Java Programming Assignment 03

CSC 3020
Java Programming
Assignment 03
50 points


Assignment Objectives:
■■ To demonstrate how to define classes and create objects.
■■ To use UML graphical notation to describe classes and objects.
■■ To distinguish between object reference variables and primitive-datatype variables.
■■ To distinguish between instance and static variables and methods.
■■ To define private data fields with appropriate getter and setter methods.
■■ To create immutable objects from immutable classes to protect the contents of objects.
■■ To use the keyword this to refer to the calling object itself.








Solution to this assignment will not be posted on Canvas; however, any question can be discussed in the class upon request of a student.

All assignments must be submitted by the Canvas. No email or hard copy is accepted. You must follow the following format:
a.    For non-programming questions, use a word file to type your answers. Don’t use the text box on the Canvas to answer the questions or to write comments, we will not read it. 
b.    State your answer clearly.
c.    For programming questions, include only the source file for each problem.
d.    Submit your file to the Canvas. You must submit your assignment on time; otherwise, you will receive zero. In addition, you cannot submit your file more than one time. 
e.    There will be several folders on the Canvas. You need to upload your file(s) using the correct folder on the Canvas.
f.    Name each file:  “Assignment Number(Question number(s))”.
g.    To upload your file(s):
•    In Course Navigation, click the Assignments link.
•    Click the title of the assignment.
•    Click the Submit Assignment button.
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Make sure you review the Cheating & Plagiarism policy on Canvas.













Answer questions 1 to 3 on a word file; write a program for each of Q.4 - Q.7.

Q01. (10 points - 1 point each) 

1)    When will a class have a default constructor?
A class will have a default constructor only if no constructors are explicitly defined in the class.
2)    What is an anonymous object? 
An anonymous object is an object that is only used once and has no reference.
3)    What is NullPointerException?
A runtime error that occurs when invoking a method on a reference variable that has a null value.

4)    What is wrong in the following code?
 1  class Test {
 2    public static void main(String[] args) {
 3      A a = new A();
 4      a.print();
 5    }
 6  }
 7
 8  class A {
 9    String s;
10
11    A(String newS) {
12      s = newS;
13    }
14
15    public void print() {
16      System.out.print(s);
17    }
18  }

On line 3 no string is being placed into the object. Which means line 11 will not be called and it can not print anything.
5)    What is the output of the following code?
public class A {
  boolean x;
 
  public static void main(String[] args) {
    A a = new A();
    System.out.println(a.x);
  }
}
The output of the code will be false as the default value of the boolean is false.
6)     a. Can you invoke an instance method or use an instance variable from a static method? 
No because, static methods cannot invoke or access instance methods or data fields.
b. Can you invoke a static method or use a static variable from an instance method? 
Yes, static methods and variables can be invoked/accessed from an instance method.
7)    In the following code, radius is private in the Circle class, and myCircle is an object of the Circle class. Does the code cause any problems? If so, explain why.
public class Circle {
  private double radius = 1;

  /** Find the area of this circle */
  public double getArea() {
    return radius * radius * Math.PI;
  }

  public static void main(String[] args) {
    Circle myCircle = new Circle();
    System.out.println("Radius is " + myCircle.radius);
  }
}
No because private variables can still be accessed from within the same class.
8)     Describe the difference between passing a parameter of a primitive type and passing a parameter of a reference type. Show the output of the following programs:
public class Test {
  public static void main(String[] args) {
    Count myCount = new Count();
    int times = 0;

    for (int i = 0; i < 100; i++)
      increment(myCount, times);

