Why is this an issue?

The JDK provides a set of built-in methods to copy the contents of an array into another array. Using a loop to perform the same operation is less clear, more verbose and should be avoided.

Exceptions

The rule detects only the most idiomatic patterns, it will not consider loops with non-trivial control flow. For example, loops that copy array elements conditionally are ignored.

How to fix it

You can use:

• Arrays.copyOf to copy an entire array into another array
• System.arraycopy to copy only a subset of an array into another array
• Arrays.asList to create a new list with the contents of the array
• Collections.addAll to add the elements of a collection into another collection

Note that Arrays.asList returns a fixed-size List, so further steps are required if a non-fixed-size List is needed.

Code examples

Noncompliant code example

public void copyArray(String[] source){
  String[] array = new String[source.length];
  for (int i = 0; i < source.length; i++) {
    array[i] = source[i]; // Noncompliant
  }
}

public void copyList(List<String> source) {
  List<String> list = new ArrayList<>();
  for (String s : source) {
    list.add(s); // Noncompliant
  }
}

Compliant solution

public void copyArray(String[] source){
  String[] array = Arrays.copyOf(source, source.length);
}

public void copyList(List<String> source) {
  List<String> list = new ArrayList<>();
  Collections.addAll(list, source);
}

public void makeCopiesConditional(int[] source) {
  int[] dest = new int[source.length];
  for (int i = 0; i < source.length; i++) {
    if (source[i] > 10) {
      dest[i] = source[i];  // Compliant, since the array elements are conditionally copied to the dest array
    }
  }
}

Resources

Documentation

• docs.oracle - Arrays.copyOf documentation
• docs.oracle - Arrays.asList documentation
• docs.oracle - System.arraycopy documentation