Java: how to get Iterator from String [duplicate]

Answer 1

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.

Answer 2

Stealing from somebody else in another answer, this is probably the best direct implementation (if you're not going to use guava).

/**
 * @param string
 * @return list of characters in the string
 */
public static List<Character> characters(final String string) {
return new AbstractList<Character>() {
        @Override
    public Character get(int index) {
            return string.charAt(index);
        }

        @Override
    public int size() {
            return string.length();
        }
    };
}

Answer 3

This can be done with a little help from Apache Commons Lang (if you don't want to use Guava, and want a true java.util.Iterator.

private static Iterator<Character> iterator(String string) {
    return Arrays.asList(ArrayUtils.toObject(string.toCharArray())).iterator();
}

Answer 4

for (char c : myString.toCharArray()) {

}

Answer 5

CharacterIterator it = new StringCharacterIterator("abcd"); 
// Iterate over the characters in the forward direction 
for (char ch=it.first(); ch != CharacterIterator.DONE; ch=it.next())
// Iterate over the characters in the backward direction 
for (char ch=it.last(); ch != CharacterIterator.DONE; ch=it.previous()) 

Answer 6

Short answer: No, you have to code it.

Long answer: List and Set both have a method for obtaining an Iterator (there are a few other collection classes, but probably not what your looking for). The List and Set interfaces are a part of the Collections Framework which only allow for adding/removing/iterating Objects like Character or Integer (not primitives like char or int). There is a feature in Java 1.5 called auto-boxing that will hide this primitive to Object conversion but I don't recommend it and it won't provide what you want in this case.

An alternative would be to wrap the String in a class of your own that

implements Iterator<Character>

but that might be more work than it is worth.

Here is a code snippet for doing what you want:

String s = "";
List<Character> list = new ArrayList<Character>(s.length());
for (int i = 0; i < s.length(); i++) {
    // note that Character.valueOf() is preferred to new Character()
    // you can omit the Character.valueOf() method
    // and Java 1.5+ will auto-box the primitive into an Object
    list.add(Character.valueOf(s.charAt(i)));
}
Iterator<Character> iterator = list.iterator();