Yes java.io.File; it's a pretty easy class to work with.
I find myself always having to use a method from that class.
There are three constructors:
public File(String pathname);
public File(String parent, String child);
public File(File parent, String child);
And a host of methods. Here are the ones i use the most.
public boolean isFile();
public String getName();
public String getPath();
public boolean createNewFile();
public boolean delete();
public boolean deleteOnExit();
public long length();
public boolean mkdir();
public boolean mkdirs();
public boolean renameTo(File dest);
public File[] listFiles();
public File[] listFiles(FilenameFilter filter);
public File[] listFiles(java.io.FileFilter filter);
public String[] list();
public String[] list(FilenameFilter filter);
public static File createTempFile(String prefix, String suffix);
public static File createTempFile(String prefix, String suffix File directory);
These methods usually come in handy when i need a temporary place to store data that i might need at a later time in my program. Use deleteOnExit() to request that the files be deleted when the Java VM exits normally.