Question

Learning Objectives

• Writing classes that represent objects
• Define object's state (Instance variables)
• Define objects constructors
• Write getter (accessor) and setter (mutator) methods.

As in previous labs, please write the Java code for each of the following exercises in BlueJ. For each exercise, write a comment before the code stating the exercise number.

Make sure you are using the appropriate indentation and styling conventions

Exercise 1 (15 Points)

• In BlueJ, create a new project called Lab5
• In the project create a class called DogDemo with a static method called makeDogs
• Create a second class in the same project called Dog that will represent a single dog (just a class header and an empty body for now).
• In the makeDogs method, create a Dog object called myDog. Note that the Dog and DogDemo classes are now connected by a dotted arrow in the project window to show that DogDemo depends on (uses) the Dog class.

Exercise 2 (20 Points)

• In the Dog class, create a variable at the class level (also called instance data or a field) that will represent the dog's name (a String).
• Declare this variable as private. This puts the Dog class in charge of how the name gets updated. This variable is not DIRECTLY accessible from outside the Dog class.
• In the declaration of the variable, initialize it to "Lassie".
• Create a toString method that returns the dog's name.
• In the makeDogs method of the DogDemo class, print the Dog object you created. Run the makeDogs method.

Exercise 3 (15 Points)

• This would be OK if all dogs were named Lassie!! Each instance of Dog (each Dog object) will have its own name variable, which contain different values. So create a constructor in the Dog class that accepts a parameter which is used to set the name variable.
• In the makeDogs method, create a new dog and pass in the name "Lassie" to its constructor.
• Create a second Dog object with a different name, "Rover" for example.
• Print the two dog objects.

Exercise 4 (15 Points)

• Add another field to the Dog class representing the dog's breed (a String) and one representing the dog's age (an int). Both fields should be private.
• Modify the Dog constructor to set these values as well, based on parameters.
• Define a new Dog objects in makeDogs and give them a name, breed and age.
• Modify the toString method to return a string in the following form:

Fido is a 3-year-old German Sheppard

• Test the updated makeDogs method. Think through what is happening at each step.

Exercise 5 (10 Points)

• Add standard "getter" methods for all three fields. Remember that getter methods just returns the value of a private instance variable (field). This will make the value of a private variable accessible ONLY through this method.
• In the makeDogs method, get and print just the breed of one of your created objects.
• Then get and print just the name of another one of the created objects.

Exercise 6 (10 Points)

• In Dog, add a "setter" method for the age field. Don't change the age if the parameter is less than 1.
• In the makeDogs method, try to set the age of yourDog to 0, then print the Dog object to make sure the age did not change.
• Then set the age of yourDog to 4 and print it again.

Exercise 7 (15 Points)

• You may have heard the expression "That's 21 in dog years" or something similar. The idea is to come up with a number to make it easy to compare a dog's age to that of a human in terms of overall life span. The calculation used is real age multiplied by 7. So a dog that's 3 years old is "21 in dog years".
• Add a method in Dog called getDogYears that returns the dog's age in dog-years. Do NOT create another field for this. Just return the dog's current age multiplied by 7.
• In the makeDogs method, print each dog's age in dog-years:

Rover is 28 in dog-years.

Answer 1

Here is the code for the given exercises, as each exercise is an enhancement of existing exercise, I mentioned the exercise number for each statement. Code separate by each exercise are pasted at the end

