javaLogic errorMedium

Array clone produces shallow copy of 2D matrix

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BugFind the bug and fix the code

What it should do

Clone 2D array and mutate first cell without modifying original. Example: cloneAndMutateMatrix(99) -> [0, 99]

What happens instead

Original matrix row is mutated because array.clone() only copies row references

public class Main {
    public static int[] cloneAndMutateMatrix(int newVal) {
        int[][] original = {{0, 1}, {2, 3}};
        // .clone() on 2D array copies array of pointers to the inner rows!
        int[][] clone = original.clone();
        clone[0][0] = newVal;
        return new int[]{original[0][0], clone[0][0]};
    }

    public static void main(String[] args) {
        int[] res = cloneAndMutateMatrix(99);
        System.out.println(res[0] + ", " + res[1]);
    }
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

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This bug belongs to the logic errors pattern

The wrong operator, an inverted condition, a formula the right way round but backwards.

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public class Main { public static int[] cloneAndMutateMatrix(int newVal) { int[][] original = {{0, 1}, {2, 3}}; // .clone() on 2D array copies array of pointers to the inner rows! int[][] clone = original.clone(); clone[0][0] = newVal; return new int[]{original[0][0], clone[0][0]}; } public static void main(String[] args) { int[] res = cloneAndMutateMatrix(99); System.out.println(res[0] + ", " + res[1]); } }

Array clone produces shallow copy of 2D matrix

What it should do

What happens instead

More logic errors to practise

Array clone produces shallow copy of 2D matrix

What it should do

What happens instead

More logic errors to practise