Copy Constructor in Java
Prerequisite – Constructors in Java
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.
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Java
// filename: Main.javaclass Complex { private double re, im; // A normal parameterized 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:
Java
// filename: Main.javaclass 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 }} |
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