DogDemo.java

//Exercise-1 creating class DogDemo
public class DogDemo
{
    /**
     * Exercise-1 Static method called makeDogs
     */
    public static void makeDogs()
    {
        /*
        //Exercise-1 create a Dog object called myDog
        Dog myDog = new Dog();
        //Exercise-2 print the Dog object you created.
        System.out.println(myDog.toString());
        //Exercise-3 create a new dog and pass in the name "Lassie" to its constructor.
        Dog myDog1 = new Dog("Lassie");
        //Exercise-3 Create a second Dog object with a different name, "Rover" for example.
        Dog myDog2 = new Dog("Rover");
        //Exercise-3 Print the two dog objects.
        System.out.println(myDog1.toString());
        System.out.println(myDog2.toString());
        */
        //Exercise-4 Define a new Dog objects in makeDogs and give them a name, breed and age.
        Dog myDog3 = new Dog("Fido", "German Sheppard", 3);
        //Exercise-4 print the dog object
        System.out.println(myDog3.toString());
        //Exercise-5 get and print just the breed of one of your created objects.
        System.out.println(myDog3.getBreed());
        //Exercise-6 try to set the age of yourDog to 0
        myDog3.setAge(0);
        //Exercise-6 print the Dog object to make sure the age did not change.
        System.out.println(myDog3.getAge());
        //Exercise-6 set the age of yourDog to 4 and print it again.
        myDog3.setAge(4);
        System.out.println(myDog3.getAge());
        //Exercise-7 print each dog's age in dog-years:Rover is 28 in dog-years.
        System.out.println(myDog3.getName() + " is " + myDog3.getDogYears() + " in dog-years." );
    }
}

Dog.java

// Exercise-1 creating class Dog
public class Dog
{
    //Exercise-2 create a variable at the class level that will represent the dog's name (a String). Initialize it to Lassie
    private String name = "Lassie";
    //Exercise-4 Add another field to the Dog class representing the dog's breed (a String)
    private String breed;
    //Exercise-4 add another field representing the dog's age (an int).
    private int age;
  
    /**Exercise-2
     * toString method that returns the dog's name.
     */
    public String toString()
    {
        //return this.name;
        //Exercise4 Modify the toString method to return a string
        return this.name + " is a " + this.age + "-year-old " + this.breed;
    }
  
    /**Exercise-3
     * create a constructor in the Dog class that accepts a parameters which is used to set the variables.
     */
    public Dog(String dogName, String dogBreed, int dogAge)
    {
        this.name = dogName;
        //Exercise-4 Modify the Dog constructor to set these values as well, based on parameters.
        this.breed = dogBreed;
        this.age = dogAge;
    }
  
    /**Exercise-5
     * Create getter methods for all the three variables
     */
    public String getName()
    {
        return this.name;
    }
  
    public String getBreed()
    {
        return this.breed;
    }
  
    public int getAge()
    {
        return this.age;
    }
  
    /**Exercise-6
     * Add a "setter" method for the age field
     */
    public void setAge(int dogAge)
    {
        //Exercise-6 Don't change the age if the parameter is less than 1.
        if(dogAge >= 1)
            this.age = dogAge;
    }
  
    /**Exercise-7
     * Add a method in Dog called getDogYears that returns the dog's age in dog-years.
     */
    public int getDogYears()
    {
        return this.getAge() * 7;
    }
}

Output (Each line is the output generated for each exercise)

Below are the code for each exercise

Exercise-1
DogDemo.java
//Exercise-1 creating class DogDemo
public class DogDemo
{
    /**
     * Exercise-1 Static method called makeDogs
     */
    public static void makeDogs()
    {
        //Exercise-1 create a Dog object called myDog
        Dog myDog = new Dog();
    }
}

Dog.java
// Exercise-1 creating class Dog
public class Dog
{

}

Exercise-2
DogDemo.java
//Exercise-1 creating class DogDemo
public class DogDemo
{
    /**
     * Exercise-1 Static method called makeDogs
     */
    public static void makeDogs()
    {
        //Exercise-1 create a Dog object called myDog
        Dog myDog = new Dog();
        //Exercise-2 print the Dog object you created.
        System.out.println(myDog.toString());
    }
}

Dog.java
// Exercise-1 creating class Dog
public class Dog
{
    //Exercise-2 create a variable at the class level that will represent the dog's name (a String). Initialize it to Lassie
    private String name = "Lassie";
  
    /**Exercise-2
     * toString method that returns the dog's name.
     */
    public String toString()
    {
        return this.name;
    }
}

