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What are copy constructors in Java?
Generally, the copy constructor is a constructor which creates an object by initializing it with an object of the same class, which has been created previously.
Java supports for copy constructors but unlike C language, Java does not provide an explicit copy constructor you need to define it yourself.
writing a copy constructor
Usually, to initialize the values of instance variables of a class (one way) we create a parameterized constructor accepting the values for all instance variables and initialize them with the given values.
int name;
int age;
public Student(String name, int age){
this.name = name;
this.age = age;
}But, in a copy constructor accept an object of the current class and initialize the values of instance variables with the values in the obtained object.
public Student(Student std){
this.name = std.name;
this.age = std.age;
}Then from the if you create an object and invoke the copy constructor by passing it, you will get a copy of the object you have created earlier.
Student std = new Student("nameValue", ageValue);
Student copyOfStd = new Student(std);Example
Following is an example demonstrating the copy constructors in Java.
import java.util.Scanner;
public class Student {
private String name;
private int age;
public Student(String name, int age){
this.name = name;
this.age = age;
}
public Student(Student std){
this.name = std.name;
this.age = std.age;
}
public void displayData(){
System.out.println("Name : "+this.name);
System.out.println("Age : "+this.age);
}
public static void main(String[] args) {
Scanner sc =new Scanner(System.in);
System.out.println("Enter your name ");
String name = sc.next();
System.out.println("Enter your age ");
int age = sc.nextInt();
Student std = new Student(name, age);
System.out.println("Contents of the original object");
std.displayData();
System.out.println("Contents of the copied object");
Student copyOfStd = new Student(std);
copyOfStd.displayData();
}
}Output
Enter your name Krishna Enter your age 20 Contents of the original object Name : Krishna Age : 20 Contents of the copied object Name : Krishna Age : 20
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