Constructors

Constructors

Concept of Constructors

• Constructors are special methods in a class that are automatically called when an object of that class is created.
• They typically have the same name as the class and do not have a return type.

Purpose of Constructors

• Constructors are used to initialise the instance variables of a class.
• They can ensure that an object is in a consistent state by default at the time of its creation.

Structure of Constructors

• A class can have multiple constructors, and they can have different parameters.
• They can call other constructors in the same class using the keyword this.
• If no constructor is explicitly defined, Java provides a default constructor with no parameters.

Constructor in Action

• For a class Student with instance variable name, a constructor may be:

public class Student {
    private String name;

    public Student(String name) {
        this.name = name;
    }
}

• The above constructor Student sets the name attribute when a Student object is created.

Role in Application Development

• Constructors play a crucial role in object-oriented programming, ensuring objects are properly initialised.
• They provide flexibility by allowing different ways to create objects, each with different initial states.

Java Specifics

• In Java, if a class doesn’t define any constructor, the compiler automatically creates a default constructor with no arguments.
• The use of this in a constructor refers to the current object being created.

Best Practices

• Use constructors to set mandatory attributes of a class.
• Avoid performing complex operations in constructors; they should be simple and only related to initialising the object.
• Follow the principle of least astonishment; your constructors should not behave in unexpected ways.
• Ensure that constructors do not leave objects in a state where methods can’t be called on them. This is known as making an object “fail-safe”.