Sekai 🌐 🗺

Sekai (世界) is the kanji for “the world”. That’s a great word because of the scale that it designates.

Passed Codingame Java Certification Test

A note to some forgotten methods

 Posted on April 20, 2023  |  1 min  |  Vincent Tam  |   0 comment

String regex replace using capture groups

Since Java SE 9, java.util.regex.Matcher’s replaceAll() method supports lambda expressions.

// import java.util.regex.*;
String varName = "random_string";
Pattern pattern = Pattern.compile("_([a-z])");
Matcher matcher = pattern.matcher(varName);
String result = matcher.replaceAll(m -> m.group(1).toUpperCase());

Source: Arvind Kumar Avinash’s answer on Stack Overflow

Check characters properties using Character’s static methods

The Character class provides some static predicates like

  • isAlphabetic(char c)
  • isDigit(char c)
  • isLowerCase(char c)

Source: Java Character isAlphabetic() Method on Javapoint

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Java  Codingame 

Fixed Archetype Error for This Site

 Posted on April 11, 2023  |  2 min  |  Vincent Tam  |   0 comment

Background

In Customized Archetype for This Site, I was using

{{ slicestr .Name 11 | humanize | title }}

in the title attribute in my site’s archetypes/default.md, so that the first 11 characters (YYYY-MM-DD-) would be taken out if I type this command.

$ hugo new post/$(date -I)-<MY_POST_TITLE>.md

In practice, <MY_POST_TITLE> can be replaced to any title, like my-post-title.

Problem

I wanted to create my IntelliJ cheatsheet, so I typed this command.

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Hugo 

Exploration of My First IntelliJ Project

 Posted on April 5, 2023  |  5 min  |  Vincent Tam  |   0 comment

We’ll try to stay in the project root if possible.

Find all non-hidden files to know the file structure.

$ find -path './.*' -prune -o -type f -print
./Algo-init.iml
./out/production/Algo-init/fr/eql/ai114/algo/init/demo/_1_HelloWorld.class
./src/fr/eql/ai114/algo/init/demo/_1_HelloWorld.java

  • -prune returns true for the chosen path and prevents find from descending.

  • -o means OR, so the paths matching -prune won’t pass through -o.

  • -type f selects files, not folders.

  • By default, AND is used to connect different conditions.

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Linux  IntelliJ 

Reuse Commands with Shell Arguments

My arguments for arguments, functions and alias

 Posted on March 25, 2023  (Last modified on April 13, 2023)  |  2 min  |  Vincent Tam  |   0 comment

Background

We often want to test the output with different values for a parameter. Here’s an example: we have a parameter that pandoc icon pandoc uses to / compile source code files to PDF / M$ Word / etc.

rm output.html; param=0; pandoc input$param.txt -o output.html; \
echo param = $param

In practice, a parameter can be a font, the font size, etc, and there can be multiple parameters.

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linux  tcsh 

Finding Pandoc Logo

 Posted on March 24, 2023  |  1 min  |  Vincent Tam  |   0 comment

Background

I’m writing my guide for preparing simple documents. I hope that users can prepare documents efficiently and the prepared documents look smart.

Problem

To help readers get my message in the linked guide, I used many icons from Font Awesome. However, it doesn’t include pandoc’s logo. I tried searching that using the search string “pandoc logo filetype:svg”. Duckduckgo couldn’t find any results. Luckily, Google found many SVGs. The first result linked to a relevant discussion on Google Groups. However, all posts were collapsed, and the desired SVG didn’t show up.

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pandoc  SVG 

Some Public APIs to Be Viewed

 Posted on March 16, 2023  (Last modified on April 17, 2023)  |  1 min  |  Vincent Tam  |   0 comment

API description
JSON Placeholder mock REST APIs for development only
Google Translate generate free translations up to a certain limit
Open Weather Map weather prediction across the world
REST Countries info about the world’s countries
IP API data about IP addresses
Random Data API like the first one, but with a sharper focus on random data
Pokemon API info about Pokemon with recent introduction of GraphQL API
API  useful sites 

Merge Two PDF to Single Encrypted PDF

 Posted on March 15, 2023  (Last modified on August 19, 2025)  |  1 min  |  Vincent Tam  |   0 comment

Problem

I have unprotected

  1. input1.pdf
  2. input2.pdf

and I want to create one single encrypted.pdf.

My try

I looked up QPDF’s manual and tried the following command.

qpdf --empty --pages input{1,2}.pdf --encrypt upw opw 256 -- encrypted.pdf

but I got this error.

qpdf: unrecognized argument --encrypt (pages options must be terminated with --)

For help:
  qpdf --help=usage       usage information
  qpdf --help=topic       help on a topic
  qpdf --help=--option    help on an option
  qpdf --help             general help and a topic list

Solution

The sentence inside the parentheses says it all.

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PDF  QPDF