Can You Change a Java String?

I read in a book that once you have created a Java String, you cannot change it so I decided to try it out myself:

andrew@UBUNTU:~/Java$ cat string_test.java
public class string_test
  {
  public static void main(String args[])
    {
    String str1 = "Andrew ";
    str1 = str1 + "was here";
    System.out.println("str1 = " + str1);
    }
  }
andrew@UBUNTU:~/Java$ javac string_test.java
andrew@UBUNTU:~/Java$ java string_test
str1 = Andrew was here
andrew@UBUNTU:~/Java$

At first glance, it looks as if you CAN change a String variable so I did a bit more reading. It seems that when you change a String, you are not altering the original variable. You are really creating a new variable to hold the updated value. If I can find some way to prove or disprove this statement, I will return to this post and update it accordingly.

How to Concatenate Strings in Java

This example shows how to concatenate strings i.e. how to join them together:

andrew@UBUNTU:~/Java$ cat prog38.java
public class prog38
{
public static void main (String args[])
  {
  String first_name = "Andrew";
  String surname = "Reid";
  String full_name = first_name + " " + surname;
  System.out.println ("full_name = " + full_name);
  }
}
andrew@UBUNTU:~/Java$ javac prog38.java
andrew@UBUNTU:~/Java$ java prog38
full_name = Andrew Reid
andrew@UBUNTU:~/Java$

How to Extract a Character from a String in Java

This example shows how to define a string then extract the character at a given position in that string. It does this using the String.charAt() method. Note that character positions are numbered from zero, not one. The first part uses a string variable whereas the second uses a string literal:

andrew@UBUNTU:~/Java$ cat prog37.java
public class prog37
{
public static void main (String args[])
  {
  String Andrews_name = "Andrew";
  char first_letter = Andrews_name.charAt(0);
  System.out.println
   ("1st letter of Andrew = " + first_letter);
  char fourth_letter = "Andrew".charAt(3);
  System.out.println
   ("4th letter of Andrew = " + fourth_letter);
  }
}
andrew@UBUNTU:~/Java$ javac prog37.java
andrew@UBUNTU:~/Java$ java prog37
1st letter of Andrew = A
4th letter of Andrew = r
andrew@UBUNTU:~/Java$