Computer Science 313 – Advanced Programming Topics

LECTURE 32: IMPLEMENTING THE COMPOSITE PATTERN

 

Writing a

Java-based file manager  Starts at drive, but drill-down into directories  Considers only directories & files (for now)  Named required for all directory entries  Print out the names of directories & files  Print out files sizes as we traverse directories  Allow user to create & delete files Remain true to our basic nature

 

Writing a

Java-based file manager  Starts at drive, but drill-down into directories  Considers only directories & files (for now)  Named required for all directory entries  Print out the names of directories & files  Print out files sizes as we traverse directories  Allow user to create & delete files Remain true to our basic nature

Composite Pattern Classes

 Create abstract superclass

for the pattern

 This class normally used by client code  Common methods & fields defined in superclass  Should also declare any abstract methods needed  Other classes subclass

of abstract superclass

 Decorator-like parallel hierarchies not required  Subinterfaces not required & almost never used  Could create hierarchies as needed  But consider composition vs. inheritence

Composite Code Inside

public abstract class OSEntry { public String name; public abstract String toString(); public void createFile(String fileName) throws UnsupportedOperationException { throw new UnsupportedOperationException(); } } public void createDir(String dirName) throws UnsupportedOperationException { throw new UnsupportedOperationException(); }

Directories Contain…?

 

Currently,

each directory has lots of files    Will need a field to store these references Could use an array or some type of

List

Question is: what type should

List

hold?

List

could

simply store references to

File

  Unable to hold new types of entries we create Class is forever closed to any type of extension  Containers must refer to abstract superclass

Woot! Pimped-Out Recursion!

public class Directory extends OSEntry { public List contents; public String toString() { String retVal = getName(); for (OSEntry entry : contents) { } } return retVal;

Container Code

public class Directory extends OSEntry { public List contents; public void createFile(String fName) { String newFile = new File(getName(), fName); contents.add(newFile); } public void createDir(String dName) { String dir = new Directory(getName(), dName); contents.add(dir); }

File Methods…

  Files should not be able to create

files & dirs

 Methods declared previously , so that is good   Even better, already throw documented exception Useful trick when option may/may not be possible  Should be careful about too many exceptions

Should be able to

get size of a file  Most classes should not provide this method   Instead, we will not declare this in the superclass Clients must have a

File

before calling method

File Code

public class File extends OSEntry { public java.util.File fileInOS; public String toString() { return getName(); } } public long getSize() { return fileInOS.getLength(); }

Client Code

OSEntry entry; System.out.println(entry.toString()); if (entry instanceof File) { System.out.println(“Size is :” + ((File)entry).getSize()); } else { System.out.println(“No size, bozo!”); }

For Next Class

   Lab available on the web  Lab will be due 2 weeks from Friday No class this Friday  Some percentage of class with me in Hartford, CT  Use time wisely – work on lab, study for the test #2 Test #2 in class on Monday  Can include any and all material since last test  Patterns & optimizations fair game to ask about  Open-note, open-book, open-template, but closed slide