Credo che intanto ti debba studiare la classe File e i suoi metodi tanto utili.
Ti mando un po di codice d'esempio:
Es 1:
codice:
import java.io.File;

/**
 *Questo esempio verifica l'esistenza di un file
 * @author mau2
 */
public class TryFile {
   
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // Creazione di un oggetto che e' una directory
        String parent = new File(System.getProperty("java.home")).getParent();
        File myDir = new File(parent,
                File.separator + "src" + File.separator + "java" + File.separator + "io");
        System.out.println(myDir + (myDir.isDirectory() ? " is" : " is not") +
                " a directory");
        
        //creazione di un oggetto che e' un file
        File myFile = new File(myDir, "File.java");
        System.out.println(myFile + (myFile.exists() ? " does" : " does not") +
                " exist");
        
        System.out.println(myFile + (myFile.isFile() ? " is" : " is not") +
                " a file");
        
        System.out.println(myFile + (myFile.isHidden() ? " is" : " is not") +
                " hidden");
        
        System.out.println("You can" + (myFile.canRead() ? " " : "not ") +
                "read " + myFile);
        
        System.out.println("You can" + (myFile.canWrite() ? " " : "not ") +
                "write " + myFile);
        
        System.out.println( );
    }
    
}
es2 :
codice:
public class TryFile2 {
    
    
    /**Ottieni ulteriori informazioni
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // Creazione di un oggetto che e' una directory
        String parent = new File(System.getProperty("java.home")).getParent();
        File myDir = new File(parent,
                 "src" + File.separator + "java" + File.separator + "io");
        
        System.out.println(myDir.getAbsolutePath()
        + (myDir.isDirectory() ? " is " : " is not ")
        + "a directory");
        System.out.println("The parent of " + myDir.getName() + " is "
                + myDir.getParent());
        
        // Get the contents of the directory
        File[] contents = myDir.listFiles();
        
        // List the contents of the directory
        if (contents != null) {
            System.out.println("\nThe " + contents.length
                    + " items in the directory " + myDir.getName()
                    + " are:");
            for (int i = 0; i < contents.length; i++) {
                System.out
                        .println(contents[i] + " is a "
                        + (contents[i].isDirectory() ? "directory" : "file")
                        + " last modified "
                        + new Date(contents[i].lastModified()));
            }
        } else {
            System.out.println(myDir.getName() + " is not a directory");
        }
        
        
        
        
    }
    
    
}