Random Generator semantic error

Question

I need to create a public class method for a class RandomGenerator called getRandomNumber() which takes a single int argument and returns a random number between 1 and its argument (inclusive) which is generated by sending a suitable nextInt() message to the class variable rand.
This is my code so far.
import java.util.Random;
import ou.*;
* Class RandomGenerator - write a description of the class here.
* @author (your name)
* @version (a version number or a date)
public class RandomGenerator
     /* instance variables */
     private int exampleVar; // replace this example variable with your own
      * Default constructor for objects of class RandomGenerator
     public RandomGenerator()
          super();
     private Random rand = new Random();
    public int getRandomNumber(int num)
        int ranum;
        String StringNum;
        StringNum = OUDialog.request("Please enter a number");
        num = Integer.parseInt(StringNum);
        if (num <=0)
        StringNum = OUDialog.request("Please enter a positive integer");
        return
        ranum = rand.nextInt(num);
        When I test it I get the error 'Semantic error: Cannot reach instance method: getRandomNumber( int ) from static context: RandomGenerator'
I don't understand what the error means.

Answer 1

When calling methods, you can either call the method on an object (an instance of a class), or directly on the class. Calling a method directly on the class assumes that the method is static, which means that the method is shared among all instances of the class, rather than each instance having it's own version.
For instance, this line in your code:
num = Integer.parseInt(StringNum);You called the parseInt() method of the Integer class statically, because parseInt() is a static method. You don't need a previous integer value to call parseInt(). Now the Integer class also has a method called intValue() which returns the current value of the Integer as an int. Obviously, if there's no int value stored in the integer, calling that method would be useless:
Integer.intValue(); //no value to return
Integer anInteger = new Integer(3);
int anInt = anInteger.intValue(); //returns 3So since your getRandomNumber() method is not static, you must have an instance of the RandomGenerator class to call it on, like the post above shows.