Copy constructors

A copy constructor creates a new object by copying the state of another object of the same class. Java does not provide a default copy constructor; you must write it yourself.

Example:

class Point {
    int x, y;

    // Regular constructor
    Point(int x, int y) {
        this.x = x;
        this.y = y;
    }

    // Copy constructor
    Point(Point other) {
        this.x = other.x;
        this.y = other.y;
    }
}

Usage:

Point p1 = new Point(10, 20);
Point p2 = new Point(p1);  // p2 is a copy of p1

Deep copy vs shallow copy: For objects containing references, you may need a deep copy.

class Address {
    String city;
    Address(Address other) {
        this.city = other.city;
    }
}

class Person {
    String name;
    Address address;

    // Deep copy constructor
    Person(Person other) {
        this.name = other.name;
        this.address = new Address(other.address); // copy nested object
    }
}

Alternatives: Use clone() method or factory methods, but copy constructors are often clearer.