Java prototype design pattern

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Dictionary meaning of Prototype: A first or preliminary version of a device or vehicle from which other forms are developed.

Java prototype design pattern comes under the Creational Design Pattern category and it is used in the situations when a new object creation is costly.

Java prototype design pattern states that if a new object creation is costly than clone original object and then modify it, instead of creating a new object.

Let’s, we have a customer object which is loaded from database and after loading we have to modify its data multiple times. In such situations we have to clone that object instead of creating a new object and loading all data from database again.

Example

Customers.java

package com.w3schools;
 
import java.util.ArrayList;
import java.util.List;
 
public class Customers implements Cloneable{
private List<String> customerList;
 
	public Customers(){
		customerList = new ArrayList<String>();
	}
 
	public Customers(List<String> list){
		this.customerList=list;
	}
	public void loadDataFromDB(){
		//Read all customers from DB
		customerList.add("Bharat");
		customerList.add("Sahdev");
		customerList.add("Richi");
		customerList.add("Jai");
		customerList.add("Bharti");
		customerList.add("Saveta");
		customerList.add("Deepika");
	}
 
	public List<String> getCustomerList() {
		return customerList;
	}
 
	@Override
	public Object clone() throws CloneNotSupportedException{
			List<String> temp = new ArrayList<String>();
			for(String string : this.getCustomerList()){
				temp.add(string);
			}
			return new Customers(temp);
	}
}

PrototypePatternTest.java

package com.w3schools;
 
import java.util.List;
 
public class PrototypePatternTest {
	public static void main(String args[]){
		try {
			Customers customers = new Customers();
			customers.loadDataFromDB();
 
			Customers customers1 = (Customers) customers.clone();
			Customers customers2 = (Customers) customers.clone();
			List<String> customersList1 = customers1.getCustomerList();
			customersList1.add("Vivek");
			List<String> customersList2 = customers2.getCustomerList();
			customersList2.remove("Deepika");
 
			System.out.println("customers List elements: "+customers.getCustomerList());
			System.out.println("customers1 List elements: "+customersList1);
			System.out.println("customers2 List elements: "+customersList2);
		} catch (CloneNotSupportedException e) {
			e.printStackTrace();
		}
	}
}

Output

customers List elements: [Bharat, Sahdev, Richi, Jai, Bharti, Saveta, Deepika]
customers1 List elements: [Bharat, Sahdev, Richi, Jai, Bharti, Saveta, Deepika, Vivek]
customers2 List elements: [Bharat, Sahdev, Richi, Jai, Bharti, Saveta]