[Java] Make variables in extended for statement and for Each statement immutable

When declared normally

If you declare the extended for statement and for Each statement normally, it will be as follows. Since it is not declared final, it can be reassigned (normal for statements are skipped because reassignment is essential in principle).

List<Integer> intList = Arrays.asList(1, 2, 3, 4);

for(int i : intList) {
    i = 0; //Can be rewritten

intList.forEach(it -> {
    it = 0; //Can be rewritten

In this article, we will rewrite these contents into a non-reassignable form.

Make the variable immutable

For extended for statement

You can make it ʻimmutable by declaring it with final`.

for(final int i : intList) {
    i = 0; //Since it is declared final, it cannot be reassigned and a compile error occurs.

For foreach statement

You can make the argument final by specifying the type in parentheses as shown below.

intList.forEach((final int it) ->
    it = 0; //Since it is declared final, it cannot be reassigned and a compile error occurs.

Another solution

For the time being, the argument can be final even when implementing it as an anonymous class.

Consumer<Integer> finalConsumer = new Consumer<Integer>() {
    public void accept(final Integer it) {
        it = 0; //Since it is declared final, it cannot be reassigned and a compile error occurs.


When this article was first published, the title and content was "** Indexes can be immutable only for extended for statements, extended for statements, and forEach statements **", but @ saka1029 pointed out. As you can see, this was an error, so I completely rewrote both the title and content.

Thank you for pointing out @ saka1029.

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