Question

Hello I am writing this program, and I am trying to figure out how to compare two items in an array to find the largest item.

public static <T extends Comparable< ? super T>> T getLargest(T [] a, int low, int high){
    if(low>high)
            throw new IllegalArgumentException();
    T[] arrCopy = (T[]) new Object[high-low]
    for(int i=low;i<high;i++){
        if(a[i]>a[i+1])
            arrCopy[i]=a[i];
        else
            arrCopy[i]=a[i+1];
    }
    return arrCopy[0];
}

But then I don’t know how to test for it, I tried :

T[] a = {1,12,7,45,22,23,5};
    System.out.println("Array: [1,12,7,45,22,23,5] low=0 high, Largest?: " + rec.getLargest(a, 0, 6));

but I get an error message

The method getLargest(T[], int, int) in the type Rec is not applicable for the arguments (int[], int, int)

How do I call it to make it an array of numbers? Would an array of strings work with the code I have for getting the largest?

Maybe is just simple answers but I’ve been working on the whole program for a while and things don’t look so clear now.

EDIT

After changing the array from int[] to Integer[]. I am getting an error on this line if(a[i]>a[i+1])
saying

The operator > is undefined for the argument type(s) T, T

I’m assuming I would have to change the > sign to compare elements in the array, but how do I do this? Use compareTo() ?

Answer 1

It’s not working because int isn’t a subclass of Comparable because it’s not even an Object. Basically, you can’t use primitives (int, short, long, char, boolean, byte) with generics.

Try calling it with an array of Integer.

Integer[] a = {1,12,7,45,22,23,5};
System.out.println("Array: [1,12,7,45,22,23,5] low=0 high, Largest?: " + rec.getLargest(a, 0, 6))

If you want your method to be able to accept int[], you’ll need to have a separate function for each one you want to accept (int getLargest(int[], int, int), char getLargest(char[], int, int), etc.).

EDIT:

In response to your edit, you need to use compareTo(). < is only defined for primitives.