为什么我的二进制搜索不返回目标值索引

Question

I'm working on a coding problem that wants me to use a binary search method to see if a value by the user matches the value in the array that I extracted from a file. My binary search however only recognizes the first number inside the array as the target.

I've been wracking my brain for a few hours now and I don't know what's wrong.

public static void main(String[] args) throws FileNotFoundException {
    final double THRESHOLD = 0.01; //set threshold for doubles comparison
    boolean done = false;
    File fileName;
    Scanner in = new Scanner (System.in);
    Scanner user;
    //prompt user to input a file
    while (!done) {
        System.out.print("Enter the name of the file with your investments: ");
        fileName = new File(in.nextLine());
        user = new Scanner (fileName);
        int size = user.nextInt();
        double investments [] = new double [size];
        int index = 0;
        while (user.hasNextDouble()) {
            investments [index] = user.nextDouble(); 
            index++;
        }
        //sort values into specified categories
        int i = 0, aValues = 0, bValues = 0, cValues = 0, dValues = 0, fValues = 0;
        while (i < investments.length) {
            if (investments [i] > 1250) {
                aValues++;
            }
            if (investments [i] > 1100 && investments [i] < 1500) {
                bValues++;
            }
            if (investments [i] > 900 && investments [i] < 1100) {
                cValues++;
            }
            if (investments [i] > 750 && investments [i] < 900) {
                dValues++;
            }
            if (investments [i] > 0 && investments [i] < 750) {
                fValues++;
            }
        i++;
        }
        //print table
        System.out.printf("\n%-10s$%.2f", "Mean: ", getMean(investments));
        System.out.printf("\n%-10s$%.2f", "Minimum", getMinimum(investments));
        System.out.printf("\n%-10s$%.2f\n", "Maximum", getMaximum(investments));
        System.out.printf("\n%-10s", "Number of As: " + aValues);
        System.out.printf("\n%-10s", "Number of Bs: " + bValues);
        System.out.printf("\n%-10s", "Number of Cs: " + cValues);
        System.out.printf("\n%-10s", "Number of Ds: " + dValues);
        System.out.printf("\n%-10s\n", "Number of Fs: " + fValues);
        System.out.printf("\n%-10s", "Total number of investments: " + size);
        System.out.printf("\n\n");
        //sort array of investments and print
        bubbleSort (investments);
        for (double nvestments : investments) {
            System.out.printf("%.3f\n", nvestments);
        }
        System.out.print("Would you like to search for an investment amount? (Y/N): ");
        String response = in.next();
        do {
        if (response.equalsIgnoreCase("y")) {

            System.out.print("Enter investment amount: $");
            double enteredTarget =  in.nextDouble();
            if (THRESHOLD >= Math.abs(investments[binarySearch(investments, enteredTarget)] - enteredTarget)) {
                done = false;
                System.out.println(investments[binarySearch(investments, enteredTarget)] + "       " + enteredTarget);
                System.out.printf("Investment amount $%.2f is found at position %d\n", enteredTarget, index(investments, enteredTarget)+1);
                System.out.print("Would you like to search for an investment amount? (Y/N): ");
                response = in.next();
            }
            else {
                System.out.println(investments[binarySearch(investments, enteredTarget)] + "       " + enteredTarget);
                System.out.printf("Investment amount $%.2f is found at position 00\n", enteredTarget);
                System.out.print("Would you like to search for an investment amount? (Y/N): ");
                response = in.next();
            }}
            else if (response.equalsIgnoreCase("n")) {
                done = true;
            }
        } while (response.equalsIgnoreCase("y"));
    }
in.close();
}
public static double getMinimum (double [] array) {
    double minValue = array [0];
    for (int i=1; i<array.length; i++) {
        if (array [i] < minValue) {
            minValue = array[i];
        }
    }
    return minValue;
}
public static double getMaximum (double [] array) {
    double maxValue = array [0];
    for (int i=1; i<array.length; i++) {
        if (array [i] > maxValue) {
            maxValue = array[i];
        }
    }
    return maxValue;
}
public static double getMean (double [] array) {
    double sum = 0;
    for (int i = 0; i < array.length; i++) {
        sum = array [i] + sum;
    }
    double mean = sum / array.length;
    return mean;
}
public static void bubbleSort (double [] array) {
    boolean sorted = false;
    int i = 0, j = 0;
    while (!sorted) {
        if (i == array.length) {
            sorted = false;
        }
        else {
            sorted = true;
            for (i = 0; i < array.length-1; i++) {
                for (j = 0; j < array.length-i-1; j++) {
                    if (array [j] < array [j+1]) {
                        swap (array, j, j+1);
                    }
                }
            }
        }
    }
}
public static void swap (double [] array, int j, int i) {
    double temp = array [i];
    array [i] = array [j];
    array [j] = temp;
}
public static int binarySearch (double [] array, double target) {
    int lb = 0;
    int ub = array.length - 1;
    int retVal = -1;
    while (ub >= lb && retVal < 0) {
        int mid = (ub + lb) / 2;
        if (array [mid] < target) {
            lb = mid + 1;
        }
        else if (array [mid] > target) {
            ub = mid - 1;
        }
        else {
            retVal = mid;
        }
    }
return retVal;
}
public static int index (double [] array, double target) {
    int i;
    final double THRESHOLD = 0.01;
    for (i = 0; i < array.length; i++) {
        if (Math.abs(array [i] - target) < THRESHOLD) {
            return i;
        }
    }
return i+1;
}

}

For instance, if my array contains 800.9, 300, 100, 60.50, 23.45, & 23.33 and I type 100 when it asks me to enter a value, it compares it to 800.9 and not the rest of the values.

Answer 1

Binary Search only works on Sorted Arrays and in your case your array is sorted in Descending order and you implement a Binary Search algorithem for Ascending order .

Your Array : 800.9, 300, 100, 60.50, 23.45, & 23.33 // Descending order

For Descending order Array you have to inverse your conditional operators.

if (array [mid] > target) {
    lb = mid + 1;
}
else if (array [mid] < target) {
    ub = mid - 1;
}
else {
    retVal = mid;
}