Java – Perceptual Gestalt

I’ve only ever heard bad things about Java so I have steered clear of it. But, I will tell you one thing, Java’s BigInteger is nice and easy and very powerful for calculations with very large numbers.

Now that I’m spending more time with Java, I wanted to jot down a few things that I’ve learned along the way.

What I like About Java

It’s an Object-Oriented Programming

While I can handle and adapt to a flat structure consisting primarily of variables passed around and functions that have to be created to extend functionality and called to process a selection of data, being object-oriented seems to keep things more modular, cleaner, and extensible. If given an opportunity to interact with OOP I won’t shy away from it.

Low Effort Requirement to Get a Program Up and Running

If I need to whip something up, I’ll use either Python, Bash, or Java. If I want to perform simple admin tasks, Bash works just fine. If I need to perform somewhat more complex HTTP/S requests, Python works well. If I need more complex structures and decent performance, Java can let you put things together rather quickly.

Command Line Arguments

Still parsing this information myself. Looks like I ought to try JCommander

Importing Packages

You may run into this when you’re working on a Java project:

SmallProjectThree.java:8: error: package org.bouncycastle.math.ec does not exist

This means your environment is not familiar with a package called bouncycastle.math.ec. The reason this error is thrown is because I am attempting to do some Elliptic-curve calculations and am using a snippet from im-infamou5 on GitHub.com

In general, to use a non-standard library, you need to find the *.jar file yourself, download it, and drop it in your CLASSPATH (if this doesn’t exist or you want to redefine it, you can do so; see -cp below)

Specific to Bouncy Castle, these are the steps I took.

Download the .jar file from the org’s download page directly. Now, there are a ton of options available to you on that page.
1. Trust but verify. I recommend using signed jar files so you can digitally trust the source. Once the package has been downloaded check the sha hash.
2. What JDK is installed on your system? Your system probably has Java installed (java -version) but the JDK is separate. Only one Java can exist but several JDKs can exist (in a given environment at a time). I am currently running Java build 13.0.2+8 and have 13.0.3 and 1.8.0_241 JDK present on my system. I am downloading JDK 14 and dropping it into the same directory.
  1. ```
  $ java -version
  java version "13.0.2" 2020-01-14
  Java(TM) SE Runtime Environment (build 13.0.2+8)
  Java HotSpot(TM) 64-Bit Server VM (build 13.0.2+8, mixed mode, sharing)
```
2. ```
$ pwd
/System/Volumes/Data/Library/Java/JavaVirtualMachines
$ ls
jdk-13.0.2.jdk jdk-14.jdk jdk1.8.0_241.jdk
```
3. Which .jar file do you need? I looked through the documentation and found that the “provider” had the math.ec library so I need the “provider” .jar
Add the *.jar file to my project’s directory tree.
1. Download it to the same directory that contains my SmallProject3.java program.
Compile my program using -cp or --classpath

$ javac -cp ./org/bouncycastle/bcprov-jdk14-164.jar SmallProjectThree.java

MAKEFILE

An expert in neither Java nor Make dropped this off.

JAVAC=javac
JAVA=java
sources = $(wildcard *.java)
classes = $(sources:.java=.class)

all : $(classes)

run : all
    $(JAVA) PrimitiveRoots

clean :
    rm -f *.class

%.class : %.java
    $(JAVAC) $<