[Object-Oriented Design] interview questions #11

Approach

Many candidates may see this problem and instantly panic. A file system seems so low level!
저도 패닉에 빠졌습니다...
The simplest version: Files / Directories
Entry class, File class, Directory class

Solution

public abstract class Entry {
    protected Directory parent;
    protected long created;
    protected long lastUpdated;
    protected long lastAccessed;

    public Entry(String n, Directory p) {
        name = n;
        parent = p;
        created = System.currentTimeMillis();
        lastUpdated = System.currentTimeMillis();
        lastAccessed = System.currentTimeMillis();
    }

    public boolean delete() {
        if(parent == null) return false;
        return parent.deleteEntry(this);
    }

    public abstract int size();

    public String getFullPath() {
        if(parent == null) return name;
        else return parent.getFullPath() + "/" + name;
    }

    //Getter / Setter
    public long getCreateTime() { return created;}
    public long getLastUpdatedTime() { return lastUpdated;}
    public long getLastAccessedTime() { return lastAccessed;}
    public void changeName(String n) { name = n;}
    public String getName() { return name;}
}

public class File extends Entry {
    private String content;
    private int size;
    public File(String n, Directory p, int sz) {
        super(n, p);
        size = sz;
    }

    public int size() {return size;}
    public String getContents(String c) { content = c;}
}

public class Directory extends Entry {
    protected ArrayList<Entry> contents;

    public Directory(String n, Directory p) {
        super(n,p);
        contents = new ArrayList<Entry>();      
    }

    public int size() {
        int size = 0;
        for(Entry e : contents) {
            size += e.size();
        }
        return size;
    }

    public int numberOfFiles() {
        int count = 0;
        for(Entry e : contents) {
            if(e instanceof Directory) {
                count ++; // Directory counts as a file
                Directory d = (Directory) e;
                count += d.numberOfFiles();
            } else if (e instanceof File) {
                count++;
            }
        }
        return count;
    }

    public boolean deleteEntry(Entry entry) {
        return contents.remove(entry);
    }

    public void addEntry(Entry entry) {
        contents.add(entry);
    }

    protected ArrayList<Entry> getContents() { return contents;}
}

interview-preparation / what-we-do

[Object-Oriented Design] interview questions #11 #118

Approach

Solution