Java Copy Constructor

Sometimes we need to clone an object in Java, but not a reference (a junior developer may use). There are several ways to achieve this task; however, I recommend to use a copy-constructor (that comes from C++) and, in particular, using @Builder from Lombok (to avoid boilerplate code))

 

	package cl.devweb.constructor;
	public class Cliente implements Cloneable {
	int rut;
	String nombre;
	Cliente(int rut, String nombre) {
	this.rut = rut;
	this.nombre = nombre;
	}
	// copy constructor
	Cliente(Cliente c) {
	System.out.println("Copy constructor");
	rut = c.rut;
	nombre = c.nombre;
	}
	public Object clone() throws CloneNotSupportedException {
	return super.clone();
	}
	public int getRut() {
	return rut;
	}
	public void setRut(int rut) {
	this.rut = rut;
	}
	public String getNombre() {
	return nombre;
	}
	public void setNombre(String nombre) {
	this.nombre = nombre;
	}
	}

view raw Cliente.java hosted with ❤ by GitHub

	package cl.devweb.constructor;
	public class ClienteClonePoc {
	public static void main(String[] args) {
	try {
	Cliente cliente1 = new Cliente(1, "joe");
	Cliente cliente2 = (Cliente) cliente1.clone();
	Cliente cliente3 = new Cliente(cliente1);
	Cliente cliente4 = cliente1;
	cliente1.setRut(7);
	cliente1.setNombre("john");
	System.out.println("cliente1: " + cliente1.getRut() + " " + cliente1.getNombre());
	System.out.println("cliente2: " + cliente2.getRut() + " " + cliente2.getNombre());
	System.out.println("cliente3: " + cliente3.getRut() + " " + cliente3.getNombre());
	System.out.println("cliente4: " + cliente4.getRut() + " " + cliente4.getNombre());
	} catch (CloneNotSupportedException c) {
	c.printStackTrace();
	}
	}
	}

view raw ClienteClonePoc.java hosted with ❤ by GitHub

	package cl.devweb.constructor;
	public class CopyConstructorPocLombok {
	public static void main(String[] args) {
	Premium premium1 = new Premium("pi", 3.14);
	Premium premium2 = premium1.toBuilder().build(); //copy constructor
	Premium premium3 = premium1;
	premium1.setNameOption("e");
	premium1.setPremiumValue(2.718);
	System.out.println("premium1: " + premium1.getNameOption() + " " + premium1.getPremiumValue());
	System.out.println("premium2: " + premium2.getNameOption() + " " + premium2.getPremiumValue());
	System.out.println("premium3: " + premium3.getNameOption() + " " + premium3.getPremiumValue());
	}
	}

view raw CopyConstructorPocLombok.java hosted with ❤ by GitHub

	package cl.devweb.constructor;
	import com.fasterxml.jackson.annotation.JsonAlias;
	import lombok.AllArgsConstructor;
	import lombok.Builder;
	import lombok.Getter;
	import lombok.NoArgsConstructor;
	import lombok.Setter;
	@Builder(toBuilder=true)
	@NoArgsConstructor
	@AllArgsConstructor
	@Getter
	@Setter
	public class Premium {
	@JsonAlias("nombreOpcion")
	private String nameOption;
	@JsonAlias("valor")
	private double premiumValue;
	}

view raw Premium.java hosted with ❤ by GitHub