How to Create a Deep Copy of a Two-Dimensional Array in Java?

Copying Two-Dimensional Arrays in Java

Copying multidimensional arrays in Java can be tricky, as assigning one array to another simply creates a reference to the original data rather than a true copy. To create a genuine duplicate, you need to allocate new memory and copy the elements individually.

In your case, you have two methods, old() and keepold(), to copy the current array into old and vice versa. However, when you update current, the changes are also reflected in old because they both reference the same underlying data.

To create a true copy, you can use the following steps:

1. Create a New Array: Allocate a new two-dimensional array with the same dimensions as the original.
2. Copy the Elements: Iterate through the original array and assign each element to the corresponding position in the new array.

Using streams API (Java 8 ), you can simplify this process:

<code class="java">int[][] copy = Arrays.stream(matrix).map(int[]::clone).toArray(int[][]::new);</code>

This line uses the map() method to create a new array for each row, then the clone() method to copy each row, and finally the toArray() method to create a new two-dimensional array from the cloned rows.

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