CODEWITHSUNDEEP
javaloops
nano_nano
nano_nano

Reputation: 12523

Generic for-loop: Is there a way to get iteration information?

I am used to implement loops with generics like that:

for (final Dog lDog : lAllDog) {
   ...
}

Unfortunality for another business case I need the current count of the iteration. I know I can solve this by coding somthing like that:

for (int i = 0 ; i < lAllDog.length(); i++) {
   System.out.println(i);
}

or 

int i = 0;
for (final Dog lDog : lAllDog) {
   ...
   i++;
}

but is there a way to get the current count of iteration with my first code example without declaring a new int or change the whole loop header?

Thx a lot

Upvotes: 5

Views: 1393

Answers (5)

ZhongYu
ZhongYu

Reputation: 19682

They say every problem in computer science can be solved by more indirection

class Indexed<T>
    int index;
    T value;

static <T> Iterable<Indexed<T>> indexed(Iterable<T> iterable){ ... }

for(Indexed<Dog> idog : indexed(dogs))
    print(idog.index);
    print(idog.value);

In java 8, we probably want to abstract this control pattern as

forEach(dogs, (index, dog)->{ 
    print(index);
    print(dog);
});

static <T> void forEach(Iterable<T> collections, Acceptor<T> acceptor){...}

interface Acceptor<T>
    void accept(int index, T value);

Upvotes: 1

Pragnani
Pragnani

Reputation: 20155

No, if your list has unique elements

May be you can try this

for (final Dog lDog : lAllDog) {

 int i=  lAllDog.indexOf(lDog);
}

Upvotes: 1

Zach Latta
Zach Latta

Reputation: 3331

No. The enhanced for loop doesn't hold an index. You'll have to introduce it yourself if you want one.

The reason is because it's based on Iterable interface. Essentially, it uses an iterator to loop through a collection.

Upvotes: 1

Charu Khurana
Charu Khurana

Reputation: 4551

No, there is no other to get count of iteration other than you described in your question. You'll have to use old way to have counter defined

Upvotes: 1

Brian Agnew
Brian Agnew

Reputation: 272297

Briefly, no. You have to use the indexing method to do that.

Upvotes: 5

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