Constructor Chaining in Java

Constructor chaining is the process of calling one constructor from another constructor within the same class, or from a constructor in the superclass. It's done using the this() and super() keywords.

Chaining Within the Same Class — this()

class Student {
    String name;
    int age;

    Student() {
        this("Unknown", 0);
        System.out.println("Default constructor called");
    }

    Student(String name, int age) {
        this.name = name;
        this.age = age;
    }
}

Chaining to the Superclass — super()

class Person {
    Person(String name) {
        System.out.println("Person constructor: " + name);
    }
}

class Employee extends Person {
    Employee(String name) {
        super(name);
        System.out.println("Employee constructor");
    }
}

Rules of Constructor Chaining

• this() or super() must be the first statement in a constructor
• A constructor cannot call both this() and super() at the same time
• If neither is written explicitly, Java inserts an implicit call to super()

Why Use Constructor Chaining?

• Avoids duplicating initialization code across multiple constructors
• Ensures a common initialization path is always followed
• Makes it easier to maintain default values in one place