Strings

Many programs manipulate not just numbers but text. Java stores text in string variables. They are declared and assigned in a manner similar to a numeric variable, and the sequence may have any length. (A string may even have length zero. Such a string is called an empty string, and it is denoted as "".) For example,

   String name = "Joan Wilson";

assigns the 11 characters enclosed in quotes to the variable name.

   String temp = name; 

assigns the content of variable name to variable temp

   System.out.println(name); 

displays the contents of variable name on the standard output stream.

Learning Exercises with Strings

1. Concatenation

   Given:

      String firstName = "Jane";
      String lastName = "Doe";
      String name;
   

   What value will name contain after

         name = firstName + lastName;
   

   How could the preceding be revised to give a better result?

2. substrings

   The primary difference between strings and numeric data types is that any portion of the characters in a string variable is itself a string variable. Such a portion is called a substring.

   What will be the resulting substring in the following examples? If invalid, give a corrected version of the call to substring.

   String name = "John Smith" String firstName = name.substring(0, 4);

   String name = "John Smith" String lastName = name.substring(5, 6);

3. Extracting substrings

   Consider the following code fragment

         String name = "George Bush";
   
         String x = name.substring(6, 7);
         String y = x + x + x + x + ".";
   

   What value has the String y? What value has the expression y.length()

4. Manipulating Strings

   Using substring and concatenation, write a program containing a sequence of commands that will extract characters from name = "albert einstein" to make newName = "bertie"

5. Who's There

   Write a program that asks the user for a name and then prints out Hello 'name'. E.g. a sample run might look like

   $ java Who Enter your name: James    Hello James $

   The command Console.readString() will read in a String (such as a name)

6. Usernames

   Write a program which when given a first name, second name and a number, will print out a dcu username. E.g. given mickey mouse 3, the program will print mmouse3 Note: to make an username, take

   1. the first letter of your first name
   2. add your surname
   3. add the number

   Note 2: Actually it's slightly different if the surname is long, but you can ignore that problem for the moment.

7. Email Addresses

   Write a program which when given a first name, second name and a number, will print out a dcu email address. E.g. given mickey mouse 3, the program will print mickey.mouse3@mail.dcu.ie Note: to make an email address, take

   1. the first name
   2. concatenate it with your surname
   3. separate the two with a dot
   4. add the number
   5. add the @mail.dcu.ie part

8. Optional exercise

   Write a program that reads a number greater than or equal to 1000, and less than a million. Print the number with a comma separating the thousands. Here is a sample interaction with the user:

   $ java Comma Please enter a number >= 1000: 23456    23,456 $

   Hint: think of the end of the number. Here's another hint

9. Optional exercise

   Write a program that reads a number from the user. The number contains a correctly positioned comma. The program should print the number with the comma removed, e.g.

   $ java DeCommify Please enter a number >= 1000: 12,345    12345 $

   Note that there is no comma in the output.

   Here's a hint.

Hint eile: read the question carefully: the number will be correctly formatted and will contain a comma.