Skip to main content

Compiling and Executing Java Files With -cp

I decided I was going to "man up" and figure out how to compile a java program with an external dependency from the command line instead of relying on an IDE-- the DOS command line, to be more specific.

I ran into a few problems:

1.  The external dependency was given to me as a java file.  I experimented compiling it as a .jar, but I wasn't sure how to import a class from a .jar, so I ended up compiling it into a class.

2.  When I tried to run the file, I got an error saying that the class had been compiled with a different version of Java than my JRE.  The Internet told me to check my path variable for Java.  It sure looked like it was pointing to the latest JRE (and the same version of Java as my compiler).  I asked the Internet again and found the following command:

for %I in (java.exe) do @echo %~$PATH:I

I'm not exactly sure what the syntax of that magic command is (intuitively it's returning the path that executes when I run the "java" command), but it was certainly revealing: I had some old system level install of Java that I'd done before I installed the most recent JDK.  I removed that old install, and the error went away.

3.  I was able to compile the java program and feed it the correct path for the library -- but when I tried to run it, I needed to feed it the path for the library again and I couldn't figure out how to do it.  I knew it involved the -cp argument.  I thought I was just supposed to give it the path to the dependency.  After a lot of experimenting, I realized I didn't understand exactly what -cp does (what the classpath is in Java).  So I looked it up, and as far as I can tell now, the classpath is where Java looks for classes (duh).  So if I have a dependency class in one directory and a main class in another directory, I have to give Java two classpaths.  The way to do that -- add a semicolon:

java -cp <path to directory where the library is>;<path to directory where the main class is> <main class>

or in my case

java -cp libraries;out\production\AlgorithmsChapter1 Drawing

So what this says is run a java program called Drawing and look for classes in libraries (where the dependency is) and in out\production\AlgorithmsChapter1.

***

I should know all of these things before I start fumbling around writing Java programs.  But it's still worth learning -- even if I have to learn it the hard way.

Comments

Post a Comment

Popular posts from this blog

Getting Geodata From Google's API

The apps I'm going to be analyzing are part of Dr. Charles Severance's MOOC on Python and Databases and work together according to the following structure (which applies both in this specific case and more generally to any application that creates and interprets a database using online data). The data source, in this case, is Google's Google Maps Geocoding API.  The "package" has two components: geoload.py  and geodump.py .  geoload.py  reads a list of locations from a file -- addresses for which we would like geographical information -- requests information about them from Google, and stores the information on a database ( geodata.db ).  geodump.py  reads and parses data from the database in JSON, then loads that into a javascript file.  The javascript is then used to create a web page on which the data is visualized as a series of points on the world-map.  Dr. Severance's course focuses on Python, so I'm only going to work my way through ...
Post a Comment
Read more

The Jump Algorithm

Meetup Went to a Coding Whiteboard Meetup tonight.  It was pretty great.  One of the leaders was even a CS master's student.  At first, honestly, I felt a little bit frustrated, especially because everyone around me seemed to be using pretty high level concepts / approaches that I wasn't familiar with.  But I found someone and relentlessly talked him through his approach until we both kind of realized there were issues in the problem we hadn't worked out yet.  I guess it just reinforces my feeling that when something seems too difficult, if you can, you need to find someone and force him to explain it to you in terms you can understand.  If the people around you really understand what they're about, they will have no problem and you'll learn a lot (assuming they're patient, I guess).  If they don't, you'll realize you aren't as alone as you thought you were.  Bit of the old Socrates. Problem So imagine you have an array with a bunch of numbe...
Post a Comment
Read more

Shell Sort

Today I spent a little bit of time researching the "Shell" sort.  I wanted to post a few notes about the Princeton Algorithms Course's implementation to help me solidify my understanding. First, a little tidbit.  When I first heard about this algorithm, I thought it had something to do with shell games.  Turns out a man named Donald Shell discovered this method of sorting, whence the name. The Algorithms  book gives the following explanation (Sedgewick and Wayne,  Algorithms, 4th ed., p. 258): The idea is to rearrange the array to give it the property that taking every hth entry (starting anywhere) yields a sorted subsequence. Such an array is said to be h-sorted. Put another way, an h-sorted array is h independent sorted subsequences, interleaved together. By h-sorting for some large values of h, we can move items in the array long distances and thus make it easier to h-sort for smaller values of h. Using such a procedure for any sequence of values o...
Post a Comment
Read more