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Copy Constructor in Java

  • Difficulty Level : Easy
  • Last Updated : 17 May, 2021

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. 

Java




// filename: Main.java
 
class 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.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
    }
}


Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
 


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