Exercise-3
DogDemo.java
//Exercise-1 creating class DogDemo
public class DogDemo
{
    /**
     * Exercise-1 Static method called makeDogs
     */
    public static void makeDogs()
    {
        //Exercise-1 create a Dog object called myDog
        Dog myDog = new Dog();
        //Exercise-2 print the Dog object you created.
        System.out.println(myDog.toString());
        //Exercise-3 create a new dog and pass in the name "Lassie" to its constructor.
        Dog myDog1 = new Dog("Lassie");
        //Exercise-3 Create a second Dog object with a different name, "Rover" for example.
        Dog myDog2 = new Dog("Rover");
        //Exercise-3 Print the two dog objects.
        System.out.println(myDog1.toString());
        System.out.println(myDog2.toString());
    }
}

Dog.java
// Exercise-1 creating class Dog
public class Dog
{
    //Exercise-2 create a variable at the class level that will represent the dog's name (a String). Initialize it to Lassie
    private String name = "Lassie";
  
    /**Exercise-2
     * toString method that returns the dog's name.
     */
    public String toString()
    {
        return this.name;
    }
  
    /**Exercise-3
     * create a constructor in the Dog class that accepts a parameters which is used to set the variables.
     */
    public Dog(String dogName)
    {
        this.name = dogName;
     }
}

Exercise-4
DogDemo.java
//Exercise-1 creating class DogDemo
public class DogDemo
{
    /**
     * Exercise-1 Static method called makeDogs
     */
    public static void makeDogs()
    {
        /*
        //Exercise-1 create a Dog object called myDog
        Dog myDog = new Dog();
        //Exercise-2 print the Dog object you created.
        System.out.println(myDog.toString());
        //Exercise-3 create a new dog and pass in the name "Lassie" to its constructor.
        Dog myDog1 = new Dog("Lassie");
        //Exercise-3 Create a second Dog object with a different name, "Rover" for example.
        Dog myDog2 = new Dog("Rover");
        //Exercise-3 Print the two dog objects.
        System.out.println(myDog1.toString());
        System.out.println(myDog2.toString());
        */
        //Exercise-4 Define a new Dog objects in makeDogs and give them a name, breed and age.
        Dog myDog3 = new Dog("Fido", "German Sheppard", 3);
        //Exercise-4 print the dog object
        System.out.println(myDog3.toString());
    }
}

Dog.java
// Exercise-1 creating class Dog
public class Dog
{
    //Exercise-2 create a variable at the class level that will represent the dog's name (a String). Initialize it to Lassie
    private String name = "Lassie";
    //Exercise-4 Add another field to the Dog class representing the dog's breed (a String)
    private String breed;
    //Exercise-4 add another field representing the dog's age (an int).
    private int age;
  
    /**Exercise-2
     * toString method that returns the dog's name.
     */
    public String toString()
    {
        //return this.name;
        //Exercise4 Modify the toString method to return a string
        return this.name + " is a " + this.age + "-year-old " + this.breed;
    }
  
    /**Exercise-3
     * create a constructor in the Dog class that accepts a parameters which is used to set the variables.
     */
    public Dog(String dogName, String dogBreed, int dogAge)
    {
        this.name = dogName;
        //Exercise-4 Modify the Dog constructor to set these values as well, based on parameters.
        this.breed = dogBreed;
        this.age = dogAge;
    }
}

Exercise-5
DogDemo.java
//Exercise-1 creating class DogDemo
public class DogDemo
{
    /**
     * Exercise-1 Static method called makeDogs
     */
    public static void makeDogs()
    {
        /*
        //Exercise-1 create a Dog object called myDog
        Dog myDog = new Dog();
        //Exercise-2 print the Dog object you created.
        System.out.println(myDog.toString());
        //Exercise-3 create a new dog and pass in the name "Lassie" to its constructor.
        Dog myDog1 = new Dog("Lassie");
        //Exercise-3 Create a second Dog object with a different name, "Rover" for example.
        Dog myDog2 = new Dog("Rover");
        //Exercise-3 Print the two dog objects.
        System.out.println(myDog1.toString());
        System.out.println(myDog2.toString());
        */
        //Exercise-4 Define a new Dog objects in makeDogs and give them a name, breed and age.
        Dog myDog3 = new Dog("Fido", "German Sheppard", 3);
        //Exercise-4 print the dog object
        System.out.println(myDog3.toString());
        //Exercise-5 get and print just the breed of one of your created objects.
        System.out.println(myDog3.getBreed());
    }
}

