LinkedHashSet and HashSet

package justtest;

import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.Set;

public class TestSet {

    public static void main(String[] args) {

     /** Create set that retains Order-of-Insertion */
      Set set = new LinkedHashSet();
      set.add("1");
      set.add("2");
      set.add("3");
      set.add("2");
      for (Iterator it = set.iterator(); it.hasNext();) {
          System.out.println(it.next()); //1,2,3
      }

      /** Create set that does not retain Order-of-Insertion */
      Set set2 = new HashSet();
      set2.add("1");
      set2.add("2");
      set2.add("3");
      set2.add("2");
      set2.add("3");
      for (Iterator it = set2.iterator(); it.hasNext();) {
          System.out.println(it.next()); //3,2,1
      }
   }
}

Java regular expression (edit date)

package com.mmm.http;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

import com.mmm.model.AppField;

public class EditDate {

public static String editDate(String date, int type) {
  String msg = null;
  String patrn = pattern(type);
  Pattern pat = Pattern.compile(patrn);
  Matcher matcher = pat.matcher(date);
  if (!matcher.find()) {
      msg = "Invalid date format.";
  }
  return msg;
}

public static String pattern(int type) {
  String p = "";
  switch (type) {
  case AppField.DATE_ISO:
     //must be nnnn-nn-nn
     p = "\\d{4}-\\d{2}-\\d{2}"; // ISO
     break;
  case AppField.DATE_USA:
     p = "\\d{2}/\\d{2}/\\d{4}";
     break;
  case AppField.DATE_EUR:
     p = "\\d{4}.\\d{2}.\\d{2}";
     break;
  default:
     p = "\\d{4}-\\d{2}-\\d{2}"; // ISO
     break;
  }
  p = "^" + p + "$"; //important!
  return p;
}

public static void main(String[] args) {
  System.out.println("msg=" + editDate("2000-10-10", 24));
  System.out.println("msg=" + editDate("22/12/1999", 25));
  System.out.println("msg=" + editDate("11/11/99", 20));
}
}


Some Predefined Character Classes:

.      Any character (may or may not match line terminators)
\d     A digit: [0-9]
\D     A non-digit: [^0-9]
\s     A whitespace character: [ \t\n\x0B\f\r]
\S     A non-whitespace character: [^\s]
\w     A word character: [a-zA-Z_0-9]
\W     A non-word character: [^\w]