Tag Archives: devnexus

DevNexus 2018 – Modules in Action

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Title: Modules in Action
Speakers: Mark Reinhold

For more blog posts, see the DevNexus 2018 live blogging table of contents

Demo used Java 10 RC.

Using JShell to look at modules

  • “foo”.getClass().getModule() – module java.base
  • “foo”.getClass().getModule().getClass() – class java.lang.Module
  • new java.sql.Timestamp(0).getModule() – module java.sql

Modules

  • java –list-modules – ex: java.sql@10
  • There are 75 modules in Open JDK 10

JavaDoc

  • The Java 9 JavaDoc shows modules on the home page instead of all the packages.
  • Clicking a module shows you the packages in the module.
  • Java 9 JavaDoc has search box

Random facts

  • tree – unix commands that list what is in directory and children (not installed by default)
  • Showed that can use * in classpath to get all files in lib directory. (since Java 6)

Creating a bare bones module

  • Create module-info.java file in root of src folder
  • Simplest module file is one line: module moduleName { }
  • If run javap against the class file, you can see “requires java.base;” was added. This is like a constructor calling super(). It is mandatory so you don’t need to type it.
  • jar –file x.jar –describe-module – shows name of file, requires and the package contained
  • java –module-path lib -m moduleName/className – run the program
  • java -classpath jar className – can still run a modular jar on the classpath
  • jar –create –file x.jar –main-class class -C classes – create a jar that can run without specifying the class to run
  • java –modulepath lib -m moduleName – run the program without specifying it by name

Refactoring the module to split into two

  • module module1 { requires packageName; }
  • module module2 { exports packageName; }

Problems

  • If remove module2 and try to run, get java.lang.module.FindException on startup since can’t find module. Error inlcudes “Error occurred during initialization of boot layer”
  • If forgot to type “requires”, and compile get “package x is not visible”
  • If two modules require each other and compile, get “cyclic dependence involving package x”
  • If forget to type “exports” and compile, get “IllegalAccessError exception” along with long message about exporting

jlink

  • Optional Java linker
  • New directory jmods in JAVA_HOME.
  • Each module in the JDK has a file in jmods
  • JDK got a lot bigger with Java 9 because shipping two copies of each module – the main one and the jmods directory
  • jlink –module-path $JAVA_HOME.jmods –output jre –add-modules java.base – creates a JRE that is an order of magnitude smaller than the full one (44M vs 329B)
  • Can include your custom app into the image in addition to JDK
  • jlink –module-path $JAVA_HOME.jmods:lib –output jrePlusApp –add-modules java.base myCustomModule
  • jlink has a –compress flag to make file smaller
  • Not platform independent. Can cross link to create file for other operating system

Reflection

  • Want to make it so private really means private and final really means final. Vs reflection today.
  • Illegal reflective access – first time, get warning. The warning tells you how to enable more warnings. There probably are, but don’t want to blast you with them. Eventually, warning will turn into a hard error.
  • Not planning to disallow illegal reflective access until after Java 11.
  • Supplementing “exports”, is “open. It allows extra reflection

Inside a jmod

  • jmods are like a zip file with extra structure.
  • classes directory with all of the classes
  • conf directory for files in runtime image
  • include directory for jni header files
  • legal directory with licenses if any
  • bin directory for launchers
  • lib directory for native code

My take

I like the live demo approach along with the emphasis on both concepts and common problems. I also like that Mark left a lot of time for Q&A.

 

DevNexus 2018 – Gradle – the basics and beyond

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Title: Gradle – the Basics and Beyond
Speakers: Ken Kousen

For more blog posts, see the DevNexus 2018 live blogging table of contents

Install

  • requires Java 7+
  • Gradle 4.2.1+ supports Java 9
  • Gradle releases frequently but is very backward compatible
  • Just unzip and add to path
  • The complete distribute includes the samples. The sample sources are also available online.

General

  • Gradle is now much faster than Maven
  • gradle.com is the enterprise version which is built on top of open source gradle.org.
  • Gradle is mostly implemented in Java. Groovy is for the DSL.
  • Uses Ant behind the scenes as well
  • Groovy comes with Gradle. Don’t need to install Groovy separately
  • gretty is jetty for gradle; also contains tomcat

Docs

Future

  • Kotlin
    • Creating a Kotlin DSL for simple build files.
    • Kotlin is not replacing Groovy
    • Not yet at 1.0.0
    • Goal is better IDE integration
  • Generator
    • Looking at being able to generate projects on web project like Spring Boot has

gradlew

  • Recommend using gradlew. Checking in the file guarantees users are on version of gradle that you intended
  • Has effect of creating many gradle installs on your machine. Not that big.

Creating a project

  • Can generate new project or port basic pom files.
  • Use porting as a guide and then hand edit
  • Generate new project in current directory (make empty directory by hand first)
    • mkdir proj
    • cd proj
    • gradle init –type java-application (or java-library)
  • Files/directories in project
    • gradlew/gradlew.bat – wrapper script
    • gradle/wrapper – jar and properties
    • settings.gradle – lists multi project builds
    • gradle.properties – key/value pairs used by build
  • In home directory’x .gradle
  • wrapper/distx – the binarry/installs.

