[JAVA] Composite pattern

What is the Composite pattern?

Identify the container and contents to create a recursive structure.

The role of Leaf

A role that represents the "contents". Nothing else can be included in this role.

package composite;

public class File extends Entry{
	private String name;
	private int size;

	public File(String name, int size) {
		this.name = name;
		this.size = size;

	public String getName() {
		return name;

	public int getSize() {
		return size;

	protected void printList(String prefix) {
		System.out.println(prefix + "/" + this);

The role of Composite

A role that represents a "container". You can enter the role of Leaf or Composite.

package composite;

import java.util.ArrayList;
import java.util.Iterator;

public class Directory extends Entry{
	private String name;
	private ArrayList<Entry> directory = new ArrayList<>();

	public Directory(String name) {
		this.name = name;

	public String getName() {
		return name;

	public int getSize() {
		int size = 0;
		Iterator<Entry> it = directory.iterator();
		while (it.hasNext()) {
			Entry entry = (Entry) it.next();
			size += entry.getSize();
		return size;

	public Entry add(Entry entry) {
		return this;

	protected void printList(String prefix) {
		System.out.println(prefix + "/" + this);
		Iterator<Entry> it = directory.iterator();
		while (it.hasNext()) {
			Entry entry = (Entry) it.next();
			entry.printList(prefix + "/" + name);

The role of Component

A role to equate the Leaf role with the Composite role. The Component role is realized as a superclass common to the Leaf role and Composite role.

package composite;

public abstract class Entry {
	public abstract String getName();
	public abstract int getSize();
	protected abstract void printList(String prefix);

	public Entry add(Entry entry) throws FileTreatmentException {
		throw new FileTreatmentException();

	public void printList() {

	public String toString() {
		return getName() + "(" + getSize() + ")";

The role of Client

Users of the Composite pattern.

package composite;

public class Main {
	public static void main(String[] args) {
		try {
			System.out.println("Making root entryies...");
			Directory rootDir = new Directory("root");
			Directory binDir = new Directory("bin");
			Directory tmpDir = new Directory("tmp");
			Directory usrDir = new Directory("usr");
			binDir.add(new File("vi", 10000));
			binDir.add(new File("latex", 20000));
			System.out.println("Making user entryies...");
			Directory yuki = new Directory("yuki");
			Directory hanako = new Directory("hanako");
			Directory tomura = new Directory("tomura");
			yuki.add(new File("diary.html", 100));
			yuki.add(new File("Composite.java", 200));
			hanako.add(new File("memo.tex", 300));
			tomura.add(new File("game.doc", 400));
			tomura.add(new File("junk.mail", 500));
		} catch (FileTreatmentException e) {

Execution result

スクリーンショット 2020-09-09 11.58.42.png


I used this as a reference. Augmented and Revised Introduction to Design Patterns Learned in Java Language

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