Class
Definition
A class is a blueprint or template for creating objects in object-oriented programming. It defines the properties and behaviors that an object of that class will have.
Analogy
Think of a class as a recipe for baking cookies. The recipe provides instructions on what ingredients to use, how to mix them, and how long to bake them. Similarly, a class provides instructions on what data and methods an object will have.
Related terms
Object: An object is an instance of a class. It represents a specific entity with its own set of data and behavior.
Inheritance: Inheritance is the process by which one class inherits the properties and behaviors of another class. It allows for code reuse and promotes modularity.
Encapsulation: Encapsulation is the practice of hiding internal details of an object and providing access only through well-defined interfaces. It helps maintain code integrity and prevents unauthorized access.
"Class" appears in:
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Study guides (4)
Additional resources (1)
Practice Questions (20+)
Which access level makes a variable, class, or method available only to its own class?
What does a class provide in Java?
Which of the following is NOT a characteristic of a class in Java?
What role does a class play in object-oriented programming?
What is the difference between a class and an object in Java?
What happens if a constructor call doesn't match any of the constructors in a class?
Consider the following method. public int sumNumbers(int num1, int num2, int num3) { /* implementation not shown */ } Which of the following lines of code, if located in a method in the same class as sumNumbers, will compile without an error?
If the class Car is a subclass of the class Vehicle, what happens when Java tries to run the line “Vehicle vehicle = new Car();”?
If the class Bird is a superclass of the class Penguin, what happens when Java tries to run the line “Penguin penguin = new Bird();”?
If class C extends class H, class B extends class H, and class G extends class B, what is the relationship between H and G?
Given the following code: ``` class A { public static void show() { System.out.print("A"); } } class B extends A { public static void show() { System.out.print("B"); } } class C extends B { public static void show() { System.out.print("C"); } } ``` What will be the output when the following code is executed? ``` A obj1 = new C(); B obj2 = new C(); C obj3 = new C(); obj1.show(); obj2.show(); obj3.show(); ```
Given the following code: ``` class A { public void display() { System.out.print("A"); } } class B extends A { public void display() { System.out.print("B"); } } class C extends B { public void display() { System.out.print("C"); } } ``` What will be the output when the following code is executed? ``` B obj1 = new C(); C obj2 = new C(); A obj3 = new C(); obj1.display(); obj2.display(); obj3.display(); ```
Given the following code: ``` class A { public void show() { System.out.println("A"); } } class B extends A { public void show() { System.out.println("B"); } } class C extends B { public void show() { System.out.println("C"); } } ``` What will be the output when the following code is executed? ``` A obj = new C(); obj.show(); ```
Consider the following class hierarchy: ``` class Animal { void makeSound() { System.out.println("Some sound"); } } class Dog extends Animal { void makeSound() { System.out.println("Bark"); } } class Cat extends Animal { void makeSound() { System.out.println("Meow"); } } ``` If we create an object like this: `Animal animal = new Dog();`, what will be printed when we call `animal.makeSound()`?
Given the following code: ``` class A { public static void printMessage() { System.out.println("Hi from A"); } } class B extends A { public static void printMessage() { System.out.println("Hi from B"); } } ``` What will be the output when the following code is executed? ``` B obj = new B(); obj.printMessage(); ```
Given the following code: ``` class A { public void show() { System.out.println("A"); } } class B extends A { public void show() { System.out.println("B"); } } ``` What will be the output when the following code is executed? ``` A obj1 = new A(); B obj2 = new B(); A obj3 = new B(); obj1.show(); obj2.show(); obj3.show(); ```
Given the block of code below, answer the following question: ```java class Person { // constructor not shown public void printGreeting() { System.out.println("Hello! How are you?"); } } class Student extends Person { // constructor not shown } ``` Question: Consider the code above. If we create an object of the `Student` class and call the `printGreeting()` method on that object, what will be outputted?
"Given the block of code below, answer the following question: ```java class Shape { // constructor not shown public void draw() { System.out.println("Drawing a shape"); } } class Circle extends Shape { // constructor not shown public void draw() { System.out.println("Drawing a circle"); super.draw(); } } ``` Question: Consider the code above. If we create an object of the Circle class and call the `draw()` method on that object, what will be the output?
Consider the code below. If we create an object of the Child class and call the `prinMessaget()` method on that object, what will be the output? ```java class Parent { void printMessage() { System.out.println("Hello from Parent"); } } class Child extends Parent { void printMessage() { super.printMessage(); System.out.println("Hello from Child"); } } ```
What output do we get if we run the following code? class X { public X() { System.out.println("X's no-argument constructor is invoked"); } } class Y extends X { public Y() { } } public class Z { public static void main(String[] args) { Y y = new Y(); } }
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