Spring Semester 2003

Let's go through a set of examples to clarify object-oriented concepts even further.

1. What's this program doing?

   Can you draw a diagram to illustrate what happens when you run it?

   public class One {
       public static void main(String[] args) {
   	Potato p = new Potato(); 
   	Potato q;
   	q = new Potato(); 
   	p = q;  
       } 
   } 
   
   class Potato {
   
   }

   How do the Potatoes get created?

2. What is this next program doing?

   Can you diagram it? What's new?

   public class Two {
       public static void main(String[] args) {
   	Pair u = new Pair(); 
   	Pair v;
   	v = new Pair(); 
           u.a = 1;
           u.b = 2;
           u.a = u.a + u.b; 
           u.b = 1 - u.a; 
       } 
   } 
   
   class Pair {
       int a;
       int b;
   } 

3. Why does this next program not compile?

   What's wrong with it?

   public class Three {
       public static void main(String[] args) {
   	Pair u = new Pair(); 
   	Pair v = new Pair(1, 2); 
       }
   } 
   
   class Pair {
       int a;
       int b; 
   } 

   Can you fix it?

4. What does the next program print and why (or how).

   public class Four {
       public static void main(String[] args) {
   	Calculator m = new Calculator(); 
   	int value = m.fun(3); 
   	System.out.println(value); 
       } 
   } 
   
   class Calculator {
       int fun(int x) {
   	int result;
           result = 3 * x + 1; 
           return result; 
       } 
   } 

   Same question if we change the Calculator as follows:

   class Calculator {
       int fun(int x) {
   	int result;
           result = g(x) + 1; 
           return result; 
       } 
       int g(int x) {
           int result;
           result = 3 * x; 
           return result; 
       }
   } 

5. What does the following program print and why (or how)?

   public class Five {
       public static void main(String[] args) {
   	Calculator c = new Calculator(); 
   	int value = c.fun(1) + c.fun(c.fun(2)); 
   	System.out.println(value); 
       } 
   } 
   
   class Calculator {
       int fun(int x) {
   	int result;
           result = 3 * x + 1; 
           return result; 
       } 
   }

6. Same question about this one:

   public class Six {
       public static void main(String[] args) {
   	Calculator calc = new Calculator(); 
   	int value = calc.fun(
                         calc.fun(
                           calc.fun(
                             calc.fun(
                               calc.fun(5)))));  
   	System.out.println(value); 
       } 
   }
   
   class Calculator {
       int fun(int x) {
   	int result;
           if (x % 2 == 0) 
             result = x / 2; 
           else 
             result = 3 * x + 1; 
           return result; 
       } 
   } 

7. What's the output of the following program and why?

   public class Seven {
       public static void main(String[] args) {
   	Oracle a = new Oracle(); 
   	System.out.println(a.odd(5));
   	System.out.println(a.odd(6));
   	System.out.println(a.odd(7));
   	System.out.println(a.odd(8));
   	System.out.println(a.odd(9));
       } 
   } 
   
   class Oracle {
       boolean odd(int n) {
   	boolean result; 
   	if (n % 2 == 0) {
   	    result = false; 
   	} else {
   	    result = true; 
   	} 
   	return result; 
       }
   }

8. Let's now review a previous step once again.

   What's the output of this program and why (or how)?

   public class Eight {
       public static void main(String[] args) {
           Calculator calc = new Calculator(); 
           int value = calc.fun(
                         calc.fun(
                           calc.fun(
                             calc.fun(
                               calc.fun(27)))));  
           System.out.println(value); 
       } 
   }
                 
   class Calculator {
       int fun(int x) {
           int result;
           if (x % 2 == 0) 
             result = x / 2; 
           else 
             result = 3 * x + 1; 
           return result; 
       } 
   } 

9. Now fasten your seat belts and look closely.

   What's the output of this program and why (or how)?

   public class Nine {
       public static void main(String[] args) {
   	Alien x = new Alien(); 
   	int value = x.what(4); 
   	System.out.println(value); 
       } 
   }
   
   class Alien {
       int what(int x) {
   	int result;
   	if (x == 1) { 
   	    result = 1;
   	} else {
   	    result = x + what(x - 1);
   	}
           return result; 
       } 
   } 

