java

The Dart ternary operator syntax (examples) alvin September 21, 2019 - 2:48pm

As a quick note, the Dart ternary operator syntax is the same as the Java ternary operator syntax. The general syntax is:

result = testCondition ? trueValue : falseValue

A few examples helps to demonstrate Dart’s ternary syntax:

Notes on how to use GraalVM profile-guided optimizations alvin July 30, 2019 - 3:05pm

As a brief note today, I found that GraalVM was actually making one of my Scala/Java/JVM applications slower, so with the help of Thomas Wuerthinger at Oracle, I learned a little bit about how to use the GraalVM profile-guided optimizations.

Five good ways (and two bad ways) to read large text files with Scala alvin July 28, 2019 - 5:58pm

I’m working on a small project to parse large Apache access log files, with the file this week weighing in at 9.2 GB and 33,444,922 lines. So I gave myself 90 minutes to try a few different ways to write a simple “line count” program in Scala. (Not my final goal, but something I could use to measure file-reading speed without applying my algorithm.)

A `printf` format reference page (cheat sheet)

Summary: This page is a printf formatting cheat sheet. I originally created this cheat sheet for my own purposes, and then thought I would share it here.

A great thing about the printf formatting syntax is that the format specifiers you can use are very similar — if not identical — between different languages, including C, C++, Java, Perl, PHP, Ruby, Scala, and others. This means that your printf knowledge is reusable, which is a good thing.

GraalVM native executables can run faster than Scala/Java/JVM applications, with much less memory consumption

In two small tests where GraalVM was able to create a native executable, the native executable ran significantly faster than the equivalent Scala/Java code running with the Java 8 JVM, and also reduced RAM consumption by a whopping 98% in a long-running example. On the negative side, GraalVM currently doesn’t seem to work with Swing applications.

Notes on looking at MacOS application/process memory usage

Very briefly, I spent a little time today trying to understand how much memory/RAM a Java/Swing application was really using, and these are my notes from that excursion. Note that the app is bundled as a MacOS/Java app I named AlPad, but from some system perspectives it is only seen by the name JavaAppLauncher. Here are my notes, which will hopefully be useful to me in the future:

How to fire MacOS notifications with AppleScript and Scala

Table of Contents1 - A “Hello, world” MacOS AppleScript notification2 - AppleScript: Mac notification with a sound3 - How to add a title and subtitle to your notification4 - Running from Scala (or Java)5 - See also6 - Summary

Summary: This tutorial demonstrates how to fire MacOS system notifications with AppleScript and Scala (or Java).

In this article it helps if you already know a little bit about AppleScript, though that’s not completely necessary. Near the end of the tutorial I show how to invoke the AppleScript code using Scala, so feel free to skip down to there if you just want to see that — you can always read the stuff at the top for reference later.

A Java method that returns a random boolean value based on a probability

If you ever need a Java method that returns a boolean value based on a given probability, I can confirm that this method works:

/**
 * `probability` should be given as a percentage, such as
 * 10.0 (10.0%) or 25.5 (25.5%). As an example, if `probability` 
 * is 60% (60.0), 100 calls to this function should return ~60 
 * `true` values.
 * (Note that Math.random returns a value >= 0.0 and < 1.0.)
 */
static boolean getRandomBoolean(float probability) {
    double randomValue = Math.random()*100;  //0.0 to 99.9
    return randomValue <= probability;
}

How to sort data that’s in a Java HashMap (using a TreeMap)

Here’s a brief example of how to sort data that’s already in a Java HashMap. First, some HashMap data:

import java.util.*;

Map<Integer, Float> playMap = new HashMap<Integer, Float>() {{
    put(10,  1f);
    put(12,  2f);
    put(15,  4f);
    put(18,  6f);
    put(20,  6f);
    put(25,  7f);
    put(30,  6f);
    put(35,  5f);
    put(40,  5f);
}};

A HashMap won’t keep that data in sorted order, so if you want your data sorted, one way to sort it is to add the elements to a Java TreeMap: