To Lecture Notes

IT 313 -- Jan 23, 2020

Review Exercises

1. What is the output?
   

   System.out.println('R' + 91);
   System.out.println("" + 'R' + 91);
   
   Ans:
   173
   R91
   

   For char + int, both values are treated as numeric, so the char is changed to its ASCII(or Unicode) code.
For String + char + int, String + char is performed first, which is a String, then String + remaining_int is also String.
2. Add the static variable numObjects to your Counter class from Monday.
   Ans: add this code to your Counter class:
   

   private static numObjects = 0;
   
   public int getNumObjects( ) {
       return numObjects;
   }
   

   Add this line to your Counter constructor:
   

   numObjects++;
   

3. Look at the unicode1 and unicode2 modules in the Unicode Example project.
4. For Project 3 test these instance variables:
         getAmtForPurchase   depositDime   purchaseCandyBar
   Provide traditional and unit tests. Ans:
   

   // Traditional Test File: Test1.java
   // Stan Smith
   // Project 3
   // Jan 23, 2020
   
   public class Test1 {
       public static void main(String[] args) {
   
           // Write and test these two lines before
           // typing anything else into your test file.
           VendingMachine vm = new VendingMachine();
           System.out.println(vm);
   
           // Test depositDime, getAmtForPurchase, and
           // purchaseCandyBar
           vm.depositDime( );
           vm.depositDime( );
           vm.depositDime( );
           vm.depositNickel( );
           vm.depositQuarter( );
           vm.depositQuarter( );
           System.out.println(vm.getAmtForPurchase( ));
           vm.loadCandyBars(5);
           vm.purchaseCandyBar( );
           System.out.println(vm);
       }
   }
           
   
   
   / Unit test file: Test2.java
   import org.junit.jupiter.api.BeforeEach;
   import org.junit.jupiter.api.Test;
   import static org.junit.jupiter.api.Assertions.*;
   
   class Test2 {
       private VendingMachine vm;
   
       @BeforeEach
       void setUp() {
           vm = new VendingMachine( );
           vm.loadCandyBars(5);
       }
   
       @Test
       void testAmtForPurchase( ) {
           assertEquals(0, vm.getAmtForPurchase( ));
       }
   
       @Test
       void testDepositDime() {
           vm.depositDime( );
           assertEquals(10, vm.getAmtForPurchase( ));
       }
   
       @Test
       public void testPurchaseCandyBar() {
           for(int i = 1; i <= 3; i++) {
               vm.depositQuarter( );
           }
           vm.purchaseCandyBar();
           assertEquals(vm.toString( ),"4 0 Candy bar dispensed");
       }
   }
   

The StringBuilder Class

• Look at the ssbcompare module in the InstanceMethods Example.

File I/O

• Write a program that reads a name from the input file name.txt, then prints a greeting to the output file greeting.txt. To write to an output file:
  

  /* Before class header: */
  import java.io.*;
  
  /* The main method: */
  public static void main(String[ ] args) 
      throws FileNotFoundException {
  
      PrintWriter pw = new PrintWriter("greeting.txt");
      pw.println("Hello.");
      pw.close( );
  }
  

  greeting.txt is created in the project folder, not in the src or bin folders.
• Write a program to read names from the input file names.txt, then prints a greeting to one output file per name. For example, if names.txt contains
  

  Alice
  Peter
  

  The greeting should be written to the files alice.txt and peter.txt.
  Ans: See the WriteGreetings class in the InputOutput Example project.
• Modify question 3 to use a file dialog to obtain the name of the input file. Look up the JFileChooser class in the Java Class Library.
  Ans: See the UseFileChooser class in InputOutput Example project.