Lab 5 Solution

MATERIAL COVERED


    • Exceptions
    • File reading and writing

Notes:
    • The three exercises are independent – you can do them in any order.
    • Only one of the three exercises is required.

    • The Bronze and Silver exercises are similar – both will read in an entire text file and write it out again in modified form. About 75% of the code is the same in the two exercises. If you do both of them, use a copy of your Bronze program as a starting point for your Silver program.





Adding line numbers to a file


    1. Begin with the supplied file TemplateLab5Bronze.java.

    2. Complete the main method so that it will read in the supplied file testLab5Bronze.txt and write out a modified version of this file as outputLab5Bronze.txt. (These two names are predefined for you as global constants.) The output file should be the same as the input file, except that every line should have a line number added to the front, in the format shown below.

The supplied file testLab5Bronze.txt contains:

This is the top line

The previous one is blank.
Short one.
This is the last one.

Your program should create an output file outputLab5Bronze.txt which contains:

    1: This is the top line

    2: 
    3: The previous one is blank.
    4: Short one.
    5: This is the last one.





Adding indentation to a Java file


    1. Begin with the supplied file TemplateLab5Silver.java.

    2. Complete the main method so that it will read in the supplied file Lab5SilverTest.java which contains a Java program, but with randomized indentation. Your program should fix the indentation as described below, and write out a new version of this file named Lab5SilverOutput.java. (These names are predefined for you as global constants.) To fix the indentation, do the following things:
    a. Remove any existing blanks from the front of each line. The built-in String method with the signature String trim() can be used to do this easily. It will remove all leading and trailing white space from any String. For example,

"    test one    ".trim()    will give the result    "test one"

    b. Add blanks to the front of each line to indent it properly. The amount of indentation should be 0 for the first line. Note the supplied String blanks(int n) method which will give you a String containing n blanks.

    c. If any line contains a "{" character, then increase the indentation for all following lines (but not this one) by an extra INDENT_AMOUNT blanks. This is a predefined constant. Note that the String method boolean contains(String) will tell you whether or not one String is contained inside another. For example, "Test".contains("e") will return
true.

    d. If any line contains a "}" character, then decrease the indentation for this line, and all following lines, by INDENT_AMOUNT.

    e. This makes the assumptions that { } braces are the only reason to ever indent a line in a Java program (which is not true), that no line will ever contain more than one brace character (also not necessarily true), and that the braces are properly matched up. But it will do a reasonable job of any file for which these assumptions are true.

For example, if the input file contained:

while(x){
doThis();
if(y){
doThat();
}//if

}//while

Then the output file should contain:

while(x){
doThis();
if(y){
doThat();

}//if
}//while



Exceptional Exceptions




In this exercise, you will use Exceptions to complete a program, including throwing an Exception from the catch block that is handling a previous exception. Begin with the supplied file TemplateLab5Gold.java. The static variables intArray and numElements form a standard partially-full array of integers. The insertIntoArray method adds a new integer to this list. It does no error checking and will throw an ArrayIndexOutOfBoundsException when the array is full. Do not modify this method in any way. The expandArray method will double the capacity of intArray. Add the following exceptions and exception handling to this program:

    1. Modify the addElement method (which, at the moment, simply calls the insertIntoArray method) so that it will catch the ArrayIndexOutOfBoundsException thrown by
insertIntoArray. When it does, it should print "Expanding the array", call expandArray

and then call insertIntoArray again, now that there is more room. Now everything should work. The main program will add the numbers 1-20 with no problem.

    2. But it has been decided that the array should never be allowed to become any larger than MAX_SIZE (predefined for you as 16). Modify the expandArray method so that it will not expand the array any more after it reaches this size. Instead, it should throw a
RuntimeException containing the message "Array at maximum capacity".

    3. You will now have to catch the RuntimeException in the addElement method. Note that the place that the exception will occur is inside the catch block from part 1. The addElement method should respond by printing out "Error in addElement: " followed by the message contained in the Exception. It should then throw a RuntimeException itself, containing the

message "Element xxx not added.".

    4. Catch this RuntimeException in the main program, where it should print the message "Error in main: " followed by the message in the exception.

    5. When working correctly, the output produced by the program should be:

element 1 added
element 2 added
Expanding the array

element 3 added
element 4 added
Expanding the array

element 5 added
element 6 added
element 7 added

element 8 added
Expanding the array
element 9 added
element 10 added

element 11 added
element 12 added
element 13 added

element 14 added
element 15 added
element 16 added

Expanding the array
Error in addElement: Array at maximum capacity
Error in main: Element 17 not added.