Java

JDK tools and runtime commands. Compile, run, package, and debug Java applications from the command line.

45 commands

Browse by Topic

Getting Started

Quick setup and installation

3commands

Compiler

javac compilation

8commands

Runtime

java execution

9commands

JAR

JAR file management

8commands

Tools

jlink, jpackage, javadoc

8commands

Diagnostics

jcmd, jps, jstat

9commands

Install Java (macOS)

$ brew install openjdk

Install OpenJDK using Homebrew on macOS

Check Java version

$ java --version

Display the installed Java runtime version

Compile a Java file

$ javac Main.java

Compile a Java source file into bytecode

Compile Java file

$ javac MyClass.java

Compile a single Java source file.

Compile with classpath

$ javac -cp lib/*:. MyClass.java

Compile with external JARs in the classpath.

Compile to output directory

$ javac -d target/classes src/*.java

Compile sources and output class files to a directory.

Compile with all warnings

$ javac -Xlint:all MyClass.java

Enable all compiler warnings for better code quality.

Compile for specific version

$ javac --release 17 MyClass.java

Compile targeting a specific Java version.

Compile with debugging info

$ javac -g MyClass.java

Include debugging information in class files.

Compile module

$ javac -d out --module-source-path src $(find src -name '*.java')

Compile Java modules from source path.

Show deprecation warnings

$ javac -deprecation MyClass.java

Show detailed deprecation warnings during compilation.

Run Java class

$ java MyClass

Run a compiled Java class with main method.

Run with classpath

$ java -cp lib/*:target/classes com.example.Main

Run with specified classpath including JARs.

Set heap memory

$ java -Xms512m -Xmx4g MyApp

Set initial (512MB) and max (4GB) heap memory.

Use G1 garbage collector

$ java -XX:+UseG1GC MyApp

Run with G1 garbage collector for balanced performance.

Enable heap dump on OOM

$ java -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/tmp MyApp

Automatically create heap dump when OutOfMemoryError occurs.

Set system property

$ java -Dconfig.file=/path/to/config.yml MyApp

Pass system property to the application.

Enable GC logging

$ java -Xlog:gc*:file=gc.log:time,level,tags MyApp

Log garbage collection events to file (Java 9+).

Run single-file source

$ java MyScript.java

Compile and run single-file program directly (Java 11+).

Use ZGC collector

$ java -XX:+UseZGC -Xmx16g MyApp

Use ZGC for low-latency large heap applications.

Create JAR file

$ jar --create --file app.jar -C classes .

Create a JAR from compiled classes directory.

Create executable JAR

$ jar --create --file app.jar --main-class com.example.Main -C classes .

Create JAR with entry point for direct execution.

Run JAR file

$ java -jar app.jar

Execute a JAR file with Main-Class manifest entry.

Extract JAR contents

$ jar --extract --file app.jar

Extract all contents from a JAR file.

List JAR contents

$ jar --list --file app.jar

List all files contained in a JAR.

View manifest

$ unzip -p app.jar META-INF/MANIFEST.MF

Display the manifest file from a JAR.

Update JAR contents

$ jar --update --file app.jar -C updated-classes .

Add or update files in an existing JAR.

Describe module JAR

$ jar --describe-module --file module.jar

Show module descriptor information for a modular JAR.

Create runtime image (jlink)

$ jlink --module-path $JAVA_HOME/jmods:mods --add-modules com.myapp --output runtime

Create custom minimal JRE with only required modules.

Optimized runtime image

$ jlink --strip-debug --compress=2 --no-header-files --no-man-pages --add-modules java.base --output minimal-jre

Create minimal runtime with optimizations (~25MB).

Create native installer (jpackage)

$ jpackage --input lib --main-jar app.jar --main-class com.example.Main --name MyApp --type dmg

Create native installer (.msi, .dmg, .deb) for distribution.

Generate Javadoc

$ javadoc -d docs -sourcepath src -subpackages com.example

Generate HTML API documentation from source code.

List trusted CA certs

$ keytool -list -cacerts

List all trusted CA certificates in the JDK keystore.

Generate keystore

$ keytool -genkeypair -alias mykey -keyalg RSA -keysize 2048 -keystore keystore.jks

Generate a new key pair and self-signed certificate.

Analyze dependencies (jdeps)

$ jdeps --multi-release 17 app.jar

Analyze class and package dependencies of a JAR.

List JDK modules

$ java --list-modules

Display all modules available in the JDK.

List Java processes

$ jps -lv

List all running Java processes with full details.

Get JVM flags

$ jcmd <pid> VM.flags

Display all JVM flags including defaults for a process.

Thread dump

$ jcmd <pid> Thread.print

Generate thread dump to analyze deadlocks and thread states.

Heap dump

$ jcmd <pid> GC.heap_dump /tmp/heap.hprof

Create heap dump for memory analysis.

Monitor GC activity

$ jstat -gc <pid> 1000

Display GC statistics every second.

Start flight recording

$ jcmd <pid> JFR.start duration=60s filename=recording.jfr

Start Java Flight Recorder for low-overhead profiling.

Heap histogram

$ jcmd <pid> GC.class_histogram

Show memory usage by class (live object counts).

Force garbage collection

$ jcmd <pid> GC.run

Trigger full garbage collection (use sparingly).

