Java, How do I get current index/key in "for each" loop

Question

In Java, How do I get the current index for the element in Java?

for (Element song: question){
    song.currentIndex();         //<<want the current index.
}

In PHP you could do this:

foreach ($arr as $index => $value) {
    echo "Key: $index; Value: $value";
}

In PHP, you are using an associative array which is not synonymous Java's array. — squiguy, Jan 03 '13 at 01:36

score 391 · Accepted Answer · answered Aug 07 '10 at 18:24

391

You can't, you either need to keep the index separately:

int index = 0;
for(Element song : question) {
    System.out.println("Current index is: " + (index++));
}

or use a normal for loop:

for(int i = 0; i < question.length; i++) {
    System.out.println("Current index is: " + i);
}

The reason is you can use the condensed for syntax to loop over any Iterable, and it's not guaranteed that the values actually have an "index"

answered Aug 07 '10 at 18:24

Michael Mrozek

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This is indeed the correct answer semantically, for each loop can iterate through streaming data from a remote database which is being updated while you're iterating through its contents (if the used iterator actually does that) in which case there's no way of knowing the current index. Index is just a *view* to the data, not a property of data. – Esko Aug 07 '10 at 18:26
1

Although it might be no index, it would be very convenient to have some kind of iteration counter that you can access inside the loop. I guess such thing can hardly end in core java, more chances for some of the scripting languages. – akostadinov Apr 01 '13 at 11:11
As I was afraid, maybe in Java 12 they will add it as a feature to be proud of, as they recently did with lambdas and reading files with one-liners? (DISCLAIMER: I am (mostly) a Java programmer myself) – Andreas Tasoulas Dec 18 '14 at 12:37
1

@atas 2.5 years closer to Java 12... The index is definitely available, i.e. it's on the stack, if you're dealing with an array. It would be really cool if there was a keyword that would compile to a simple "ILOAD 2". If it's a List, it compiles to an iterator, which won't be able to give you an index. – Bjørn Vårdal Aug 02 '17 at 00:25

score 16 · Answer 2 · answered Aug 07 '10 at 18:24

16

In Java, you can't, as foreach was meant to hide the iterator. You must do the normal For loop in order to get the current iteration.

answered Aug 07 '10 at 18:24

TheLQ

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Saher Ahwal · Answer 3 · 2014-12-31T06:37:48.020

12

Keep track of your index: That's how it is done in Java:

 int index = 0;
    for (Element song: question){
        // Do whatever
         index++;
    }

edited Dec 31 '14 at 06:37

answered Aug 07 '10 at 18:56

Saher Ahwal

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That's true, but as much as I love the enhanced for-each loop introduced in Java5, doesn't supplying your own index defeat the purpose of simply using the traditional for-each construct? Using what's built into Java will often be more intuitive / readable (though not always) to the Java developer. – Michael M Jun 11 '17 at 19:39
6

7 years later... ( wow I can't believe it, time flies) , I agree with you @MichaelM 100%. – Saher Ahwal Jun 12 '17 at 18:16

score 10 · Answer 4 · edited Dec 16 '19 at 16:46

10

###################################################
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AVOID THIS
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/*for (Song s: songList){
    System.out.println(s + "," + songList.indexOf(s); 
}*/

it is possible in linked list.

you have to make toString() in song class. if you don't it will print out reference of the song.

probably irrelevant for you by now. ^_^

edited Dec 16 '19 at 16:46

Ele

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answered Nov 18 '13 at 18:30

EdenB

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Ugly hack...... – Pacerier Aug 08 '14 at 00:15
82

As people commented on http://stackoverflow.com/a/5200217, this is wrong if there are duplicate elements and is O(n²) slow. – Beni Cherniavsky-Paskin Feb 25 '15 at 12:45
33

Terrible, terrible, terrible. Please don't *ever* do this. – gabor Jun 12 '17 at 09:59
4

A wrong solution, indexOf returns the index of the first match element so if there are more than one it will return the index of the first one even if the loop is in the second one. – Ahmed Ibrahim Feb 05 '19 at 03:56
3

don't consider this as a solution, please remove the answer if possible, – Ahmed Hasn. Jul 10 '19 at 12:38

score 4 · Answer 5 · answered Aug 07 '10 at 19:25

4

Not possible in Java.

Here's the Scala way:

val m = List(5, 4, 2, 89)

for((el, i) <- m.zipWithIndex)
  println(el +" "+ i)

answered Aug 07 '10 at 19:25

Zeffer

89
1

Neat! See also https://stackoverflow.com/questions/7167253/is-there-a-java-equivalent-of-pythons-enumerate-function – Beni Cherniavsky-Paskin Feb 25 '15 at 12:48
1

I was thinking the same thing. I also love the Javascript syntax : `myArray.forEach((val, index) => console.log('VAL : ', val, 'INDEX : ', index) );` – Alex Jun 13 '18 at 09:36
question is about Java, not JVM : sorry but scala is out of scope. – Xavier D Feb 01 '21 at 16:31

score 2 · Answer 6 · answered Jan 03 '13 at 01:09

2

As others pointed out, 'not possible directly'. I am guessing that you want some kind of index key for Song? Just create another field (a member variable) in Element. Increment it when you add Song to the collection.

answered Jan 03 '13 at 01:09

likejudo

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Erik Brandsberg · Answer 7 · 2016-10-13T12:52:07.440

-5

Example from current code I'm working with:

int index=-1;
for (Policy rule : rules)
{   
     index++;
     // do stuff here
}

Lets you cleanly start with an index of zero, and increment as you process.

edited Oct 13 '16 at 12:52

answered May 13 '16 at 02:30

Erik Brandsberg

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Simply cumbersome. Start at zero and implement at the end. Unless you use continue in the body of the loop. – gabor Jun 12 '17 at 11:32

Java, How do I get current index/key in "for each" loop

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