Daemon

  • Improves performance
  • Cache a lot of the JVM startup
  • For a few hours, same daemon used if using same version of gradle on every project.
  • Tip: turn off daemon on CI servers so every build is a clean build

Gradle file

  • repositories
    • can use jcenter or maven central.
    • or can specify a different one for any Maven or Ivy repo; like internal corporate one
    • can list multiple repos and searches in order
  • dependencies
    • ‘group:name:version’ – same concept as Maven GAV. Or can split into three sections. Ken likes the former better; either fine.
    • can write compile (‘g:n:v’) to specify fully. Groovy parens are optional except when they are not. The DSL can interpret without parens and easier to read.
    • New Java plugin has api/implementation to use as scope instead of compile.
    • compile files – lets you add files not in the classpath
    • compile fileTree – lets you add a directory not in the classpath
  • plugins
    • if registered on plugins.gradle.org, can list id and version numbers.
    • built in plugins (ex: java) don’t get a version number

Commands

  • gradle build -t – rebuilds and then sits idle until you change code. Like a rebuild loop
  • gradle build –dry-run – shows what would run (can use -m instead of –dry-run)
  • gradle -b… – use different build file name
  • gradle –stsatus – shows processes

Build scan

  • Starting Gradle 4.3, will prompt you if you haven’t accepted the license agreement and try to use.
  • It’s hosted at Gradle so sends some info out.
  • Gradle Enterprise does build scans in house

My take

Good structured intro/review. Happy that Ken changed the background to white when we were reading code. He also made the code sufficiently large. I didn’t even need my glasses. Go Ken! The only time I needed my classes was when he showed the manual which uses dark gray on a light gray background for the comments. I knew more of the basics than I realized. But good to have it gel better in my head! And I definitely learned things. Rushed at the end though and that was where most of the new stuff is. Glad I’m a New Yorker and can handle talking fast. Can’t type that fast though so stopped taking notes.

DevNexus 2018 – How to Hire Good Programmers

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Title: How to hire good programmers
Speakers: Jennifer Bland

For more blog posts, see the DevNexus 2018 live blogging table of contents

Propose: Stop doing at home programming challenges

Problems

  • We don’t write new projects from scratch all the time at work.
  • Standing up an environment/project from scratch isn’t representative.
  • Being given 90 minutes to do something doesn’t count setup time and then judging them on code
  • [there’s also the problem that you don’t know if someone else did it and that you are expecting them to spend a lot of time on it]
  • [I like http://collabedit.com/ for a short at home exercise so can do real time and watch]

Propose: Implement short coding exercises – 10 lines or less

  • Assume 90 minute interview [I have shorter interviews]
  • Break questions into four areas of 15 minute chunks each. Pick four technologies that you use. Ex: html/css, core javascript, node
  • Goal of each section is to determine level of knowledge person has on that topic
  • For each chunk, ask questions.
  • Type 1: Test knowledge – traditional question. ex: what is difference between x and y. Start asking basic questions and ramp up.
  • Type 2: Write code – give structure and write code to do simple task. Ex: write a selector. Then make question a step harder. And so forth. [these questions are easy. I guess the target is for an entry level or junior developer?]
  • Scoring – set points for different levels of answer to each question and require minimum score to hire.

Propose: Casual tech discussions

  • Propose spending 30 minutes on this section.
  • At lunch at a conference, know people’s names, employer, where they live, what tech stack they use, etc.
  • At an interview, can find opinion. Do they have an opinion. Are they passionate. [I do this]
  • Allows candidate to be open, show understanding of topic, etc.
  • Goal: learn how person will fit into company
  • Also open ended questions like what online resources use.
  • [I thought this was going to be about having lunch with the candidate vs asking questions that are opinions.]

Q&A

  • What steps are in interview process other than the 90 minute interview? Post job and view resumes. HR will talk to the person first. Then spend a day and interview 5-6 people in one day. Usually half are “nos.” Then 1-2 strongest candidates and maybe someone close. Bring back the top couple and bring them back to write more code. Maybe 12 exercises in an hour where there isn’t enough time to complete all of them with half more common. You can see which ones they picked to determine strengths. Can have an offer in a a week. [that sounds like it assumes everyone is free to come in on same day]
  • Have you ever tested interview process on current team? No. But comparing candidates to each other. [I tested some of my questions on some teammates to ensure they aren’t too hard]
  • Do you recommend having candidates pair with current employees? Haven’t tried.
  • How batch candidates? Run job ads for two weeks. Have people come in over a week. It’s the second level where they come with a day or two.
  • How mitigate against people who can’t write code? Asking them to write code. Testing how they problem solve too.

Note: she works for and R&D division of Black and Decker. I imagine that gives them overall stronger candidates.

My take

I definitely agree with not giving a 90 minute project to do at home. I agree with the concept of having people write small code and do that. In less than 10 minutes I can tell if the person knows basic Java and then get on to the harder parts of the interview including more of soft skills and interests. (I suppose that is equivalent since it is on area?] I view the basic coding question as a screen. if they fail, the interview ends, but success doesn’t mean hire. And I agree on asking open ended/opinion questions. I don’t think anyone hires based on a 90 minute take home test though; I imagine they use that as a screen like i use my < 10 minute question on the phone/collabedit.