Scala, Java, Unix, MacOS tutorials (page 103)

XO Play is a “thinking man’s” football game that I created for Android devices. It’s for those of us who enjoy thinking about football strategy, of how to take advantage of our strengths and our opponents’ weaknesses, and how to call plays to win games. If you’ve ever watched a football game and thought, “I can call plays better than this guy,” XO Play is for you.

Version 1.4

Version 1.4 introduces four game levels you can choose from:

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;
}

Let me start by saying that I don’t know if I’m an “A” Player. In part, that definition depends (a) on what work I’m doing, and (b) who you compare me to. For instance, if you compare me to Linus Tourvalds as a Linux C programmer, I’m very clearly not an A Player. Shoot, I’m not even a player.

But if you were to judge me on other skills, I’d like to say that I’m at least a B Player in the things I care about. As I wrote in my book, A Survival Guide for New Consultants, my superpower as a programmer/analyst is empathy; I care about my work, and about my success and my client’s success. If you pay me $100,000 to do some work, I want you to make at least 2X or 10X or more from my work. I want my clients and sponsors to succeed.

Beyond that care, since I began paying attention to Apple and Jonathan Ive starting back around 2005, I’ve become more interested than ever in quality. When I work on something, I imagine that I’m either working with Mr. Ive, or that I’m going to have him review my work, and I want it to be impeccable.

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 14.4, “How to run a shell command from the Scala REPL.”

Problem

You want to be able to run a shell command from within the Scala REPL, such as listing the files in the current directory.

Solution

Run the command using the :sh REPL command, then print the output. The following example shows how to run the Unix ls -al command from within the REPL, and then show the results of the command:

As a little note today, if you ever need to extract a subset of a Java list or array, here are some examples of the Java subList method:

import java.util.*;

public class SubList {

    public static void main(String[] args) {

        List<String> x = new ArrayList<>();
        x.add("a");
        x.add("b");
        x.add("c");
        x.add("d");
        x.add("e");

        // `subList(int fromIndex, int toIndex)`
        // array indexes start at 0.
        // 1st arg is inclusive (included), 2nd arg is exclusive (not included).
        List a = x.subList(0,1);  // [a]
        List b = x.subList(0,2);  // [a, b]
        List c = x.subList(0,4);  // [a, b, c, d]      # same as `x.subList(0,x.size()-1)`
        List d = x.subList(0,5);  // [a, b, c, d, e]   # same as `x.subList(0,x.size())`
        List e = x.subList(0,6);  // IndexOutOfBoundsException
        List f = x.subList(1,1);  // f []
        List g = x.subList(1,2);  // g [b]
        List h = x.subList(2,5);  // h [c, d, e]
        
    }
}

If you print the results of each line you’ll see the results on the right side of the comments. As shown:

• The first element in a list or array is at index 0
• The toIndex is exclusive, meaning it won’t be included in the results
• If you go outside the size of the initial list, you’ll get an IndexOutOfBoundsException
• The original list isn’t modified; if you print x, you’ll see that it still includes all of the original elements

If you ever need to extract a subset of a Java list or array into another list or array, I hope these Java subList examples are helpful.