Dog.java
// Exercise-1 creating class Dog
public class Dog
{
    //Exercise-2 create a variable at the class level that will represent the dog's name (a String). Initialize it to Lassie
    private String name = "Lassie";
    //Exercise-4 Add another field to the Dog class representing the dog's breed (a String)
    private String breed;
    //Exercise-4 add another field representing the dog's age (an int).
    private int age;
  
    /**Exercise-2
     * toString method that returns the dog's name.
     */
    public String toString()
    {
        //return this.name;
        //Exercise4 Modify the toString method to return a string
        return this.name + " is a " + this.age + "-year-old " + this.breed;
    }
  
    /**Exercise-3
     * create a constructor in the Dog class that accepts a parameters which is used to set the variables.
     */
    public Dog(String dogName, String dogBreed, int dogAge)
    {
        this.name = dogName;
        //Exercise-4 Modify the Dog constructor to set these values as well, based on parameters.
        this.breed = dogBreed;
        this.age = dogAge;
    }
  
    /**Exercise-5
     * Create getter methods for all the three variables
     */
    public String getName()
    {
        return this.name;
    }
  
    public String getBreed()
    {
        return this.breed;
    }
  
    public int getAge()
    {
        return this.age;
    }
}

Exercise-6
DogDemo.java
//Exercise-1 creating class DogDemo
public class DogDemo
{
    /**
     * Exercise-1 Static method called makeDogs
     */
    public static void makeDogs()
    {
        /*
        //Exercise-1 create a Dog object called myDog
        Dog myDog = new Dog();
        //Exercise-2 print the Dog object you created.
        System.out.println(myDog.toString());
        //Exercise-3 create a new dog and pass in the name "Lassie" to its constructor.
        Dog myDog1 = new Dog("Lassie");
        //Exercise-3 Create a second Dog object with a different name, "Rover" for example.
        Dog myDog2 = new Dog("Rover");
        //Exercise-3 Print the two dog objects.
        System.out.println(myDog1.toString());
        System.out.println(myDog2.toString());
        */
        //Exercise-4 Define a new Dog objects in makeDogs and give them a name, breed and age.
        Dog myDog3 = new Dog("Fido", "German Sheppard", 3);
        //Exercise-4 print the dog object
        System.out.println(myDog3.toString());
        //Exercise-5 get and print just the breed of one of your created objects.
        System.out.println(myDog3.getBreed());
        //Exercise-6 try to set the age of yourDog to 0
        myDog3.setAge(0);
        //Exercise-6 print the Dog object to make sure the age did not change.
        System.out.println(myDog3.getAge());
        //Exercise-6 set the age of yourDog to 4 and print it again.
        myDog3.setAge(4);
        System.out.println(myDog3.getAge());
    }
}

Dog.java
// Exercise-1 creating class Dog
public class Dog
{
    //Exercise-2 create a variable at the class level that will represent the dog's name (a String). Initialize it to Lassie
    private String name = "Lassie";
    //Exercise-4 Add another field to the Dog class representing the dog's breed (a String)
    private String breed;
    //Exercise-4 add another field representing the dog's age (an int).
    private int age;
  
    /**Exercise-2
     * toString method that returns the dog's name.
     */
    public String toString()
    {
        //return this.name;
        //Exercise4 Modify the toString method to return a string
        return this.name + " is a " + this.age + "-year-old " + this.breed;
    }
  
    /**Exercise-3
     * create a constructor in the Dog class that accepts a parameters which is used to set the variables.
     */
    public Dog(String dogName, String dogBreed, int dogAge)
    {
        this.name = dogName;
        //Exercise-4 Modify the Dog constructor to set these values as well, based on parameters.
        this.breed = dogBreed;
        this.age = dogAge;
    }
  
