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SCJP: Using File object (Part 2) Create a File Finder

Well, continuing with the use of File object, now we are woing to apply some of the key functions to build a simple file finder that is cross plattform, probably more powerful than Windows File Finder XD . The requeriment to satisfy with the file finder are:

"Show all the coincidences of files that name matches with file name entered by user, looking on all the files and sub directories of the directory specified by user."

Let's start!!

Firs of all, create a class named, for example, FileFinder, with main method (it will be an application without GUI), and create a List property, in my case i'm going to call it coincidencesLst, like this:

import java.util.List;
import java.util.ArrayList;

public class FileFinder {
    public FileFinder() {
        coincidencesLst = new ArrayList();
    }
    public static void main(String[] args) {
        //Magic will be here
    }
    private List coincidencesLst;
    public List getCoincidencesLst() {
        return coincidencesLst;
    }
}

The logic of our application will be the next (in that order):

• Ask the user for the file name that he wants to find
• Ask the user for the directory where he wants to find the file
• Search the file in the directory specified
  • If a file in the directory, is a file and matches with the name specified by user, add the file to coincidences list
  • If a file is a directory, search inside all the files/directories inside it with the same logic explained above
• If the coincidences list has files, show to user the path where those files resides

To ask the user the data we use the class Console that let us to get data from user input like this:

SCJP: Using File object (Part 1)

Right now i'm reading a little bit about some key classes of java.io package because is one of the SCJP topics, and y want to share with you some concepts about using File objects and doing operations with them.

First of all, File is not an object used to read or write information in files, it's more complex than that, it 's purpose is provide us an abstract representation of a file or directory and do file/directory special stuff like renaming, creating, deleting files and/or directories. If you wanna write or read file contents you should use Readers or Writers classes that have special methods to read lines of files, write lines and so on, those classes uses File objects to do those things, but that will be discused on another post.

As i said before, you can do operations like renaming files, deleting files, creating files and so on. But before that, let's view how to initialize a simple File object. The simplest way to do that is the next:

File myFile = new File("nameOfMyFile.txt");

As you can see, you initialize it passing the name of the file. Notice that we haven't specified something like the directory where file resides or even don't know if the file already exists!! First: when you create a File object, you hadn't created any file...yet, and, you can create File objects to represent new files (that will be created) or to represent existing files. If you want to create a file, you use the function createNewFile(), that returns a boolean, when is true, the file was created, else the file wasn't created. You can get false if for example,  if the file already exists.

File myFile = new File("nameOfMyFile.txt");
try {
    myFile.createNewFile();
    }catch(IOException ex){ex.printStackTrace();}

As you can see, this method can throw an IOException so we have to handle it or declare it in the method. The question here is: Where is created the file? Well, the base directory is the directory where resides the jar file or the .class file. If you want to check if an existing file exists, you simply use the method exists() XD , suppose this: In the .class directory exists a file named someFile.txt and you want to verify it's existence, so, you have to do this: