Composite in Java
Why read if you can watch?
Watch Composite's video tutorialBefore and after
BEFORE
class File
{
public File(String name)
{
m_name = name;
}
public void ls()
{
System.out.println(Composite.g_indent + m_name);
}
private String m_name;
}
class Directory
{
public Directory(String name)
{
m_name = name;
}
public void add(Object obj)
{
m_files.add(obj);
}
public void ls()
{
System.out.println(Composite.g_indent + m_name);
Composite.g_indent.append(" ");
for (int i = 0; i < m_files.size(); ++i)
{
Object obj = m_files.get(i);
// ***** Recover the type of this object ******
if (obj.getClass().getName().equals("Directory"))
((Directory)obj).ls();
else
((File)obj).ls();
}
Composite.g_indent.setLength(CompositeDemo.g_indent.length() - 3);
}
private String m_name;
private ArrayList m_files = new ArrayList();
}
public class CompositeDemo
{
public static StringBuffer g_indent = new StringBuffer();
public static void main(String[] args)
{
Directory one = new Directory("dir111"), two = new Directory("dir222"),
thr = new Directory("dir333");
File a = new File("a"), b = new File("b"), c = new File("c"), d = new
File("d"), e = new File("e");
one.add(a);
one.add(two);
one.add(b);
two.add(c);
two.add(d);
two.add(thr);
thr.add(e);
one.ls();
}
}
dir111
a
dir222
c
d
dir333
e
b
AFTER
// ***** Define a "lowest common denominator" *****
interface AbstractFile
{
public void ls();
}
// ***** File implements the "lowest common denominator"
class File implements AbstractFile
{
public File(String name)
{
m_name = name;
}
public void ls()
{
System.out.println(CompositeDemo.g_indent + m_name);
}
private String m_name;
}
// ***** Directory implements the "lowest common denominator"
class Directory implements AbstractFile
{
public Directory(String name)
{
m_name = name;
}
public void add(Object obj)
{
m_files.add(obj);
}
public void ls()
{
System.out.println(CompositeDemo.g_indent + m_name);
CompositeDemo.g_indent.append(" ");
for (int i = 0; i < m_files.size(); ++i)
{
// ***** Leverage the "lowest common denominator"
AbstractFile obj = (AbstractFile)m_files.get(i);
obj.ls();
}
CompositeDemo.g_indent.setLength(CompositeDemo.g_indent.length() - 3);
}
private String m_name;
private ArrayList m_files = new ArrayList();
}
public class CompositeDemo
{
public static StringBuffer g_indent = new StringBuffer();
public static void main(String[] args)
{
Directory one = new Directory("dir111"), two = new Directory("dir222"),
thr = new Directory("dir333");
File a = new File("a"), b = new File("b"), c = new File("c"), d = new
File("d"), e = new File("e");
one.add(a);
one.add(two);
one.add(b);
two.add(c);
two.add(d);
two.add(thr);
thr.add(e);
one.ls();
}
}
