1. Convert Java util.Date to sql.Date

This piece of code shows how to convert a java util Date into a sql Date for use in database.

java.util.Date util_date = new java.util.Date();
java.sql.Date sql_date = new java.sql.Date(util_date.getTime());

2. Convert Array to Map

import java.util.Map;
import org.apache.commons.lang.ArrayUtils;


public class Main {


public static void main(String[] args) {
String[][] states = { { "UP", "Lucknow" }, { "MP", "Bhopal" },
  { "Maharashtra", "Mumbai" }};


  Map stateCapitals = ArrayUtils.toMap(states);


System.out.println("Capital of Maharashtra is " + stateCapitals.get("Maharashtra"));
System.out.println("Capital of UP is " + stateCapitals.get("UP"));
}
}

3. Regular Expression for validating an email

 private final static Pattern EMAIL_PATTERN = Pattern
            .compile("^([_A-Za-z0-9-\\+]*[a-zA-Z]+[_A-Za-z0-9-\\+]*)(\\.[_A-Za-z0-9-]+)*@"
                    + "[A-Za-z0-9-]+(\\.[A-Za-z0-9]+)*(\\.[A-Za-z]{2,})$");

       private boolean isEmail(String value)
    {
        return EMAIL_PATTERN.matcher(value).matches();
    }

4. Regular Expression for validating a password

private final static Pattern PASSWORD_PATTERN = Pattern
            .compile("((?=.*\\d)(?=.*[a-z])(?=.*[A-Z])(?=.*[@#$%]).{6,20})");


private boolean isValidPassword(String value)
    {

        int passwordLength = value.length();
        if(passwordLength >= 6) {
            return true;
        } else {
            return false;
        }
    }

5. Convert String to date

java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);

6. Always try to use primitive datatypes instead of wrapper class

int a = 5;
int b = 5;

Integer a1 = new Integer(5);
Integer b1 = new Integer(5);

System.out.println(a==b);
System.out.println(a1==b1);

The first sysout will print true whereas the second one will print false. The problem is when comparing two wrapper class objects we cant use == operator. It will compare the reference of object and not its actual value.

Also if you are using a wrapper class object then never forget to initialize it to a default value. As by default all wrapper class objects are initialized to null.

Hope it helps someone!