How Can I Efficiently Remove Objects from a Java Array?

Removing Objects from an Array in Java

In Java, arrays are fixed-length collections of elements. When you need to remove an object from an array, there is no straightforward built-in method to do so.

Consider an array of strings:

String[] foo = { "a", "cc", "a", "dd" };

Solution: Array to List and Back

One approach to remove objects from an array is to convert it to a list, modify the list, and then convert it back to an array.

List<String> list = new ArrayList<>(Arrays.asList(foo));
list.removeAll(Arrays.asList("a"));
foo = list.toArray(foo);

This process retains the original array's size, with the elements after the last remaining element set to null.

Solution: New Array from List

If you want a new array exactly the size needed, you can do the following:

foo = list.toArray(new String[list.size()]);

Using Reusables

For frequent usage, you might consider creating a pre-defined empty string array constant:

private static final String[] EMPTY_STRING_ARRAY = new String[0];

Then, the removal function can be rewritten as:

List<String> list = new ArrayList<> ();
Collections.addAll(list, foo);
list.removeAll(Arrays.asList("a"));
foo = list.toArray(EMPTY_STRING_ARRAY);

Alternatively, you can use the approach suggested by cynicalman:

foo = list.toArray(new String[list.size()]);

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