Java Enhanced For Statement – How to Use with Arrays and Get an Iterator

arraysforeachiteratorjava

Given the following code snippet:

int[] arr = {1, 2, 3};
for (int i : arr)
    System.out.println(i);

I have the following questions:

How does the above for-each loop work?
How do I get an iterator for an array in Java?
Is the array converted to a list to get the iterator?

Best Answer

If you want an Iterator over an array, you could use one of the direct implementations out there instead of wrapping the array in a List. For example:

Apache Commons Collections ArrayIterator

Or, this one, if you'd like to use generics:

com.Ostermiller.util.ArrayIterator

Note that if you want to have an Iterator over primitive types, you can't, because a primitive type can't be a generic parameter. E.g., if you want an Iterator<int>, you have to use an Iterator<Integer> instead, which will result in a lot of autoboxing and -unboxing if that's backed by an int[].

Related Solutions

Java Enhanced For Loop Syntax

Enhanced for loop:

for (String element : array) {

    // rest of code handling current element
}

Traditional for loop equivalent:

for (int i=0; i < array.length; i++) {
    String element = array[i]; 

    // rest of code handling current element
}

Take a look at these forums: https://blogs.oracle.com/CoreJavaTechTips/entry/using_enhanced_for_loops_with

http://www.java-tips.org/java-se-tips/java.lang/the-enhanced-for-loop.html

Java – Enhanced For-Loop Does Not Accept Iterator

The enhanced for loop was part of JSR 201. From that page, you can download the proposed final draft documents, which include a FAQ section directly addressing your question:

Appendix I. Design FAQ

Why can't I use the enhanced for statement with an Iterator (rather than an Iterable or array)?

Two reasons: (1) The construct would not provide much in the way on syntactic improvement if you had an explicit iterator in your code, and (2) Execution of the loop would have the "side effect" of advancing (and typically exhausting) the iterator. In other words, the enhanced for statement provides a simple, elegant, solution for the common case of iterating over a collection or array, and does not attempt to address more complicated cases, which are better addressed with the traditional for statement.

Why can't I use the enhanced for statement to:

remove elements as I traverse a collection ("filtering")?

simultaneously iterate over multiple collections or arrays?

modify the current slot in an array or list?

See Item 1 above. The expert group considered these cases, but opted for a simple, clean extension that dose(sic) one thing well. The design obeys the "80-20 rule" (it handles 80% of the cases with 20% of the effort). If a case falls into the other 20%, you can always use an explicit iterator or index as you've done in the past.

In other words, the committee chose to limit the scope of the proposal, and some features that one could imagine being part of the proposal didn't make the cut.

Best Answer

Related Solutions

Java Enhanced For Loop Syntax

Java – Enhanced For-Loop Does Not Accept Iterator

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