Question

The Date Class

This class will function similarly in spirit to the Date class in the text, and behaves very much like a “standard” class should. It should store a month, day, and year, in addition to providing useful functions like date reporting (toString()), date setting (constructors and getters/setters), as well as some basic error detection (for example, all month values should be between 1-12, if represented as an integer). Start this by defining a new class called “Date” or use Date.java, and implement the data items and methods listed in your “contract” below. By declaring both data and methods that will operate on this data in one file, we are “wrapping up” chunks of dedicated functionality (methods) with the data items that they operate on in one clean and simple abstraction: the Class. To test your Date class use the driver ClassDesignIIDriver.java. If you are starting from an existing Date.java, carefully read the instructions bellow to be sure that you have added all new functionality.

Class Invariants

Enforce the following “rules” that your class should never violate. By doing this you maintain the coherency of your object’s internal state – this is also known as “never invalidating the state (data) of your object”. In our Fractions homework, this would involve modifying getters/setters so as to never accept a zero denominator. Here we’ll consider some Invariants for the Date class.

• All month values should be in between 1-12
• All day values should be in between 1-31
• All year values should be positive.

Data Members

Declare a variable for month, day, and year.

• Define these as private? public?
  1. What is the difference between the public and private access modifiers?
  2. When data is defined as static...
     1. Can it be accessed or read?
     2. Can it be written to?
     3. If we had declared one static variable and 10 objects declared in RAM, how many static variables would also be in memory?
  3. When data is defined as final...
     1. Can it be accessed/used or read?
     2. Can it be written to other than the first initialization?
     3. Why would it be ok to declare a final (or static final) variable as public?
     4. Later: How does the concept of a final variable relate to Immutable classes?

Method Members

• Provide getter/setter methods for each of the variables above
• Provide logic in your setter methods to observe the following Class Invariants
• public Date() {}
  • This is the default no-arg constructor.
• public Date(int m, int d, int y);
  • Should we use month = m; or setMonth(m)? What are the differences?
• public Date(Date other);
  • This method is a copy constructor; initialize your object’s data members (this.month, etc) using “other”.
• public String toString(); //report on your date
• public boolean equals(Object other);
  • In this method, you’ll compare “this” to “that”, once the other object has been checked and cast.
  • See Fraction equals() for proper null-check and casting.

Sample Output

• a is :0.0.0
• b is :2.1.2030
• c is :2.1.2030
• B and A are equal: false
• B and C are equal: true

Answer 1

PLEASE GIVE IT A THUMBS UP, I SERIOUSLY NEED ONE, IF YOU NEED ANY MODIFICATION THEN LET ME KNOW, I WILL DO IT FOR YOU

Que- Define these as private? public?

Ans- Define these as private for acheaving encapsulation and data hiding and expose these variables only through getters and setters.

Que- What is difference between the public and private access modifiers?

Ans- private access modifier is accessible only within class

public access modifier is accessible everywhere means outside class also.

Que- When data is define as a static?

Ans- When we want to share particular data value with all objects then we can define data as a static.

Ex-If in a college there are 500 students and all are having same college name so in this case we can declare college

name as a static

class students

{

static String collegeName="abc";

int rollNo;

String studentName;

}

Que- a) can it be accessed or read?

Ans- Yes it can be accessed or read

Que- b)can it be written to?

Ans-Yes

Que-If we had decaler one static variable and 10 objects declare in RAM,how manny static variables would also be in a memory?

Ans-There will be only one satic variable which will be created at the time of class loading and common to all 10 objects.

Que-a) When data is define as a final.

Ans- Data can be define as a final when we dont want to modify its value after its first initialization and we want its constant value

throught program life cycle.

Que-b) Can it be written other than first initialization?

Ans- We can not change constant variable value once it initialized. If you are using blank final variable then you should initializ this variable in

constructor.

Que-c) Why would it be Ok to declare a final (or static final) variable as a public?

Ans- We can access it outside class also. It is final variable so no one can change its value so no need to keep it as a private.

Que- Later: How does the concept of a final variable relate to Immutable class?

Ans- When we need to prevent particular class from extending and when we dont want to change the attributes/variables values of particular class

at that time we should make the class immutable by using final keyword.

Que- Should we use month=m;or setMonth(m)? What are the differences?

Ans- In your case you are writing validation logic in setter method so we need to use setter method in constructor to validate fields.

but in normal case it will not be good practice to use setter method in constructor beacause one can override your methods and can change their behaiviour

class Date {
  private int day;

  private int month;

  private int year;

  // default constructor

  public Date() {
    this.day = 0;

    this.month = 0;

    this.year = 0;
  }

  // parameterize constructor

  public Date(int m, int d, int y) {
    setDay(d);

    setMonth(m);

    setYear(y);
  }

  //copy constructor

  public Date(Date other) {
    this.day = other.day;

    this.month = other.month;

    this.year = other.year;
  }

  // getters and setters

  public int getDay() {
    return day;
  }

  public void setDay(int day) {
    if (day >= 1 && day <= 31) this.day = day; else System.out.println(
      "Error: Day value should be between 1 to 31"
    );
  }

  public int getMonth() {
    return month;
  }

  public void setMonth(int month) {
    if (month >= 1 && month <= 12) this.month = month; else System.out.println(
      "Error: Month value should be between 1 to 12"
    );
  }

  public int getYear() {
    return year;
  }

  public void setYear(int year) {
    if (year >= 0) this.year = year; else System.out.println(
      "Error: Year value must have positive"
    );
  }

  @Override
  public String toString() {
    return month + "." + day + "." + year;
  }

  @Override
  public boolean equals(Object obj) {
    if (this == obj) return true;

    if (obj == null) return false;

    if (getClass() != obj.getClass()) return false;

    Date other = (Date) obj;

    if (day != other.day) return false;

    if (month != other.month) return false;

    if (year != other.year) return false;

    return true;
  }

  public static void main(String[] args) {
    Date a = new Date();

    Date b = new Date(2, 1, 2030);

    Date c = new Date(2, 1, 2030);

    System.out.println("a is : " + a.toString());

    System.out.println("b is : " + b.toString());

    System.out.println("b is : " + c.toString());

    System.out.println("B and A are equal : " + b.equals(a));

    System.out.println("B and C are equal : " + b.equals(c));
  }
}