Binary Search with Primitive Types

Question

I am currently in a class for Java Programming and am completely new to Java. I am trying to create a program that will use binary search for the value 45.3

class findValue {
public static void main(String args[]) {
    double a[] = new double[6]; //declaration

    a[0] = -3; //initialization
    a[1] = 10;
    a[2] = 5;
    a[3] = 24;
    a[4] = 45.3;
    a[5] = 10.5;

    int n = a.length; //storing length of array
    int temp = 0; //declaring temporary storage place

    for (int i = 0; i < n; i++) {
        for (int j = 1; j < (n - i); j++) {

            if (a[j - 1] > a[j]) {
                temp = (int)a[j - 1];
                a[j - 1] = a[j];
                a[j] = temp; //bubble sorting
            };
        };
    };
    System.out.println("45.3 found" + binarySearch(a, 45.3));
};
public static void binarySearch(Integer[] a, int x) {
    int low = 0;
    int high = a.length - 1;
    int mid; //values for binary search

    while (low <= high) {
        mid = (low + high) / 2; //setting value for searching

        if (a[mid].compareTo(x) < 0) {
            low = mid + 1;
        }
        else if (a[mid].compareTo(x) > 0) {
            high = mid - 1;
        };
    };
};

This is the compiler error I got:

Line: 25
method binarySearch in class findValue cannot be applied to given types;
required: java.lang.Integer[],int
found: double[],double
reason: actual argument double[] cannot be converted to java.lang.Integer[] by method invocation conversion

Answer 1

(I know there is a lot of room for improvement, but I'm just suggesting the minimum number of changes for the program to work)

The method

public static void binarySearch(Integer[] a, int x) {...}

is expecting integers, but we want it to use doubles insted. This means that the arguments should be an array of doubles, and the double to find:

public static void binarySearch(double[] a, double x) {...}

This said, we know that this function will return an int, so we set the return type:

public static double binarySearch(double[] a, double x) {...}

Now, finally, we must return the number we were looking for by adding the following at the end of the method (after the while):

return mid;

The final result should be:

class findValue {
    public static void main(String args[]) {
        double a[] = new double[6]; //declaration

        a[0] = -3; //initialization
        a[1] = 10;
        a[2] = 5;
        a[3] = 24;
        a[4] = 45.3;
        a[5] = 10.5;

        int n = a.length; //storing length of array
        int temp = 0; //declaring temporary storage place

        for (int i = 0; i < n; i++) {
            for (int j = 1; j < (n - i); j++) {

                if (a[j - 1] > a[j]) {
                    temp = (int)a[j - 1];
                    a[j - 1] = a[j];
                    a[j] = temp; //bubble sorting
                }
            }
        }
        System.out.println("45.3 found: " + binarySearch(a, 45.3));
    }
    public static int binarySearch(double[] a, double x) {
        int low = 0;
        int high = a.length - 1;
        int mid = (low + high) / 2; //values for binary search

        while (low <= high) {
            mid = (low + high) / 2; //setting value for searching

            if (Double.compare(a[mid], (double)x) < 0) {
                low = mid + 1;
            }
            else if (Double.compare(a[mid], (double)x) > 0) {
                high = mid - 1;
            }
        }
        return mid;
    }
}

Output:

45.3 found: 5