CSC212 Lab 4 2014

--D. Thiebaut (talk) 21:12, 17 September 2014 (EDT)

---

Lab 4 deals with private member variables, and javadoc.

Private Member Variables

• Login to beowulf2.csc.smith.edu, grendel.csc.smith.edu, or use one of the Linux Mint machines.
• Create a new program called Animal1.java containing the code below:

public class Animal1 {
        boolean isVaccinated;
        boolean isTattooed;
        String name;
        int age;
        
        Animal1( String n, int a, boolean v, boolean t ) {
                name             = n;
                age              = a;
                isVaccinated = v;
                isTattooed   = t;
        }
        
        public void displayBasicInfo( ) {
                String v = "vaccinated";
                if ( !isVaccinated ) v = "not " + v;
                String t = "tattooed";
                if ( !isTattooed ) t = "not " + t;
                System.out.println( String.format( "%s (%d), %s, %s", 
                                name, age, t, v ) );
        }
        
}

• In the same directory, create a second file called TestAnimal1.java, which contains this code:

class TestAnimal1 {

   TestAnimal1() { 
   }

   public static void main(String[] args) {
           // create a new animal
           Animal1 a = new Animal1( "Max", 3, false, true );
           a.displayBasicInfo();

           // modify it.  Then display it.
           a.isVaccinated = true;
           a.isTattooed = false;
           a.age = 5;
           a.displayBasicInfo();

           // modify it some more, then display it.
           a.isTattooed = ! a.isTattooed;
           a.age = a.age + 1;
           a.displayBasicInfo();
   }
}

• Compile and run both:

 javac Animal1.java TestAnimal1.java
 java TestAnimal1

• Verify that you get the following output:

Max (3), tattooed, not vaccinated
Max (5), not tattooed, vaccinated
Max (6), tattooed, vaccinated

Modification

• Modify the Animal1.java program and make all its member variables private.

        private boolean isVaccinated;
        private boolean isTattooed;
        private String name;
        private int age;

• Recompile both java programs. Notice that, now, TestAnimal1.java generates many errors. Why?
• If you answer that it is because TestAnimal1 cannot access the member variables of a any longer, you are right!
• Modify both Animal1 and TestAnimal1 so that

• Animal1 will now have mutator and inspector methods to access its member functions, and
• TestAnimal1 will access the member variables of a by using the new accessors and mutators

• Here is an example of a modification you can make on Animal1.java

         // mutator
         public void setAge( int n ) {
               age = n;
         }

         // ispector
         public int getAge( ) {
               return age;
         }

• And here is an example of a modification you can make on TestAnimal1.java:

        a.setAge( 5 );

• When you have been able to get rid of all the compiler errors for TestAnimal1.java, run the program TestAnimal1 and verify that you get the same output as before:

Max (3), tattooed, not vaccinated
Max (5), not tattooed, vaccinated
Max (6), tattooed, vaccinated