Like C++, Java also supports copy constructor. But, unlike C++, Java doesn’t create a default copy constructor if you don’t write your own.

Following is an example Java program that shows a simple use of copy constructor.

// filename: Main.java

class Complex {

private double re, im;

// A normal parametrized constructor
public Complex(double re, double im) {
this.re = re;
this.im = im;
}

// copy constructor
Complex(Complex c) {
System.out.println("Copy constructor called");
re = c.re;
im = c.im;
}

// Overriding the toString of Object class
@Override
public String toString() {
return "(" + re + " + " + im + "i)";
}
}

public class Main {

public static void main(String[] args) {
Complex c1 = new Complex(10, 15);

// Following involves a copy constructor call
Complex c2 = new Complex(c1);

// Note that following doesn't involve a copy constructor call as
// non-primitive variables are just references.
Complex c3 = c2;

System.out.println(c2); // toString() of c2 is called here
}
}
Output:

Copy constructor called
(10.0 + 15.0i)

Now try the following Java program:

// filename: Main.java

class Complex {

private double re, im;

public Complex(double re, double im) {
this.re = re;
this.im = im;
}
}

public class Main {

public static void main(String[] args) {
Complex c1 = new Complex(10, 15);
Complex c2 = new Complex(c1); // compiler error here
}
}