How can I change the values exceeding the int data type to the long data type in this code?

Question

In the last portion of this code (where the last for loop and if statements are), I'm trying to change the data type of the integers to long when they exceed the integer data type limit. What am I doing wrong in this code? When I run, I get the same values as before I even tried to change them to long (which are increasingly huge integers until they get negative).

public class UniqueElements {
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        int maxValue = 0;
        int numElements = 0;
        int programRuns = 12;
        Scanner sc = new Scanner(System.in);
        for (int newExecution = 0; newExecution <= programRuns; newExecution++ ) {
            System.out.print("Enter the maximum value for an element: ");
            //prompt user to enter the maximum value
            maxValue = sc.nextInt(); //user input for max value
            System.out.print("Enter the number of elements in the array: ");
            numElements = sc.nextInt(); //number of elements in an array
            int A[] = new int[numElements];
            //array comprising of the number of elements chosen by the user
            int totalComp = 0; //set total comparisons to 0
            for (int runs = 1; runs <= 100; runs++) { //program runs 100 times
                Random rand = new Random(System.nanoTime());
                //initiate the random number generator
                int numComp = 0; //set number of comparisons to 0
                for (int index = 0; index < numElements; index++) { 
                    A[index] = rand.nextInt(maxValue); 
                    //length of array is the number of elements the user puts in
                }
                for (int i = 0; i < A.length; i++) { //for each integer in the array
                    for (int j = i + 1; j < A.length; j++) { 
                        //for each integer following i
                        if (A[i] == A[j]) { //if the are equal to eachother
                            //end the if statement
                            break;
                        }
                        if (numComp == (int)numComp) {
                           numComp++; 
                        }
                        else {
                            Long.valueOf(numComp);
                            numComp++;
                        }
                    }
                }
                totalComp+= numComp; 
            } //end 100 loops
            if (totalComp == (int)totalComp) 
                System.out.println("Average number of comparisons: " + totalComp / 100);
            else {
                System.out.println("Average number of comparisons: " + 
                                    Long.valueOf(totalComp) / 100L);
            }

            }
        }
    }

score 0 · Answer 1 · answered Sep 29 '16 at 04:21

0

update:

somehow.... changing the total number of runs to 2 and dividing the totalComp variable by 2 and 2L made it work. Anyone know how that changed it?

answered Sep 29 '16 at 04:21

Nicholas Whitfield

45
5

score 0 · Answer 2 · edited May 23 '17 at 12:15

You can't change the type of a variable after it's already been declared. You can cast that variable to another type, or "interpret" it as another type (as in your Long.valueOf()), but the variable still remains whatever type you declared it as.

In your code, you've declared totalComp to be an int, which in Java means it holds 32 bits (one of which is a sign bit). There's no way to make Java store more than 32 bits in an int. If you continue to add beyond Integer.MAX_VALUE, or subtract below Integer.MIN_VALUE, the value in the variable will simply under/overflow. So this statement after your for loop isn't doing what you expect, and will always be true: if (totalComp == (int)totalComp)

In other words, you can't go "back in time" and re-declare your primitive int as a long because you found out at runtime that you need to store larger values. The easiest way to solve this problem would be to declare totalComp as a long. If for some reason you can't change the type of totalComp, it is possible to detect overflow/underflow before performing the calculation; see this answer for details.

How can I change the values exceeding the int data type to the long data type in this code?

2 Answers2