Is there any possibility to check the previous and next element in foreach loop?

Question

in java using for each how to check previous and next elements. Is there any possibility to check previous and next element in for each loop

Answer 1

No.

The "for each" construct uses Iterator underneath, which only has a next() and hasNext() functions. No way to get previous().

Lists have a ListIterator which does allow looking at the previous element, but "for each" doesn't know how to use it. The only solution is therefore to remember the previous element in a separate variable, or just use a simple counting loop like this: for(int i=0;i< foo.length();i++).

Answer 2

Using "for each" only has next() and hasNext() methods, so it doesn't provides methods for reverse traversing or extracting elements.

Considering you have a ArrayList of Strings, You can use java.util.ListIterator which provides methods such as hasPrevious() and previous()

Below is the sample of how it can be used . ** Read the comments in side of code as it contains important details for using these methods.**

        ArrayList<String> mylist = new ArrayList<>();

        ListIterator<String> myListIterator = mylist.listIterator();

        myListIterator.hasNext(); // Returns: true if list has next element
        myListIterator.next(); // Returns: next element , Throws:NoSuchElementException - if the iteration has no next element
        myListIterator.hasPrevious(); // Returns: true if list has previous element
        myListIterator.previous(); //Returns: the previous element in the list , Throws: NoSuchElementException - if the iteration has no previous element

Hope this helps.

PS : You should have posted the code which you have done so far, posting question on stackoverflow which does not contain anything to show your effort is really BAD.

Answer 3

What would be the purpose of this?

Instead of a foreach you should probably use a for loop and indexing

for(int i=0;i<lenght;i++) {
    list[i-1].dostuff //previous
    list[i].dostuff //current
    list[i+1].dostuff //next item
}

and don't forget to check if the next item and previous exists.

Answer 4

Some of the limitations of for Each loop.Can read the whole article for clear overview https://www.geeksforgeeks.org/for-each-loop-in-java/

Also,This can be one way:

    public class Main
{
    public static void main(String[] args) {
    String[] arr={"a","b"};
    String next="";
    String current="";
    String prev="";

    for(int i=0;i<arr.length;i++){

        //previousElement
        if(i>0){ 
            prev=arr[i-1] ;
            System.out.println("previous: "+prev);
       }else{
           prev="none";
          System.out.println("previous: "+prev);
               }

         //currentElement      
        current=arr[i];
       System.out.println(" current: "+current);

       //nextElement
      if(i<arr.length-1){
          next=arr[i+1];
          System.out.println(" next: "+next);
              }else{
                  next="none";
                  System.out.println(" next: "+next);
                              }
                }
  }
}

Attaching the output also:

P.S. can check the code on https://www.onlinegdb.com/online_java_compiler