What are Copy Constructors In Java? Explore Types, Examples & Use

A copy constructor is a constructor that creates a new object by copying the values of fields from an existing object of the same class. Unlike languages such as C++, Java does not provide a built-in copy constructor — you write one yourself.

Example

class Student {
    String name;
    int age;

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

    // Copy constructor
    Student(Student other) {
        this.name = other.name;
        this.age = other.age;
    }
}

Student s1 = new Student("Riya", 21);
Student s2 = new Student(s1); // copy of s1

Types of Copying

• Shallow Copy — copies primitive fields and reference values directly, so reference type fields still point to the same objects
• Deep Copy — creates new copies of any referenced objects as well, so the two objects are fully independent

Deep Copy Example

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

class Student {
    String name;
    Address address;

    Student(Student other) {
        this.name = other.name;
        this.address = new Address(other.address); // deep copy
    }
}

When to Use a Copy Constructor

• When you need an independent copy of an object without affecting the original
• When cloning objects that contain mutable fields, to avoid shared-state bugs
• As a cleaner alternative to Java's Cloneable interface and clone() method