How do I check if a string is empty or not?

package org.kodejava.example.commons.lang;

import org.apache.commons.lang.StringUtils;

public class EmptyStringCheckExample {
    public static void main(String[] args) {
        // Create some variable to hold some string that empty, contains only
        // white spaces and words.
        String one = "";
        String two = "\t\r\n";
        String three = "     ";
        String four = null;
        String five = "four four two";

        // We can use StringUtils class for checking if a string is empty or not
        // using StringUtils.isBlank() method. This method will return true if
        // the tested string is empty, contains white space only or null.
        System.out.println("Is one empty? " + StringUtils.isBlank(one));
        System.out.println("Is two empty? " + StringUtils.isBlank(two));
        System.out.println("Is three empty? " + StringUtils.isBlank(three));
        System.out.println("Is four empty? " + StringUtils.isBlank(four));
        System.out.println("Is five empty? " + StringUtils.isBlank(five));

        // On the other side, the StringUtils.isNotBlank() methods complement
        // the previous method. It will check is a tested string is not empty.
        System.out.println("Is one not empty? " + StringUtils.isNotBlank(one));
        System.out.println("Is two not empty? " + StringUtils.isNotBlank(two));
        System.out.println("Is three not empty? " + StringUtils.isNotBlank(three));
        System.out.println("Is four not empty? " + StringUtils.isNotBlank(four));
        System.out.println("Is five not empty? " + StringUtils.isNotBlank(five));

Here is the result:

Is one empty? true
Is two empty? true
Is three empty? true
Is four empty? true
Is five empty? false

Is one not empty? false
Is two not empty? false
Is three not empty? false
Is four not empty? false
Is five not empty? true