Java - Iterating over every two elements in a list

Question

What\'s the best way to iterate over a list while processing 2 elements at the same time?

Example:

List strings = Arrays.asList(\"item          


        

Answer 1

List<String> strings = Arrays.asList("item 1", "item 2", "item 3", "item 4");
for(int i = 0; i < strings.size(); i++){
    if(i½2 = 0){
        String first = strings.get(i);
        System.out.print("First [" + first + "] ");
    }else{
         String second = strings.get(i + 1);
         System.out.println("- Second [" + second + "]");
    }
}

Answer 2

Just increase i by 2:

for(int i = 0; i < strings.size(); i += 2) {

Answer 3

For performance, I will recommend you to compute the size of the list only one and not create a new string at each new loop.

List<String> strings = Arrays.asList("item 1", "item 2", "item 3", "item 4");
int length = strings.size();
String first, second = null;
for(int i = 0; i < length; i += 2){
    ...
}

Answer 4

for(int i = 0; i < strings.size(); i++){
    String first = strings.get(i++);
    String second = null;
    if(strings.size() > i){
        second = strings.get(i);
    }
    System.out.println("First [" + first + "] - Second [" + second + "]");
}

Answer 5

I created the following method using a Java8 BiConsumer:

public static <T> void tupleIterator(Iterable<T> iterable, BiConsumer<T, T> consumer) {
    Iterator<T> it = iterable.iterator();
    if(!it.hasNext()) return;
    T first = it.next();

    while(it.hasNext()) {
        T next = it.next();
        consumer.accept(first, next);
        first = next;
    }
}

use it like this:

List<String> myIterable = Arrays.asList("1", "2", "3");
tupleIterator(myIterable, (obj1, obj2) -> {
    System.out.println(obj1 + " " + obj2);
});

This will output:

1 2
2 3

Answer 6

You need to modify and increment i for the second value, modify the statement:

second = strings.get(i + 1);

to

second = strings.get(++i);

This will increment the i as well, since this seems to be the desired behaviour.

So your code would be:

List<String> strings = Arrays.asList("item 1", "item 2", "item 3", "item 4");
for(int i = 0; i < strings.size(); i++){
    String first = strings.get(i);
    String second = null;
    if(strings.size() > i + 1){
        second = strings.get(++i); //Change here
    }
    System.out.println("First [" + first + "] - Second [" + second + "]");
}