10. What's a good name for the method what?

11. What's the output of this program?

    public class Eleven {
        public static void main(String[] args) {
    	Alien x = new Alien(); 
    	int value = x.what(10); 
    	System.out.println(value); 
        } 
    }
    
    class Alien {
        int what(int x) {
    	int result;
    	if (x == 1) { 
    	    result = 1;
    	} else {
    	    result = x + what(x - 1);
    	}
            return result; 
        } 
    }

12. What's the output of this program and why (or how)?

    public class Twelve {
        public static void main(String[] args) {
    	Alien x = new Alien(); 
    	int value = x.what(10); 
    	System.out.println(value); 
        } 
    }
    
    class Alien {
        int what(int x) {
    	int result;
    	if (x == 1) { 
    	    result = 1;
    	} else {
                System.out.println(x); 
    	    result = x + what(x - 1);
    	}
            return result; 
        } 
    } 

13. What's the output of this program and why (or how)?

    public class Thirteen {
        public static void main(String[] args) {
    	Alien x = new Alien(); 
    	int value = x.what(10); 
    	System.out.println(value); 
        } 
    }
    
    class Alien {
        int what(int x) {
    	int result;
    	if (x == 1) { 
    	    result = 1;
    	} else {
    	    result = x + what(x - 1);
                System.out.println(x); 
    	}
            return result; 
        } 
    } 

14. What's the output of this program and why?

    public class Fourteen {
        public static void main(String[] args) {
    	A a = new A();
    	a.fun();
    	a.fun();
    	a.fun();
    	System.out.println(a.n);
        }
    }
    
    class A {
        int n;
        void fun() {
    	n += 1;
        }
    }

15. What's the output of this program and why?

    public class Fifteen {
        public static void main(String[] args) {
    	Vegetable tomato = new Vegetable();
    	tomato.f(); 
    	tomato.f(); 
    	tomato.g(); 
    	System.out.println(tomato.n); 
    	tomato.g();
    	tomato.g(); 
    	tomato.f(); 
    	System.out.println(tomato.n); 
        }
    }
    
    class Vegetable {
        int n;
        void f() {
    	n = n + 1;
        }
        void g() {
            n = n + 1; 
        } 
    
    }

16. What is the output of this program and why?

    public class Sixteen {
        public static void main(String[] args) {
    	Vegetable tomato = new Vegetable();
    	Vegetable potato = new Vegetable();
    	tomato.fun();
    	tomato.fun();
    	potato.fun(); 
    	tomato.fun();
    	potato.fun();
    	potato.fun();
    	potato.fun();
    	tomato.fun();
        } 
    }
    
    class Vegetable {
        int n;
        int m;
        void fun() {
    	n = n + 1;
    	m = m + 1;
    	System.out.println("n = " + n + ", m = " + m);
        }
    }

17. What is the output of this program and why?

    public class Seventeen {
        public static void main(String[] args) {
    	Vegetable tomato = new Vegetable();
    	Vegetable potato = new Vegetable();
    	tomato.fun();
    	tomato.fun();
    	potato.fun(); 
    	tomato.fun();
    	potato.fun();
    	potato.fun();
    	potato.fun();
    	tomato.fun();
        } 
    }
    
    class Vegetable {
        int n;
        static int m;
        void fun() {
    	n = n + 1;
    	m = m + 1;
    	System.out.println("n = " + n + ", m = " + m);
        }
    }

18. Please describe briefly what this picture represents:

    

    Define all terms involved, as briefly and completely as you can.

19. Take a look at the diagram below:

    

    Then please answer the following question:

    What's this?

20. More generally the picture looks like this:

    

    Can you summarize the diagram briefly?

What comes next is your:

A201/A597 LAB ASSIGNMENT FIVE

• answer all 20 questions
• on a piece of paper (one sheet front and back)
• as succinctly yet as completely and legibly as possible,
• then bring it with you to lab next time (Feb 20-21)

In lab, the AI will

• come to you (for grading)
• will request the paper with the answers
• and after briefly reviewing it
• will ask you a question (or two)

In your papers try to give honest, direct answers.

In addition, please explain why this doesn't work. Then fix it in two different ways.

public class Math {
  public static void main(String[] args) {
    int a = 5;
    int b = 7; 
    System.out.println(Math.max(a, b)); 
  }
}

If you have any questions or need any help please let us know!