    System.out.println("count is " + myCount.count);
    System.out.println("times is " + times);
  }

  public static void increment(Count c, int times) {
    c.count++;
    times++;
  }
}

class Count {
  public int count;

  public Count(int c) {
    count = c;
  }

  public Count() {
    count = 1;
  }
}
Passing a parameter of a primitive type involves the passing of the value to the parameter. Passing a parameter of a reference type passes a reference to the value.
Output:
    count is 101
    times is 0
9)     Is the following class immutable?
public class A {
  private int[] values;

  public int[] getValues() {
    return values;
  }
}
Yes, because all data fields are private their are no mutator methods and their are no accessor methods that return a reference to a mutable object.
10)     What is wrong in the following code? Corrected.
 1  public class C {
 2    private int p;
 3
 4    public C() {
 5      System.out.println("C's no-arg constructor 
                    invoked");
 6      this(0);
 7    }
 8
 9    public C(int p) {
10      p = p;
11    }
12
13    public void setP(int p) {
14      p = p;
15    }
16  }
The statement this(0); on line 6 must be first in the constructor.
Q02. (4 points) 
Suppose that the class F is defined in (a). Let f be an instance of F. 
Which of the statements in (b) are correct?
(a)
public class F {
  int i;
  static String s;

  void imethod() {
  }

  static void smethod() {
  }
}

(b)
System.out.println(f.i); Correct 
System.out.println(f.s); Correct
f.imethod(); Correct
f.smethod(); Correct
System.out.println(F.i);
System.out.println(F.s); Correct
F.imethod();
F.smethod(); Correct

Instance methods cannot be accessed without a reference variable.



Q03. (4 points) 
Show the output of the following code:
(a)
public class Test {
  public static void main(String[] args) {
    int[] a = {1, 2};
    swap(a[0], a[1]);
    System.out.println("a[1] = " + a[1] 
      + " a[0] = " + a[0]);    
  }

  public static void swap(int n1, int n2) {
    int temp = n1;
    n1 = n2;
    n2 = temp;
  }
} 
Output: a[1] = 2 a[0] = 1
(b)
public class Test {
  public static void main(String[] args) {
    int[] a = {1, 2};
    swap(a);
    System.out.println("a[1] = " + a[1] 
      + " a[0] = " + a[0]);    
  }

  public static void swap(int[] a) {
    int temp = a[0];
    a[0] = a[1];
    a[1] = temp;
  }
}
Output: a[1] = 1 a[0] = 2
(c)
public class Test {
  public static void main(String[] args) {
    T t = new T();
    swap(t);
    System.out.println("e1 = " + t.e1 
       + " e2 = " + t.e2);    
  }

  public static void swap(T t) {
    int temp = t.e1;
    t.e1 = t.e2;
    t.e2 = temp;
  }
}

class T {
  int e1 = 1;
  int e2 = 2; 
}
e1 = 2 e2 = 1
(d)
public class Test {
  public static void main(String[] args) {
    T t1 = new T(); 
    T t2 = new T(); 
    System.out.println("t1's i = " + 
      t1.i + " and j = " + t1.j);
    System.out.println("t2's i = " + 
      t2.i + " and j = " + t2.j);
  }  
}

class T {
  static int i = 1;
  int j = 1;

  T() {
    i++;
    j = 1;
  }
}            
t1’s i = 3 and j = 1
t2’s i = 3 and j = 1
Programming Questions
Q04. (8 points) 
In an n-sided regular polygon, all sides have the same length and all angles have the same degree. Design a class named RegularPolygon that contains:
•    A private int data field named n that defines the number of sides in the polygon with default value 3.
•    A private double data field named side that stores the length of the side with default value 1.
•    A private double data field named x that defines the x-coordinate of the polygon’s center with default value 0.
•    A private double data field named y that defines the y-coordinate of the polygon’s center with default value 0.
•    A no-arg constructor that creates a regular polygon with default values.
•    A constructor that creates a regular polygon with the specified number of sides and length of side, centered at (0, 0).
•    A constructor that creates a regular polygon with the specified number of sides, length of side, and x- and y-coordinates.
•    The accessor and mutator methods for all data fields.
•    The method getPerimeter() that returns the perimeter of the polygon.
•    The method getArea() that returns the area of the polygon. The formula for computing the area of a regular polygon is
  
.
Draw the UML diagram for the class then implement the class. Write a test program that creates three RegularPolygon objects, created using the no-arg constructor, using RegularPolygon(6, 4), and using RegularPolygon(10, 4, 5.6, 7.8). For each object, display its perimeter and area.

