CS 1054: Laboratory Exercise 9

Objective

This exercise is to familiarize you with some of the String methods in Java as well as the concepts of cascading and composition.

To Receive Credit

Show the TA your working program before leaving class.

Activities

Within Eclipse, create a new Project and call it Lab9. Within it, create a class called StringMethods.
In Java, the String class has several methods. The ones we will use in this exercise are:
1. toUpperCase
2. toLowerCase
3. length
4. trim
5. concat
6. substring
If you need more help with these methods, you can always refer to the Java API documentation.

Type in or copy/paste the following simple program:

public class StringMethods {
   public static void main(String[] arg) {
      String poem1 = "	Tell me not, in mournful numbers "; //use a tab 
      String poem2 = "Life is but an empty dream! ";
      String poem3 = "For the soul is dead that slumbers, ";
      String poem4 = "And things are not what they seem.";

      System.out.println (poem1);
   }  // end main
} // end StringMethods

By modifying the above program, add the necessary code to accomplish the following. Make one change at a time and run the program after each modification. Keep adding modifications to the program for each task so that your final program implements all of the tasks below. Before running the program, don’t forget to modify the Java Target in the Edit->Java Application Release Settings to be the name of the file/class: StringMethods.
1. Print poem1 in all uppercase.
2. Print poem1 in all lowercase.
3. Print the length of poem1 by using the appropriate String method to calculate the length. Print the length in the following format: "The length of poem1 is x" where x is the length. (Hint: think of the difference between println and print.)
4. Use the appropriate String method to remove the tab from the beginning of poem1 and print the resulting String.
5. Using the appropriate String method, append poem2 on to the end of poem1 and print the result.
6. Using the appropriate String method (hint: use only 1 argument), print only the phrase "in mournful numbers" from poem1.
7. Using the appropriate String method, print only the phrase "me not," from poem1.
8. Create a new String using part of poem1 that reads "Students sigh, in mournful numbers". Print this new String. (Hint: You may need to create new variables to hold intermediate results, including possibly the phrase "Students sigh").
There are two techniques that can be used when building a new String from three or more Strings: 1. Cascading 2. Composition
Cascading is the process of sending a message to an object to create a new object, which in turn is sent a message to create another new object, which in turn is sent a message to create yet another new object, and so on. The results of messages are used as receivers of additional messages.
```
 
intitials = firstInit.concat(middleInit).concat(lastInit);
            
```
In this example, a concat message (with middleInit as argument) is sent to firstInit. The firstInit object returns a reference to a new String object ("JF"). Another concat message (with lastInit) is sent to the new String object whose reference was just returned. A reference to yet another new String object is returned.

Composition is the process of sending a message to an object to create a new object whose reference is used as an argument in a message. In turn, this may yield a reference to another new object, which then could be used as an argument in yet another message, and so on. The results of messages are used as arguments in additional message. An example can be found from code in the book that performs the same function as the code in the cascading example.
```
initials = firstInit.concat(middleInit.concat(lastInit));
            
```
In this example, a concat message (with lastInit as argument) is sent to middleInit. The middleInit object returns a reference to a new String object (consisting of the middle and last initials). The reference to this new object is sent as an argument in another concat message. A reference to yet another new String object is returned.
By modifying the StringMethods class you just created, use both the (a) cascade and (b) composition technique to concatenate the following segments of a poem into one String. Store the results in variables called cascade and composition respectively. Print the resulting Strings cascade and composition.
```
String poem1 = "Tell me not, in mournful numbers ";
String poem2 = "Life is but an empty dream!  ";
String poem3 = "For the soul is dead that slumbers, ";
String poem4 = "And things are not what they seem.";
				
```