Java: how to get Iterator<Character> from String [duplicate]

Question

I need a Iterator<Character> from a String object. Is there any available function in Java that provides me this or do I have to code my own?

Answer 1

One option is to use Guava:

ImmutableList<Character> chars = Lists.charactersOf(someString); UnmodifiableListIterator<Character> iter = chars.listIterator(); 

This produces an immutable list of characters that is backed by the given string (no copying involved).

If you end up doing this yourself, though, I would recommend not exposing the implementation class for the Iterator as a number of other examples do. I'd recommend instead making your own utility class and exposing a static factory method:

public static Iterator<Character> stringIterator(final String string) {   // Ensure the error is found as soon as possible.   if (string == null)     throw new NullPointerException();    return new Iterator<Character>() {     private int index = 0;      public boolean hasNext() {       return index < string.length();     }      public Character next() {       /*        * Throw NoSuchElementException as defined by the Iterator contract,        * not IndexOutOfBoundsException.        */       if (!hasNext())         throw new NoSuchElementException();       return string.charAt(index++);     }      public void remove() {       throw new UnsupportedOperationException();     }   }; } 

Answer 2

It doesn't exist, but it's trivial to implement:

class CharacterIterator implements Iterator<Character> {      private final String str;     private int pos = 0;      public CharacterIterator(String str) {         this.str = str;     }      public boolean hasNext() {         return pos < str.length();     }      public Character next() {         return str.charAt(pos++);     }      public void remove() {         throw new UnsupportedOperationException();     } } 

The implementation is probably as efficient as it gets.