Composite Design Pattern

Composite Design Pattern comes under Structural Design Pattern.

The Composite Design Pattern is used when a class has a group of its own class, and they all share a common interface. it makes it easy to manage, add and remove further end or leaf nodes.

new functionality can be added to the common interface which root, intermediate, and leaf nodes can implement without breaking existing functionality hence following the Open/Closed Principle.

Sometimes a group of objects is connected to each other in a hierarchical manner, and each parent can have multiple children who have almost similar properties as the parent. It's like a tree structure, in which there would be a root or parent node, an end or leaf node, and intermediate nodes connecting root nodes to leaf nodes.

Some real-world examples of Composite Design Patterns are

An owner of the company is a type of employee, then under him/her, there are multiple employees or leaf nodes such as CEO, CFO, and CTO, each leaf node has its own further composite nodes, such as managers, leads and employee or end leaf nodes.

A packaging box or root has a lot of small or intermediate packaging box inside which contains the actual fragile items or leaf nodes. Armys or root nodes have a hierarchical structure. each army consists of divisions or intermediate nodes, divisions is a set of brigades or intermediate nodes, brigades is a set of platoons or intermediate nodes, platoons are a set of squads or intermediate nodes, and squads are groups of soldiers or leaf nodes.

package org.wesome.design.patterns;

public interface Fruit {
    void process();
}

package org.wesome.design.patterns;

import java.util.ArrayList;
import java.util.List;

public class Apple implements Fruit {
    private final List<Fruit> recipeList = new ArrayList<>();

    @Override
    public void process() {
        recipeList.forEach(System.out::println);
    }

    public void addRecipe(Fruit recipe) {
        recipeList.add(recipe);
    }
}

package org.wesome.design.patterns;

import lombok.AllArgsConstructor;
import lombok.NoArgsConstructor;

@AllArgsConstructor
@NoArgsConstructor
public class CrushedApple implements Fruit {
    String state;

    @Override
    public void process() {
        System.out.println("Apple can be " + state);
    }
}

package org.wesome.design.patterns;

import lombok.AllArgsConstructor;
import lombok.NoArgsConstructor;

@AllArgsConstructor
@NoArgsConstructor
public
class Juice implements Fruit {
    String state;

    @Override
    public void process() {
        System.out.println("Juice can be made from " + state + " Apple.");
    }
}

package org.wesome.design.patterns;

import lombok.AllArgsConstructor;
import lombok.NoArgsConstructor;

@AllArgsConstructor
@NoArgsConstructor
public
class Vine implements Fruit {
    String state;

    @Override
    public void process() {
        System.out.println("Vine can be made from " + state + " Apple.");
    }
}

package org.wesome.design.patterns;

import lombok.AllArgsConstructor;
import lombok.NoArgsConstructor;

@AllArgsConstructor
@NoArgsConstructor
public
class CutApple implements Fruit {
    String state;

    @Override
    public void process() {
        System.out.println("Apple can be " + state + " in small pieces.");
    }
}

package org.wesome.design.patterns;

import lombok.AllArgsConstructor;
import lombok.NoArgsConstructor;

@AllArgsConstructor
@NoArgsConstructor
public
class Salad implements Fruit {
    String state;

    @Override
    public void process() {
        System.out.println("Salad can be made from apple " + state + " in small pieces.");
    }
}

package org.wesome.design.patterns;

public class Composite {
    public static void main(String[] args) {
        Fruit crushed = new CrushedApple("crush");
        Fruit juice = new Juice("crush");
        Fruit vine = new Vine("crush");

        Fruit cutInPieces = new CutApple("cut");
        Fruit salad = new Salad("cut");

        Apple apple = new Apple();
        apple.addRecipe(crushed);
        apple.addRecipe(juice);
        apple.addRecipe(vine);

        apple.addRecipe(cutInPieces);
        apple.addRecipe(salad);
        apple.process();
    }
}

plugins {
    id 'java'
    id "io.freefair.lombok" version "6.2.0"
}

group = 'org.wesome'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = JavaVersion.VERSION_1_8

configurations {
    compileOnly {
        extendsFrom annotationProcessor
    }
}
repositories {
    mavenCentral()
}

dependencies {
    implementation 'org.junit.jupiter:junit-jupiter:5.6.2'
}

test {
    useJUnitPlatform()
}