How to Efficiently Copy a Byte Array with Null Padding to a Smaller Byte Array

Question

How can I efficiently copy a byte array, which contains null bytes at the end, to a smaller byte array?

byte[] sourceArray = new byte[] { 1, 2, 3, 0, 0, 0 }; // Source byte array
byte[] smallerArray = new byte[3]; // Destination byte array
System.arraycopy(sourceArray, 0, smallerArray, 0, smallerArray.length); // Efficient copy

Answer

Copying a byte array with null padding to a smaller array involves considering how many valid bytes are actually needed, as well as ensuring you do not transfer unnecessary nulls. This process can be efficiently managed using Java's `System.arraycopy` method to reduce both time and space complexity.

int lengthToCopy = 0;
for (int i = sourceArray.length - 1; i >= 0; i--) {
    if (sourceArray[i] != 0) {
        lengthToCopy = i + 1;
        break;
    }
}
byte[] smallerArray = new byte[lengthToCopy];
System.arraycopy(sourceArray, 0, smallerArray, 0, lengthToCopy); // Efficiently copy to smaller array.

Causes

  • The source byte array may contain padded null bytes that should not be transferred to the destination array.
  • Choosing the correct size for the destination array is crucial to avoid ArrayIndexOutOfBounds exceptions.

Solutions

  • Use `System.arraycopy` to minimize overhead and copy only relevant data up to the desired length.
  • Determine the last non-null index in the source array to define how many bytes should be copied.

Common Mistakes

Mistake: Not resizing the destination array based on non-null byte count.

Solution: Always check the actual data length before copying to ensure you allocate the correct size.

Mistake: Using a manual loop to copy bytes which is inefficient compared to built-in methods.

Solution: Employ `System.arraycopy` for better performance and reduced code complexity.

Helpers

  • byte array copy
  • Java byte array
  • copy with null padding
  • efficient array copy

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