    /**Exercise-5
     * Create getter methods for all the three variables
     */
    public String getName()
    {
        return this.name;
    }
  
    public String getBreed()
    {
        return this.breed;
    }
  
    public int getAge()
    {
        return this.age;
    }
  
    /**Exercise-6
     * Add a "setter" method for the age field
     */
    public void setAge(int dogAge)
    {
        //Exercise-6 Don't change the age if the parameter is less than 1.
        if(dogAge >= 1)
            this.age = dogAge;
    }
}

Exercise-7
DogDemo.java
//Exercise-1 creating class DogDemo
public class DogDemo
{
    /**
     * Exercise-1 Static method called makeDogs
     */
    public static void makeDogs()
    {
        /*
        //Exercise-1 create a Dog object called myDog
        Dog myDog = new Dog();
        //Exercise-2 print the Dog object you created.
        System.out.println(myDog.toString());
        //Exercise-3 create a new dog and pass in the name "Lassie" to its constructor.
        Dog myDog1 = new Dog("Lassie");
        //Exercise-3 Create a second Dog object with a different name, "Rover" for example.
        Dog myDog2 = new Dog("Rover");
        //Exercise-3 Print the two dog objects.
        System.out.println(myDog1.toString());
        System.out.println(myDog2.toString());
        */
        //Exercise-4 Define a new Dog objects in makeDogs and give them a name, breed and age.
        Dog myDog3 = new Dog("Fido", "German Sheppard", 3);
        //Exercise-4 print the dog object
        System.out.println(myDog3.toString());
        //Exercise-5 get and print just the breed of one of your created objects.
        System.out.println(myDog3.getBreed());
        //Exercise-6 try to set the age of yourDog to 0
        myDog3.setAge(0);
        //Exercise-6 print the Dog object to make sure the age did not change.
        System.out.println(myDog3.getAge());
        //Exercise-6 set the age of yourDog to 4 and print it again.
        myDog3.setAge(4);
        System.out.println(myDog3.getAge());
        //Exercise-7 print each dog's age in dog-years:Rover is 28 in dog-years.
        System.out.println(myDog3.getName() + " is " + myDog3.getDogYears() + " in dog-years." );
    }
}

Dog.java
// Exercise-1 creating class Dog
public class Dog
{
    //Exercise-2 create a variable at the class level that will represent the dog's name (a String). Initialize it to Lassie
    private String name = "Lassie";
    //Exercise-4 Add another field to the Dog class representing the dog's breed (a String)
    private String breed;
    //Exercise-4 add another field representing the dog's age (an int).
    private int age;
  
    /**Exercise-2
     * toString method that returns the dog's name.
     */
    public String toString()
    {
        //return this.name;
        //Exercise4 Modify the toString method to return a string
        return this.name + " is a " + this.age + "-year-old " + this.breed;
    }
  
    /**Exercise-3
     * create a constructor in the Dog class that accepts a parameters which is used to set the variables.
     */
    public Dog(String dogName, String dogBreed, int dogAge)
    {
        this.name = dogName;
        //Exercise-4 Modify the Dog constructor to set these values as well, based on parameters.
        this.breed = dogBreed;
        this.age = dogAge;
    }
  
    /**Exercise-5
     * Create getter methods for all the three variables
     */
    public String getName()
    {
        return this.name;
    }
  
    public String getBreed()
    {
        return this.breed;
    }
  
    public int getAge()
    {
        return this.age;
    }
  
    /**Exercise-6
     * Add a "setter" method for the age field
     */
    public void setAge(int dogAge)
    {
        //Exercise-6 Don't change the age if the parameter is less than 1.
        if(dogAge >= 1)
            this.age = dogAge;
    }
  
    /**Exercise-7
     * Add a method in Dog called getDogYears that returns the dog's age in dog-years.
     */
    public int getDogYears()
    {
        return this.getAge() * 7;
    }
}