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;
	}

	@Override
	public String getName() {
		return name;
	}

	@Override
	public int getSize() {
		return size;
	}

	@Override
	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;
	}

	@Override
	public String getName() {
		return name;
	}

	@Override
	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) {
		directory.add(entry);
		return this;
	}

	@Override
	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() {
		printList("");
	}

	@Override
	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");
			rootDir.add(binDir);
			rootDir.add(tmpDir);
			rootDir.add(usrDir);
			binDir.add(new File("vi", 10000));
			binDir.add(new File("latex", 20000));
			rootDir.printList();
			
			System.out.println();
			
			System.out.println("Making user entryies...");
			Directory yuki = new Directory("yuki");
			Directory hanako = new Directory("hanako");
			Directory tomura = new Directory("tomura");
			usrDir.add(yuki);
			usrDir.add(hanako);
			usrDir.add(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));
			rootDir.printList();
		} catch (FileTreatmentException e) {
			e.printStackTrace();
		}
	}
}

Execution result

https://github.com/aki0207/composite

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