How can I iterate through the unicode codepoints of a Java String?

Yes, Java uses a UTF-16-esque encoding for internal representations of Strings, and, yes, it encodes characters outside the Basic Multilingual Plane (BMP) using the surrogacy scheme.

If you know you'll be dealing with characters outside the BMP, then here is the canonical way to iterate over the characters of a Java String:

final int length = s.length();for (int offset = 0; offset < length; ) {   final int codepoint = s.codePointAt(offset);   // do something with the codepoint   offset += Character.charCount(codepoint);}

Java 8 added CharSequence#codePoints which returns an IntStream containing the code points.You can use the stream directly to iterate over them:

string.codePoints().forEach(c -> ...);

or with a for loop by collecting the stream into an array:

for(int c : string.codePoints().toArray()){    ...}

These ways are probably more expensive than Jonathan Feinbergs's solution, but they are faster to read/write and the performance difference will usually be insignificant.

Thought I'd add a workaround method that works with foreach loops (ref), plus you can convert it to java 8's new String#codePoints method easily when you move to java 8:

You can use it with foreach like this:

 for(int codePoint : codePoints(myString)) {   .... }

Here's the method:

public static Iterable<Integer> codePoints(final String string) {  return new Iterable<Integer>() {    public Iterator<Integer> iterator() {      return new Iterator<Integer>() {        int nextIndex = 0;        public boolean hasNext() {          return nextIndex < string.length();        }        public Integer next() {          int result = string.codePointAt(nextIndex);          nextIndex += Character.charCount(result);          return result;        }        public void remove() {          throw new UnsupportedOperationException();        }      };    }  };}

Or alternately if you just want to convert a string to an array of int codepoints (if your code could use a codepoint int array more easily) (might use more RAM than the above approach):

 public static List<Integer> stringToCodePoints(String in) {    if( in == null)      throw new NullPointerException("got null");    List<Integer> out = new ArrayList<Integer>();    final int length = in.length();    for (int offset = 0; offset < length; ) {      final int codepoint = in.codePointAt(offset);      out.add(codepoint);      offset += Character.charCount(codepoint);    }    return out;  }

Thankfully uses "codePointAt" which safely handles the surrogate pair-ness of UTF-16 (java's internal string representation).