CODEWITHSUNDEEP
java
codingamateur
codingamateur

Reputation: 1

Issue trying to create a Bubble Sort using ArrayList<Integer>

Hi I'm trying to figure out how to use BubbleSort in Java and my code is erroring and I don't know why

import java.util.ArrayList;

public class SortsRunner {

    public static void BubbleSort(ArrayList<Integer> nums) {
        ArrayList<Integer> arr = new ArrayList<Integer>();
        int n = arr.size();
        for (int i = 0; i < n-1; i++) 
            for (int j = 0; j < n-i-1; j++) 
                if (arr.get(j) > arr.get(j+1)) 
                { 

                    int temp = arr.get(j); 
                    arr.get(j) = arr.get(j+1); 
                    arr.get(j+1) = temp; 
                }
        }
    public static void SelectionSort(ArrayList<Integer> nums) {

        }
    public static void printArrayList(ArrayList<Integer> nums) {
        for(int i = 0; i < nums.size(); i++) {
            System.out.println(nums.get(i) + " ");
            }
        System.out.println();
        }
    public static ArrayList<Integer> makeRandomArrayList() {
        ArrayList<Integer> nums = new ArrayList<>();
        for(int i = 0; i < (int)(Math.random() * 11) + 5; i++) {
            nums.add((int)(Math.random() * 100));
            }
        return nums;
        }

public static void main(String[] args) {
printArrayList(makeRandomArrayList());

}

}

When I get to arr.get(j) = arr.get(j+1); and arr.get(j+1) = temp; the left side errors saying "The left-hand side of an assignment must be a variable." can anyone help me fix this?

Upvotes: 0

Views: 114

Answers (2)

WJS
WJS

Reputation: 40034

You are doing several things wrong.

  1. The obivous get and set issues already mentioned.
  2. The fact that your are sorting an empty list. You pass in nums but sort the one you create which is empty.
  3. You should use a boolean to prevent unnecessary repeats of the outer loop. Think of it like this, if you don't make a swap on the first iteration of the outer loop, then you won't swap on subsequent iterations.

And one style suggestion. Don't use loops or if statements without {}. Even if they only contain a single line of code. You will be less likely to make coding errors if you do so.

Try the following:

    public static void BubbleSort(List<Integer> nums) {
        int n = nums.size();
        for (int i = 0; i < n; i++) {
            boolean swapped = false;
            for (int j = 0; j < n-1; j++) {
                if (nums.get(j) > nums.get(j + 1)) {
                    int temp = nums.get(j);
                    nums.set(j, nums.get(j + 1));
                    nums.set(j + 1, temp);
                    swapped = true;
                }
            }
            if (!swapped) {
                break;
            }
        }
    }

Upvotes: 0

Andy Turner
Andy Turner

Reputation: 140318

arr.get(j) = arr.get(j+1);
arr.get(j+1) = temp;

You're trying to assign a value to the result of a method call.

You just can't do this. You can only assign to a local variable, a field in the current class, a field access (e.g. foo.bar = ...) or an array element (e.g. foo[0] = ...).

Instead, you should use set to update a list element:

arr.set(j, arr.get(j+1));
arr.set(j+1, temp);

For the specific case of swapping two elements around in a list, you can instead use Collections.swap:

Collections.swap(arr, j, j+1);

Upvotes: 2

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