使用方法的冒泡排序数组

Question

I'm writing code that takes the input for the array length and the items on the array, it then uses a bubble sorting method to put the items of the array in order.

This is the desired input output

Enter the number of items in array:
5

Enter the items:
5
6
4
2
3

The sorted array is:
2
3
4
5
6

The problem I'm having is the method does not seem to be reading the user's inputs.

This is the code I have

import java.util.Scanner;

public class Main {
    private static int[] array;
    public static void main(String[] args) {
        int arrayLength;
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter the number of items in array: ");
        arrayLength = scanner.nextInt();
        int[] array = new int[10];
        System.out.println("Enter the items: ");
        for (int i = 0; i < arrayLength; i++) {
            array[i] = scanner.nextInt();
        }
        bubbleSort();
    }

    public static void bubbleSort() {
        int i, j, temp;
        boolean swap;
        for (i = 0; i < array.length - 1; i++) {
            swap = false;
            for (j = 0; j < array.length - i - 1; j++) {
                if (array[j] > array[j + 1]) {
                    temp = array[j];
                    array[j] = array[j + 1];
                    array[j + 1] = temp;
                    swap = true;
                }
            }
            if (swap == false)
                break;
        }
        System.out.print("The sorted array is: ");
        for (i = 0; i < array.length; i++) {
            System.out.print(array[i] + " ");
            System.out.println();
        }
    }
}

Answer 1

Break the problem down into smaller problems. Each of these small problems will become a method. A method has inputs (arguments) and an output (a return value). One way to look at what you're trying to do is:

1. Read in an array
2. Sort the array
3. Print the sorted array

The first method will return an int[] given an InputStream :

static int[] readArray(InputStream in) {
    System.out.print("Enter the number of items in array: ");
    Scanner scanner = new Scanner(in);
    int arrayLength = scanner.nextInt();
    int[] array = new int[arrayLength]; // there was a problem here, in your code the array had a fixed length of 10

    System.out.println("Enter the items: ");
    for (int i = 0; i < arrayLength; i++) {
        array[i] = scanner.nextInt();
    }
    return array;
}

The second method will return an int[] sorted with the bubble sort algorithm, given an int[] argument.

static int[] bubbleSort(int[] array) {
    int i, j, temp;
    boolean swap;
    for (i = 0; i < array.length - 1; i++) {
        swap = false;
        for (j = 0; j < array.length - i - 1; j++) {
            if (array[j] > array[j + 1]) {
                temp = array[j];
                array[j] = array[j + 1];
                array[j + 1] = temp;
                swap = true;
            }
        }
        if (!swap) {
            break;
        }
    }
    return array;
}

The third will print it out, returning nothing ( void ).

static void print(int[] array) {
    for (int i = 0; i < array.length; i++){
        System.out.println(array[i]);
    }
}

Put the pieces together and you have

public static void main(String[] args) {
    // get input from user
    int[] array = readArray(System.in);
    // sort it
    int[] sorted = bubbleSort(array);
    // print sorted array
    System.out.println("The sorted array is: ");
    print(sorted);
}

As noted in the comment in the readArray(InputStream) method, there was a problem in your original code since the array's length was fixed (10). These kinds of problems are easier to spot when using concise methods that do just one thing. By breaking the code down into smaller pieces it's also easier to test it.

Answer 2

1. Please be consistent with your use of spaces around names and symbols. It will make your code look as though it was written by someone who cares, rather than someone who just head-butted the keyboard strategically. This will instinctively make people think better of you and your work, always a good thing to aim for:)

2. int[] array = new int[10]; is problematic. Where did that 10 come from? Never, ever use magic numbers in your code. Even something like 12, to represent the number of months in a year, is technically a variable which could change one day. Assign the number to a named variable, and use the name instead. I would have hinted that here lies the source of your dilemma, but saka1029 got there first.

3. You declare a variable called array at the start of your class, but then define a duplicate in the main() method. User inputs are being added to the array in main(), but bubbleSort() is using the class variable which never gets anything added to it. Option 1: declare the array as a class variable and use it in each method. Option 2: declare it in main(), then pass it as a parameter when you invoke the sorting method, ie bubbleSort(array) . I would prefer the latter, as you are being much clearer about what bubbleSort is sorting.

4. Your methods do too much, and have different levels of abstraction, which is a pretty common feature for new programmers so don't feel bad about it. However, do improve it, main() has both fiddly details to get the information. and a method call in which the work to sort the array is handled elsewhere. That's an ugly and confusing mix, Abstract the data collection, just as you already did for the sorting. to make things more balanced, Ideally. your main() should read like an index of activities which are all handled in other methods, As for methods doing too much, your bubbleSort() sorts an array (good). but also and very unexpected prints it (bad). The method name does not indicate that the array gets printed. Let's try

public static void main(String[] args) {
    int[] array = getArray();
    bubbleSort(array);
    printArray(array);
}

Fix the errors which have crept in through points 2 and 3. Then, you don't have to change the logic of your code, just break it up into more logical methods:) Once you start routinely testing your code, this will be an incredibly important approach.