Constructor
Definition
A constructor is a special method within a class that is used to initialize objects of that class. It is called automatically when an object is created and helps set initial values for its attributes.
Analogy
Imagine you're at a bakery ordering a customized cake. The constructor is like the baker who takes your order and prepares the cake according to your specifications before handing it over to you. It ensures that every new object starts off with the necessary setup.
Related terms
Class: A class is a blueprint or template for creating objects in object-oriented programming. Constructors belong to classes and define how objects of that class should be initialized.
Instance variables: Instance variables are attributes or properties associated with each instance (object) of a class. Constructors often assign initial values to these instance variables.
Overloading: Constructor overloading allows multiple constructors within the same class, but with different parameter lists. This provides flexibility in creating objects with varying initialization options.
"Constructor" appears in:
Study guides (6)
Additional resources (3)
Practice Questions (20+)
What is the purpose of a constructor in a class?
What is the purpose of a constructor?
What happens when a constructor changes the data of an object?
What is the signature of a constructor?
Which constructor will be called when creating the following object: Student john = new Student("John", 20);
What happens if a constructor has fewer parameters than the full constructor?
Suppose there is a Car object whose constructor takes the brand (String) and year (int) parameters. If we create two new objects "Car c1 = new Car("Toyota", 2005);" and "Car c2 = new Car("Toyota", 2005);" what will be the output of "System.out.println(c1.equals(c2));"?
Suppose there is a Car class that extends the Vehicle class and whose constructor takes in the “brand” and “year” parameters. What is the static type and dynamic type of the variable "lambo" in the following code? ``` Car lambo = new Car(“Lamborghini”, 2005); ```
"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?
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(); } }
If a superclass's constructor takes in four parameters, how many parameters should the subclass's constructor have?
If a subclass's constructor doesn't explicitly call its superclass's constructor using super, Java will:
Given the block of code below, answer the following question: ```java class Animal { // constructor not shown } class Dog extends Animal { // constructor not shown public void makeSound() { System.out.println("Woof! Woof!"); } } ``` Question: Consider the code above. If we create an object of the `Dog` class and call the `makeSound()` method on that object, what will be outputted?
When writing constructors for subclasses, which keyword is used to invoke the superclass's constructor?
What kind of access is associated with the constructor of a class?
What is the purpose of a constructor in Java?
What happens if a class does not have a constructor?
How is the Assignment class constructor defined?
Can a constructor have a return type in Java?
Why does the following code not compile? public class Student { private int gpa; public getGPA() { return gpa; } // Constructor not shown }
Resources
© 2024 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.