RegularPolygon
n: int
side: double
x: double
y: double
RegularPolygon()
RegularPolygon(numSides: int, sideLength: double)
RegularPolygon(numSides: int, sideLength: double, xCord: double, yCord:double)
setN(numSides: int): void
setSide(sideLength: double): void
setX(xCord: double): void
setY(yCord: double): void
getN(): int
getSide(): double
getX(): double
getY(): double
getPerimeter(pObj: RegularPolygon): double
getArea(aObj: RegularPolygon): double

Q05. (8 points)
Design a class named Time. The class contains:
•    The data fields hour, minute, and second that represent a time.
•    A no-arg constructor that creates a Time object for the current time. (The values of the data fields will represent the current time.)
•    A constructor that constructs a Time object with a specified elapsed time since midnight, January 1, 1970, in milliseconds. (The values of the data fields will represent this time.)
•    A constructor that constructs a Time object with the specified hour, minute, and second.
•    Three getter methods for the data fields hour, minute, and second, respectively.
•    A method named setTime(long elapseTime) that sets a new time for the object using the elapsed time. For example, if the elapsed time is 555550000 milliseconds, the hour is 10, the minute is 19, and the second is 10.

Draw the UML diagram for the class then implement the class. Write a test program that creates three Time objects (using new Time(), new Time(555550000), and new Time(5, 23, 55)) and displays their hour, minute, and second in the format hour:minute:second.

(Hint: The first two constructors will extract the hour, minute, and second from the elapsed time. For the no-arg constructor, the current time can be obtained using System.currentTimeMillis().
The currentTimeMillis method in the System class returns the current time in milliseconds elapsed since the time midnight, January 1, 1970 GMT (Assume the time is in GMT) .
Time
hour: long
minute: long
seconds: long
Time()
Time(time: long)
Time(h: long, m:long, s:long)
getHour(): long
getMinute(): long
getSeconds(): long
setTime(elapseTime: long): void

Q06. (8 points)
Design a class named MyInteger. The class contains:
•    An int data field named value that stores the int value represented by this object.
•    A constructor that creates a MyInteger object for the specified int value.
•    A getter method that returns the int value.
•    The methods isEven(), isOdd(), and isPrime() that return true if the value in this object is even, odd, or prime, respectively.
•    The static methods isEven(int), isOdd(int), and isPrime(int) that return true if the specified value is even, odd, or prime, respectively.
•    The static methods isEven(MyInteger), isOdd(MyInteger), and isPrime(MyInteger) that return true if the specified value is even, odd, or prime, respectively.
•    The methods equals(int) and equals(MyInteger) that return true if the value in this object is equal to the specified value.
•    A static method parseInt(char[]) that converts an array of numeric characters to an int value.
•    A static method parseInt(String) that converts a string into an int value.

Draw the UML diagram for the class then implement the class. Write a client
program that tests all methods in the class.
MyInteger
value: int
MyInteger(v: int):
getValue(): int
isEven(): boolean
isOdd(): boolean
isPrime(): boolean
isEven(v: int): static boolean
isOdd(v: int): static boolean
isPrime(v: int): static boolean
isEven(eObj: MyInteger): static boolean
isOdd(oObj: MyInteger): static boolean
isPrime(pObj: MyInteger): static boolean
equals(v: int): boolean
equals(eqObj: MyInteger): boolean
parseInt(arr: char[]): static int
parseInt(Str: String): static int

Q 07. (8 points)
Design a class named Queue for storing integers. Like a stack, a queue holds elements. In a stack, the elements are retrieved in a last-in first-out fashion. In a queue, the elements are
retrieved in a first-in first-out fashion. The class contains:
•    An int[] data field named elements that stores the int values in the queue.
•    A data field named size that stores the number of elements in the queue.
•    A constructor that creates a Queue object with default capacity 8.
•    The method enqueue(int v) that adds v into the queue.
•    The method dequeue() that removes and returns the element from the queue.
•    The method empty() that returns true if the queue is empty.
•    The method getSize() that returns the size of the queue.

Implement the class with the initial array size set to 8. The array size will be doubled once the number of the elements exceeds the size. After an element is removed from the beginning of the array, you need to shift all elements in the array one position the left. 
Write a test program that adds 20 numbers from 1 to 20 into the queue then removes these
numbers and displays them.