Constructor - this

this() is used to call another constructor within the same class.
Helps avoid code duplication when multiple constructors share logic.

Example

class Car {
    String moel;
    int year;
    
    Car() {
        this("Unknown", 2020); // calls second constructor
    }
    
    Car(String model, int year) {
        this.model = model;
        this.year = year;
    }
}

Key Rules

• Must be the first statement in the constructor.
• Can only be used once per constructor.
• Cannot be used with super() in the same constructor.

Comparison

this() vs super()

Keyword	Calls…	Used For
this()	Another constructor (same class)	Constructor chaining within class
super()	Parent class constructor	Inheritance-base constructor chaining

Tip

Use this() for constructor chaining when you have default values or shared logic.
Never use this() and super()together - Java won’t allow it.

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Parent: _OOP