Design pattern ~ Prototype ~

1.First of all

We will summarize the ** Prototype pattern ** in the GoF design pattern.

2. What is the Prototype pattern?

--The English word Prototype means ** prototype ** or ** model **. --The Prototype pattern is a method that ** creates another instance from an instance ** instead of creating an instance from the class with new xxx (). --The operation to make a duplicate is called ** clone **. --In the GoF design pattern, it is classified as ** Design pattern for generation **.

3. Sample class diagram

4. Sample program

A program that underlines or encloses the entered character string.

4-1. Product interface

An interface that defines replication methods. It inherits the Cloneable interface of java.

Product.java

package framework;
import java.lang.Cloneable;

public interface Product extends Cloneable {
    public abstract void use(String s);
    public abstract Product createClone();
}

4-2. Manager class

This class gives instructions and manages product creation.

Manager.java

package framework;
import java.util.HashMap;

public class Manager {

	private HashMap showcase = new HashMap();

	public void register(String name, Product proto) {
        showcase.put(name, proto);
    }

	public Product create(String protoname) {
        Product p = (Product)showcase.get(protoname);
        return p.createClone();
    }
}

4-3. UnderlinePen class

A class that implements the Product interface. This class is a "underline letters" class.

UnderlinePen.java

import framework.Product;

public class UnderlinePen implements Product {

	private char ulchar;

	public UnderlinePen(char ulchar) {
        this.ulchar = ulchar;
    }

	public void use(String s) {

		int length = s.getBytes().length;

		System.out.println(s);

        for (int i = 0; i < length; i++) {
            System.out.print(ulchar);
        }

        System.out.println("");
    }

	public Product createClone() {
        Product p = null;
        try {
            p = (Product)clone();
        } catch (CloneNotSupportedException e) {
        	//Exception thrown when the object's class does not implement the Cloneable interface
            e.printStackTrace();
        }
        return p;
    }
}

4-4. MessageBox class

A class that implements the Product interface. This class is a "enclose character" class.

MessageBox.java

import framework.Product;

public class MessageBox implements Product {

	private char decochar;

	public MessageBox(char decochar) {
        this.decochar = decochar;
    }

	public void use(String s) {

		int length = s.getBytes().length;

		for (int i = 0; i < length + 2; i++) {
            System.out.print(decochar);
        }

		System.out.println("");
        System.out.println(decochar + s + decochar);

        for (int i = 0; i < length + 2; i++) {
            System.out.print(decochar);
        }

        System.out.println("");
    }

	public Product createClone() {
		Product p = null;
		try {
            p = (Product)clone();
        } catch (CloneNotSupportedException e) {
        	//Exception thrown when the object's class does not implement the Cloneable interface
        	e.printStackTrace();
        }
        return p;
    }
}

4-5. Main class

This class performs the main processing.

Main.java

import framework.Manager;
import framework.Product;

public class Main {
    public static void main(String[] args) {

        Manager manager = new Manager();
        UnderlinePen upen = new UnderlinePen('~');
        MessageBox mbox = new MessageBox('*');
        MessageBox pbox = new MessageBox('+');
        manager.register("strong message", upen);
        manager.register("warning box", mbox);
        manager.register("slash box", pbox);

        Product p1 = manager.create("strong message");
        p1.use("Hello world");
        Product p2 = manager.create("warning box");
        p2.use("Hello world");
        Product p3 = manager.create("slash box");
        p3.use("Hello world");
    }
}

4-6. Execution result

Hello World
===========
*************
*Hello World*
*************
+++++++++++++
+Hello World+
+++++++++++++

5. Benefits

Although it was a relatively simple case in the sample program, creating an instance may require complicated processing or time-consuming processing. It would be very inefficient to do new xxx () every time you create an instance. You can easily create an instance just by creating a Prototype and copying it.

6. GitHub

• https://github.com/i-tanaka730/design_pattern

7. List of design patterns

-** GoF design pattern summary **

8. Reference

This article and sample program were created based on the following books.

-** Introduction to design patterns learned in Java language **

It was very easy to understand and I learned a lot. Thank you. The detailed explanations of the design patterns and sample programs are written, so please take a look at the books as well.