Composite Design Pattern

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Problem:

The objective of this exercise is to implement the Composite design pattern.

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Steps:

$1.$ Create an interface called AbstractFile. This is the highest level interface of all component. Define an empty method void ls$()$ in it$.$ It is going to be used to print out the entire content in a directory.

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$2.$ Create a class called File to implements AbstractFile. This the leaf node $($or menu item in slides$).$ The File class should have its constructor, a String instance variable called name.

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$3.$ You need to implement the ls$()$ method by printing out the file name.

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System.out.println$($File: $+$ name$)$;

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$4.$ Create a class called Directory to implements AbstractFile. This is the composite class. It should have its constructor and a String instance variable called name.

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$5.$ Different from File class, we need to add an ArrayList called includedFiles to save all the files and sub$-$directories in it$.$ Also, we need a void add$($AbstractFile file$)$ method to add files and directories to it$.$ Implement this add method by adding the file to the ArrayList includedFiles.

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$6.$ The ls$()$ method in Directory class is different from the one in File. In addition to printing out the directory name, you need to add a for loop to traverse every item in the ArrayList includedFiles, and call its ls$()$ method.

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$7.$ Write a client class and a main function to demonstrate how they work. Add some files and sub$-$directories to the root directory, and add some files to the sub$-$directories. Then, print all of them by calling the ls$()$ method in the root directory.

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What to turn in: Similar as E$5.$