CS 12300 Final Exam Review

The final exam is on Thursday, December 17.

The final exam is over the whole semester.

Be sure to review the review problems for each of the first
two midterm exams and also review the two exams themselves.

The sections covered since the second midterm exam are 
Chapters 7, 9, 10 and 11 from Think Java, and the following 
sections from https://runestone.academy/runestone/books/published/csjava/index.html
   Sections 6.1, 6.2, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9.
   Sections 7.1, 7.2.


The topics covered since the second midterm exam are:
   1) arrays,
      array reference variables,
      array objects,
      array initialization,
      aliases,
      array parameters to methods,
      array return value from methods.
   2) classes,
      instance variables (fields)
      instance methods (instead of static methods),
      constructors,
      this keyword,
      dot notation,
      accessor methods,
      variable scope,
      equals() vs. ==,
      mutable vs. immutable objects.


Below are review problems for the material we have covered
since the second midterm exam. For the final exam you should 
also study Exam 1 and Exam 2 plus the review problems for 
those two exams.



Problem 1) If variable a is a reference to an array, what happens if the
following statement is executed? Briefly explain why.

    System.out.println(a[a.length]);


Problem 2) Assume that A is a reference to an array containing integers. 
Write a for-loop that multiplies every element in A by 10.


Problem 3) Write a program segment that declares an array reference variable, 
constructs an array object, assigns the array object to the array variable, 
and then uses a loop to fill the array object with the following integers.

   -50, -40, -30, -20, -10, 0, 10, 20, 30, 40, 50.


Problem 4) Write a method called sumArray that accepts a reference to an array
of doubles and returns the sum of the values stored in the array.


Problem 5) Write a method called sumSubArray that accepts a reference to an 
array of doubles and two ints. If the two ints are valid indices, then the
method should return the sum of the values stored in the array whose indices
are between the two ints (inclusive). If the two ints are not valid indices,
then the method should return zero.


Problem 6) Suppose that the variables a and b are references to arrays of
integers with length at least two. What is the value of b[0] and b[1] after
the following statements have been executed? Explain why. Your explanation
should include a simple drawing of Java’s memory.

   a[0] = 1;
   b[0] = 2;
   b = a;
   b[1] = 3;
   a[1] = 4;


Problem 7) After the following code has executed its last line, 
how many array objects have reference variables referring to them?
Explain your answer with a drawing of Java's memory.

   int[] a = {21, 11, 10, 9};
   int[] b = new int[6];
   int[] c = a;
   a = new int[5];
   b = a;
   int[] d = b;
   

Problem 8) Show the output of the following program.
Explain what the second for-loop is doing.

   public class Problem
   {
      public static void main(String[] args)
      {
         int[] a = new int[8];
         for (int i = 0; i < a.length; i++)
         {
            a[i]=i+1;
            System.out.println(a[i]);
         }
         int result = 0;
         for (int i = 0; i < a.length / 2; i++)
         {
            result += a[i] * a[a.length-i-1];
         }
         System.out.println("Result = " + result);
      }
   }


Problem 9) Suppose that the parameter A is always a reference to 
an array of size n >= 2 containing integers from 1 to n-1, inclusive,
with exactly one number repeated. Write the method

   public static int findRepeatedNumber(int[] A)

that returns the value of the repeated number in the array A.
(Hint: Use two nested for-loops.)



Problem 10) Suppose I have defined a class called Thing. 
The following line performs three distinct steps. What 
are they? How would you rewrite this single line as two
lines? What distinct steps do each of those two lines perform?

   Thing rose = new Thing();



Problem 11) Consider the following class definition.

   class Thing
   {
      private int x;
      private double y;
      public void setX(int x) { this.x = x; }
      public void setY(double y) { this.y = y; }
      public int getX() { return x; }
      public double getY() { return y; }
      public int methodA() { return 2*x; }
      public double methodB() { return 3*y; }
   }


Suppose that we have the following declarations.

   Thing a = new Thing();
   Thing b = new Thing();

Explain why each of the following statements is either OK or not OK.

   b.x = 5;

   int u = a.getY();
   
   double v = b.getX();
   
   a.setX(3.2);
   
   b.getY();
   
   double w = b.setY(4.5);

   int x = Thing.methodA();

   int y = a.methodB(5);
   
   a = b.methodA();
   
   a = b;



Problem 12) There are several mistakes in the following class definition.
Explain what the mistakes are and show how to correct them.

/* 1*/   public class Liquid
/* 2*/   {
/* 3*/      private int currentTemperature;
/* 4*/
/* 5*/      public Liquid()
/* 6*/      {
/* 7*/         currentTemperature = ct;
/* 8*/      }
/* 9*/
/*10*/      public void getCurrentTemperature(int ct)
/*11*/      {
/*12*/         return ct;
/*13*/      }
/*14*/   
/*15*/      public void setCurrentTemperature(int ct)
/*16*/      {
/*17*/         currentTemperature + ct;
/*18*/      }
/*19*/   }


Problem 13) In the Liquid class below, the raiseTemperature() method is
intended to mutate the value of the instance variable currentTemp by
the value of the parameter increase. The method does not work as intended.
Explain what is wrong and show how to correct it.

/* 1*/   public class Liquid
/* 2*/   {
/* 3*/      private int currentTemp;
/* 4*/
/* 5*/      public Liquid(int ct)
/* 6*/      {
/* 7*/         currentTemp = ct;
/* 8*/      }
/* 9*/
/*10*/      public int raiseTemperature(int increase)
/*11*/      {
/*12*/         return currentTemp + increase;
/*13*/      }
/*14*/   }


Problem 14) In the following class, implement two boolean methods
isFrozen() and isBoiling().

public class Liquid
{
    private double freezingPoint;
    private double boilingPoint;
    private double currentTemp;

    public Liquid(double fp, double bp, double ct)
    {
        freezingPoint = fp;
        boilingPoint = bp;
        currentTemp = ct;
    }

    /* isBoiling() and isFrozen() methods */

}


Problem 15) Below is the outline of a simple class called BusyWork. 
In the blank space provided in the class, add two methods to the class. 
The two methods that you add can make use of the two given methods
setNumber() and getNumber().

(a) Add a method increment() that adds 1 to the value of m.


(b) Add a method decrement() that returns a BusyWork object whose
value of m is one less than the value stored in the called object.
This method should not modify the m in the object the method is called on.


   class BusyWork
   {
      int m = 0;

      public void setNumber(int m)
      {
         this.m = m;
      }

      public int getNumber()
      {
         return this.m;
      }

      // write the methods increment() and decrement()



   }//BusyWork