Comparator uses a Collator to determine the proper, case-insensitive lexicographical ordering of two strings. : Comparator Interface « Collections « Java Tutorial

1. Java Tutorial
2. Collections
3. Comparator Interface

import java.text.Collator;
import java.util.Comparator;

class IgnoreCaseComp implements Comparator<String> {
  Collator col;

  IgnoreCaseComp() {
    col = Collator.getInstance();

    col.setStrength(Collator.PRIMARY);
  }

  public int compare(String strA, String strB) {
    return col.compare(strA, strB);
  }
}