Creating a Java Cat Class with Default Constructor

Last update on May 15 2025 13:07:32 (UTC/GMT +8 hours)

Default Constructor

Write a Java program to create a class called “Cat” with instance variables name and age. Implement a default constructor that initializes the name to "Unknown" and the age to 0. Print the values of the variables.

Sample Solution:

Java Code:

Cat.java

// Define the Cat class
public class Cat {
    // Private instance variables
    private String name;
    private int age;
    // Default constructor
    public Cat() {
        // Initialize name to "Unknown"
        this.name = "Unknown";
        // Initialize age to 0
        this.age = 0;
    }
    // Getter for name
    public String getName() {
        return name;
    }
    // Getter for age
    public int getAge() {
        return age;
    }
    // Main method to test the Cat class
    public static void main(String[] args) {
        // Create a new Cat object using the default constructor
        Cat myCat = new Cat();
        // Use the getter methods to access private variables
        System.out.println("Cat's Name: " + myCat.getName());
        System.out.println("Cat's Age: " + myCat.getAge());
    }
}

Output:

Cat's Name: Unknown
Cat's Age: 0

Explanation:

Define the Cat class:

The Cat class is defined with the keyword class.

Private instance variables:

The Cat class has two private instance variables: name (a String) and age (an int).

Default constructor:

The default constructor Cat() is defined.
Inside the default constructor, name is initialized to "Unknown".
age is initialized to 0.

Main method:

The main method is defined to test the Cat class.
A new Cat object (myCat) is created using the default constructor.
The values of the instance variables (name and age) are printed to the consol

Note on Constructors:

In the above exercise, the default constructor for the Cat class works by:

Initialization: When a new Cat object is created, the default constructor is called automatically.
Setting Default Values: The constructor initializes the name to "Unknown" and the age to 0, ensuring that these variables have default values when an object is created without specific values provided.
Encapsulation: By keeping the instance variables private and initializing them through the constructor, the class ensures that the variables are always set to a known state when an object is created.

For more Practice: Solve these Related Problems:

Write a Java program where the "Cat" class includes a method to set a cat's breed.
Write a Java program where the "Cat" class supports a method to determine if a cat is a kitten (age < 1 year).
Write a Java program where the "Cat" class allows setting and getting the cat’s weight.
Write a Java program where the "Cat" class includes a method to compare the ages of two cats.

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