How Do You Efficiently Duplicate a 2D Array in Java?

Duplicating a Two-Dimensional Array in Java

When manipulating multidimensional arrays in Java, the need to create a copy of an existing array often arises. Understanding the optimal approach to copying such arrays is crucial to maintain data integrity and avoid pitfalls.

In the given scenario, a 2D array of integers, matrix, is to be copied into a local variable, myInt, for editing purposes. While a manual approach is possible, it can be error-prone and inefficient.

Copy Techniques

Instead, Java offers two recommended techniques for copying 2D arrays: using clone() or System.arraycopy().

Using clone()

The clone() method creates a shallow copy of an array, where the original array and the copy reference the same underlying elements. For a 2D array like matrix, this involves:

<code class="java">int[][] myInt = new int[matrix.length][];
for (int i = 0; i < matrix.length; i++)
    myInt[i] = matrix[i].clone();</code>

This approach is simple but only creates a copy of the references, not the elements themselves. If any elements in matrix are modified, the corresponding elements in myInt will be affected as well.

Using System.arraycopy()

The System.arraycopy() method performs a deep copy, copying the actual values of the elements rather than just the references. For a 2D array:

<code class="java">int[][] myInt = new int[matrix.length][];
for (int i = 0; i < matrix.length; i++) {
    int[] aMatrix = matrix[i];
    int aLength = aMatrix.length;
    myInt[i] = new int[aLength];
    System.arraycopy(aMatrix, 0, myInt[i], 0, aLength);
}</code>

This method requires a bit more work as it creates new arrays for each row, but it ensures that myInt is an independent copy. Any modifications made to myInt will not affect matrix.

Summary

While manually copying 2D arrays is possible, it is highly recommended to use the clone() or System.arraycopy() methods for efficiency, accuracy, and convenience. This ensures that the copied array (myInt) is properly isolated from the original array (matrix), allowing for independent modifications without the risk of unintended side effects.

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