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  • 6 useful code chunks for java coders.

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    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());
    1. 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"));
    }
    }
    1. 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();
        }
    
    
    1. 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;
            }
        }
    
    1. Convert String to date
    java.util.Date = java.text.DateFormat.getDateInstance().parse(date String);
    
    1. 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!

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