• 2.5.1 String objects
• 2.5.2 StringBuffer class
  • 2.5.2.1 Exercise
  • 2.5.2.2 Exercise

2.5 Strings

2.5.1 String objects

• Java provides a String class to deal with sequences of characters.

  String username = "Fred Flinstone";
  

• The String class provides a variety of methods to operate on String objects.
• The equals() method is used to compare Strings.
• The length() method returns the number of characters in the String.
• The + operator is used for String concatenation.
• String objects are read-only (also called immutable).
• In the example below, the second assignment gives a new value to the object reference str, not to the contents of the string:

  str = "Fred";
  str = "Barney"
  

• An array of char is not a String.

2.5.2 StringBuffer class

• The StringBuffer class is often used when you need the ability to modify strings in your programs.
• Manipulating a StringBuffer can be faster than creating-re-creating String objects during heavy text manipulation.
• StringBuffer objects are mutable.
• Useful methods include append(), charAt(), indexOf(), insert(), length(), and replace().

2.5.2.1 Exercise

• What is the output of the following class?

  class StringTest {
     public static void main (String args[]) {
        String str1 = null;
        String str2 = null;
        str1 = "Fred";
        str2 = str1;
        System.out.println("str1: " + str1);
        System.out.println("str2: " + str2);
        
        str1 = "Barney";
        System.out.println("str1: " + str1);
        System.out.println("str2: " + str2);
     }
  }
  

2.5.2.2 Exercise

• Modify the Hello application so it reads the a user's name from the command line, and writes the user's name as part of the output.
• Here is the source code for the original class:

  public class Hello
  {
    public static void main(String[] args) {
      System.out.println( "Hello, world" );
    }
  }
  

• Assuming that the users name is Al, after the changes the output of the program should be:

  Hello, Al
  

Up: 2. Day 2: The Previous: 2.4 Arrays Next: 2.6 Comments and Javadoc   Contents