"Graphic design patterns," the study notes 5-1 composite mode

Composite pattern that is a combination mode. It can make the container and the contents have consistency, to create a recursive structure .

For example: in the file system, the contents of both folders, but also a container, having a consistency Thus, the file system form a recursive structure. The combination mode is used to create such a structure.

Code

The following code to the file system as an example to achieve a combined mode.

UML

Entry class

It represents a directory entry, the extracted common attributes of files and folders.

public abstract class Entry {
    public abstract String getName();                               
    public abstract int getSize();                                 

    public Entry add(Entry entry) throws RuntimeException {   
        throw new RuntimeException();
    }

    public void printList() {                                      
        printList("");
    }

    protected abstract void printList(String prefix);              

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

File type

It represents a file

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);
    }
}

Directory class

Indicates a folder

public class Directory extends Entry {
    private String name;                    
    private ArrayList directory = new ArrayList();     
    public Directory(String name) {  
        this.name = name;
    }
    public String getName() {
        return name;
    }
    //获取文件夹的总大小，递归操作
    public int getSize() {
        int size = 0;
        Iterator 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;
    }
    protected void printList(String prefix) {
        System.out.println(prefix + "/" + this);
        Iterator it = directory.iterator();
        while (it.hasNext()) {
            Entry entry = (Entry)it.next();
            entry.printList(prefix + "/" + name);
        }
    }
}

Main category

public class Main {
    public static void main(String[] args) {
        try {
            System.out.println("创建根目录");
            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("创建用户目录");
            Directory xiaoming = new Directory("小明");
            Directory xiaohong = new Directory("小红");
            Directory xiaohua = new Directory("小花");
            usrdir.add(xiaoming);
            usrdir.add(xiaohong);
            usrdir.add(xiaohua);
            xiaoming.add(new File("diary.html", 100));
            xiaoming.add(new File("Composite.java", 200));
            xiaohua.add(new File("memo.tex", 300));
            xiaohong.add(new File("game.doc", 400));
            xiaohong.add(new File("junk.mail", 500));
            rootdir.printList();
        } catch (FileTreatmentException e) {
            e.printStackTrace();
        }
    }
}

结果
/*
创建根目录
/root (size : 30000)
/root/bin (size : 30000)
/root/bin/vi (size : 10000)
/root/bin/latex (size : 20000)
/root/tmp (size : 0)
/root/usr (size : 0)

创建用户目录
/root (size : 31500)
/root/bin (size : 30000)
/root/bin/vi (size : 10000)
/root/bin/latex (size : 20000)
/root/tmp (size : 0)
/root/usr (size : 1500)
/root/usr/小明 (size : 300)
/root/usr/小明/diary.html (size : 100)
/root/usr/小明/Composite.java (size : 200)
/root/usr/小红 (size : 900)
/root/usr/小红/game.doc (size : 400)
/root/usr/小红/junk.mail (size : 500)
/root/usr/小花 (size : 300)
/root/usr/小花/memo.tex (size : 300)
*/

Character

The Component : Leaf and Composite is the role of the parent, contain consistent information which has two roles. In this case, the Entry to play this role.

Leaf : represents the role of content, which can not be put into other objects. In this case by the File to play this role.

Composite : represents the role of the container, which can be placed Leaf or Composite roles. In this case by the Directory to play this role.

Client : Use Composite role model, in this case played by the Main.

UML

idea

This mode is very embody the idea of recursion. Composite inherit and a combination of the Component , good taste.