Apex Constructors
A constructor in Apex is a special method that runs automatically when an object of a class is created. It’s used to initialize the values of class variables when the object is made.
A constructor:
• Has the same name as the class.
• Does not return any value, not even void.
• Can be default (no parameters) or parameterized (with input values).
1. Default Constructor
A default constructor doesn’t take any parameters.
Example:
public class Student {
public String name;
public Integer age;
// Default constructor
public Student() {
name = ‘Not Set’;
age = 0;
}
public void showDetails() {
System.debug(‘Name: ‘ + name);
System.debug(‘Age: ‘ + age);
}
}
Student s1 = new Student();
s1.showDetails();
Code Explanation:
• The Student() constructor runs when new Student() is called.
• It sets default values for name and age.
• s1.showDetails() prints those default values.
Output:
Name: Not Set
Age: 0
2. Parameterized Constructor
This constructor takes values and sets them while creating the object.
Example:
public class Book {
public String title;
public String author;
// Parameterized constructor
public Book(String t, String a) {
title = t;
author = a;
}
public void showInfo() {
System.debug(‘Title: ‘ + title);
System.debug(‘Author: ‘ + author);
}
}
Book b1 = new Book(‘Atomic Habits’, ‘James Clear’);
b1.showInfo();
Code Explanation:
• Book(String t, String a) is a constructor with parameters.
• new Book(‘Atomic Habits’, ‘James Clear’) sets the title and author.
• b1.showInfo() prints the values.
Output:
Title: Atomic Habits
Author: James Clear
3. Multiple Constructors (Overloading)
Apex supports constructor overloading, meaning you can define multiple constructors in one class with different parameters.
Example:
public class Employee {
public String name;
public Integer salary;
// Default constructor
public Employee() {
name = ‘Unknown’;
salary = 0;
}
// Parameterized constructor
public Employee(String n, Integer s) {
name = n;
salary = s;
}
public void printInfo() {
System.debug(‘Name: ‘ + name);
System.debug(‘Salary: ‘ + salary);
}
}
Employee e1 = new Employee();
e1.printInfo();
Employee e2 = new Employee(‘Alice’, 50000);
e2.printInfo();
Code Explanation:
• Two constructors: one with no arguments, one with two arguments.
• Depending on how the object is created, the correct constructor is called.
Output:
Name: Unknown
Salary: 0
Name: Faiz
Salary: 50000
Constructors Save Time
Constructors help us quickly set up an object with default or given values at the moment it’s created — instead of setting each value manually one by one.
Real-life Analogy
Imagine you’re ordering a custom pizza online.
• Without a constructor: you call and say, “Add cheese. Now add olives. Now add mushrooms…”
• With a constructor: you choose “Cheese + Olive + Mushroom” from a preset combo with one click.
Constructors = Instant Setup
Without constructors = Manual Setup Step-by-Step
Tasks for Practice
Task 1: Create a class Car with properties: brand and model. Use a constructor to set the values and print them using a method.
Task 2: Create a class Person with a default constructor that sets name to "No Name" and age to 0. Print the data.
Task 3: Create a class Movie with multiple constructors. One should set only the title, and the other should set both title and rating. Print the values.
Task 4: Create a class Rectangle with length and width. Use a constructor to set the values and create a method area() to return area.
Task 5: Create a class called Car with two properties:
• String brand
• Integer modelYear Create a default constructor that assigns default values, and print them by creating an object.
Task 6: Create a class called Employee with:
• String name
• Decimal salary Write a parameterized constructor to initialize these fields. Then, create an object by passing values and print the data.
Task 7: Create a class Rectangle with properties length and width.
• Write two constructors:
One that takes no parameters and assigns default values
One that takes two parameters to assign custom values
Create both types of objects and print the area.
Task 8: Create a class Person with name and age.
Inside the constructor, call a method displayInfo() that prints the name and age.
Then, create an object to trigger the output.
