Java

Version switching across platforms

Java version management is a pain. These utilities make it tolerable across macOS, Arch, and Debian.

Quick Switching

Alias	Command	Description
java8	setjdk 8	Switch to Java 8
java11	setjdk 11	Switch to Java 11
java17	setjdk 17	Switch to Java 17
java21	setjdk 21	Switch to Java 21
javalist	List versions	Show all available

One command to switch Java versions. Works on macOS, Arch Linux, and Debian/Ubuntu.

Functions

setjdk — Switch Version

Platform-aware Java version switching:

setjdk 17
# Sets JAVA_HOME
# Updates PATH
# Works on macOS, Arch, Debian

Check with java -version after switching.

list_java_versions — Available Versions

See what's installed:

javalist
# Shows all installed JDK versions
# Platform-specific output

Platform-Specific Details

macOS

Uses /usr/libexec/java_home for version management:

# List all Java versions
/usr/libexec/java_home -V

# Get path for specific version
/usr/libexec/java_home -v 17

# The setjdk function handles this automatically

Install Java versions with Homebrew:

brew install openjdk@17
brew install openjdk@21

Arch Linux

Uses archlinux-java utility:

# Show available versions
archlinux-java status

# Switch (requires sudo)
sudo archlinux-java set java-17-openjdk

# The setjdk function handles this automatically

Install Java with pacman:

sudo pacman -S jdk17-openjdk
sudo pacman -S jdk21-openjdk

Debian/Ubuntu

Uses update-java-alternatives:

# List available versions
update-java-alternatives -l

# Switch (requires sudo)
sudo update-java-alternatives -s java-17-openjdk-amd64

# The setjdk function handles this automatically

Install Java with apt:

sudo apt install openjdk-17-jdk
sudo apt install openjdk-21-jdk

Gradle Integration

Gradle-specific utilities are in sh/gradle.sh:

Function	Description
gtest	Run Gradle tests
grun	Run Gradle task
gclear	Clean Gradle caches
gdeps	Show dependencies
gbuild	Build module
gtasks	List available tasks

These work with the Gradle wrapper (./gradlew).

Workflows

Check Current Version

# See active Java version
java -version

# See JAVA_HOME
echo $JAVA_HOME

# List all available
javalist

Switch for a Project

# Enter project
cd ~/projects/legacy-app

# Check what's available
javalist

# Switch to required version
java11  # or: setjdk 11

# Verify
java -version

# Build
./gradlew build

Gradle Build

# Ensure correct Java version
java17

# Clean build
./gradlew clean build

# Run tests
./gradlew test

# Or with functions:
gbuild
gtest

Managing Multiple Projects

# Project A needs Java 11
cd ~/projects/project-a
java11
./gradlew build

# Project B needs Java 17
cd ~/projects/project-b
java17
./gradlew build

Consider adding a .java-version file to projects and auto-switching on cd (similar to .nvmrc for Node).

Troubleshooting

JAVA_HOME Not Set

# Check current value
echo $JAVA_HOME

# If empty, use setjdk
setjdk 17

# Verify
echo $JAVA_HOME

Wrong Version Active

# Check current
java -version

# See what's available
javalist

# Switch to correct one
setjdk 17

Gradle Using Wrong Java

# Gradle uses JAVA_HOME
# Switch Java first
java17

# Then run Gradle
./gradlew build

# Or specify explicitly
JAVA_HOME=/path/to/jdk17 ./gradlew build

Pro Tips

One version per project: Different projects need different Java versions. Get comfortable switching.

macOS Homebrew: Use brew install openjdk@<version> for easy management.

LTS versions: Stick to LTS releases (11, 17, 21) unless you need specific features.

Gradle wrapper: Always use ./gradlew instead of global gradle. Ensures consistent builds.

JAVA_HOME in scripts: Shell scripts should check JAVA_HOME. Use setjdk before running them.

Auto-switch on cd: Consider adding project-specific Java version detection to your shell (like NVM's auto-switch).

Keep it simple: Don't install every Java version. Install what you actually use—usually just one or two.