Objectives:

• Read from and write to files using simpleIO (using the SimpleReader and SimpleWriter classes).
• Handle relevant exceptions.
• Learn to test for end-of-file conditions on input.
• Implement the selection sort.
• Implement the binary search.

In this laboratory, you will be using the SimpleReader and SimpleWriter classes that are described in Section 7.8 of the textbook to input and output arrays. These classes are part of the simpleIO package. In part II you will be adding a selection sort similar to the version given in lecture or on page 334 of the textbook. In part III you will be added a binary search as covered in lecture.

Check-off procedure:

You must attend the recitation and sign in. This laboratory will be checked off using the new procedures.

Laboratory details:

Part I: Array Input and Output

In this part of the laboratory you will begin the implementation of a class called SortedArray and a main test program.

• Create a standalone project called SortedArrayMain.
• Create a new file called SortedArray.java and add it to the project.
• The SortedArray.java contains the class definition of SortedArray:
  • The SortedArray has one field: myArray which is an array of integers.

  • The SortedArray class has a constructor of the form:

       public SortedArray(String filename, int size) {
    
       }
    

    where filename is the name of the file that the values of the array are to be read from. The size parameter indicates the length of the array.

  • The constructor should call a private initialize(String filename, int size) method that handles the creation of the array and the reading of its values in from the file. The initialize method should also handle the opening and closing of the file. It should catch the FileNotFoundException and the IOException. If there are fewer items in the file than size, fill in the remaining entries of myArray with zeroes. (For this part, the detection of not having enough elements will be caught as an IOException.)

  • The SortedArray has a public method:

        public boolean write(String filename) {
    
        }
    

    This method writes myArray to the file named filename. The method handles the opening and closing of the file by using SimpleWriter. It should catch the FileNotFoundException and the IOException. If an exception occurs, the method returns false otherwise the method returns true.

  • You will need to import the simpleIO and java.io packages in SortedArray:

    import simpleIO.*;
    import java.io.*;
    

  • Write code in the main test program to instantiate SortedArray objects generated from a valid file with enough values, a non-existent file, and a file with too few values. (You can check the output files by bringing them into the MS Notepad which can be found on the Accessories menu of Start.) The tests assume that you are in the teaching lab and have mapped \\colab2\classes to your X: drive.
    • Test I: Instantiate a SortedArray to read an array of 5 elements from the file X:\1711\lab11test1.dat. This file has 11 elements in it and should work successfully.
    • Test II: Instantiate a SortedArray to read an array of 11 elements from the file X:\1711\lab11test1NotHere.dat. There is no file with this name and it should give an exception. Change the name to X:\1711\lab11test1.dat and try again.
    • Test III: Instantiate a SortedArray to read an array of 20 elements from the file X:\1711\lab11test1.dat. There are only 11 values in this file so this should generate an exception. Change the number of elements in the array to 10 and try again.

  • When you specify the files, you will have to give the complete pathname and specify the \ as a \\ in the pathname. The TA will give you the name of some files that will be used for testing.

  Part II: Adding EOFtest

  • Modify initialize to test for end of file by calling the EOF method of SimpleReader.
  • Test this modification using Test III of Part I. Notice that you do not generate an IOException this time.

  Part III: Selection Sort

  • Add a private helper function called sort to the SortedArray class to sort myArray in ascending order. Use the selection sort algorithm as discussed in the lecture and on page 334 of the textbook.
  • Call this helper function from initialize so that myArray holds a sorted version of the inputted array.
  • Test to make sure the program works.

  Part IV: Binary Search

  • Add a public method called find that has the following form:

        public int find(int value) {
    
        }
    

    The find returns the position of value in myArray or -1 if it isn't there. Use the binary search algorithm developed during the lecture to find the value.

  • Build and add test code.

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  Last revision: November 18, 1999 at 10:40 am