the same name as the class. Remove the “void” and you’ll be good. Constructors have no return type at all:

public RandomCharacterThread(char x) 
{
    ...

This is a very common newbie mistake, but most people only make it once!