Native memory tracking

$ jcmd <pid> VM.native_memory summary

Show native memory usage (requires -XX:NativeMemoryTracking=summary).

Discussion

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Java

JDK tools and runtime commands. Compile, run, package, and debug Java applications from the command line.

45 commands

Browse by Topic

Getting Started

Quick setup and installation

3commands

Compiler

javac compilation

8commands

Runtime

java execution

9commands

JAR

JAR file management

8commands

Tools

jlink, jpackage, javadoc

8commands

Diagnostics

jcmd, jps, jstat

9commands

Install Java (macOS)

$ brew install openjdk

Install OpenJDK using Homebrew on macOS

Check Java version

$ java --version

Display the installed Java runtime version

Compile a Java file

$ javac Main.java

Compile a Java source file into bytecode

Compile Java file

$ javac MyClass.java

Compile a single Java source file.

Compile with classpath

$ javac -cp lib/*:. MyClass.java

Compile with external JARs in the classpath.

Compile to output directory

$ javac -d target/classes src/*.java

Compile sources and output class files to a directory.

Compile with all warnings

$ javac -Xlint:all MyClass.java

Enable all compiler warnings for better code quality.

Compile for specific version

$ javac --release 17 MyClass.java

Compile targeting a specific Java version.

Compile with debugging info

$ javac -g MyClass.java

Include debugging information in class files.

Compile module

$ javac -d out --module-source-path src $(find src -name '*.java')

Compile Java modules from source path.

Show deprecation warnings

$ javac -deprecation MyClass.java

Show detailed deprecation warnings during compilation.

Run Java class

$ java MyClass

Run a compiled Java class with main method.

Run with classpath

$ java -cp lib/*:target/classes com.example.Main

Run with specified classpath including JARs.

Set heap memory

$ java -Xms512m -Xmx4g MyApp

Set initial (512MB) and max (4GB) heap memory.

Use G1 garbage collector

$ java -XX:+UseG1GC MyApp

Run with G1 garbage collector for balanced performance.

Enable heap dump on OOM

$ java -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/tmp MyApp

Automatically create heap dump when OutOfMemoryError occurs.

Set system property

$ java -Dconfig.file=/path/to/config.yml MyApp

Pass system property to the application.

Enable GC logging

$ java -Xlog:gc*:file=gc.log:time,level,tags MyApp

Log garbage collection events to file (Java 9+).

Run single-file source

$ java MyScript.java

Compile and run single-file program directly (Java 11+).

Use ZGC collector

$ java -XX:+UseZGC -Xmx16g MyApp

Use ZGC for low-latency large heap applications.

Create JAR file

$ jar --create --file app.jar -C classes .

Create a JAR from compiled classes directory.

Create executable JAR

$ jar --create --file app.jar --main-class com.example.Main -C classes .

Create JAR with entry point for direct execution.

Run JAR file

$ java -jar app.jar

Execute a JAR file with Main-Class manifest entry.

Extract JAR contents

$ jar --extract --file app.jar

Extract all contents from a JAR file.

List JAR contents

$ jar --list --file app.jar

List all files contained in a JAR.

View manifest

$ unzip -p app.jar META-INF/MANIFEST.MF

Display the manifest file from a JAR.

Update JAR contents

$ jar --update --file app.jar -C updated-classes .

Add or update files in an existing JAR.

Describe module JAR

$ jar --describe-module --file module.jar

Show module descriptor information for a modular JAR.

Create runtime image (jlink)

$ jlink --module-path $JAVA_HOME/jmods:mods --add-modules com.myapp --output runtime

Create custom minimal JRE with only required modules.

Optimized runtime image

$ jlink --strip-debug --compress=2 --no-header-files --no-man-pages --add-modules java.base --output minimal-jre

Create minimal runtime with optimizations (~25MB).

Create native installer (jpackage)

$ jpackage --input lib --main-jar app.jar --main-class com.example.Main --name MyApp --type dmg

Create native installer (.msi, .dmg, .deb) for distribution.

Generate Javadoc

$ javadoc -d docs -sourcepath src -subpackages com.example

Generate HTML API documentation from source code.

List trusted CA certs

$ keytool -list -cacerts

List all trusted CA certificates in the JDK keystore.

Generate keystore

$ keytool -genkeypair -alias mykey -keyalg RSA -keysize 2048 -keystore keystore.jks

Generate a new key pair and self-signed certificate.

Analyze dependencies (jdeps)

$ jdeps --multi-release 17 app.jar

Analyze class and package dependencies of a JAR.

List JDK modules

$ java --list-modules

Display all modules available in the JDK.

List Java processes

$ jps -lv

List all running Java processes with full details.

Get JVM flags

$ jcmd <pid> VM.flags

Display all JVM flags including defaults for a process.

Thread dump

$ jcmd <pid> Thread.print

Generate thread dump to analyze deadlocks and thread states.

Heap dump

$ jcmd <pid> GC.heap_dump /tmp/heap.hprof

Create heap dump for memory analysis.

Monitor GC activity

$ jstat -gc <pid> 1000

Display GC statistics every second.

Start flight recording

$ jcmd <pid> JFR.start duration=60s filename=recording.jfr

Start Java Flight Recorder for low-overhead profiling.

Heap histogram

$ jcmd <pid> GC.class_histogram

Show memory usage by class (live object counts).

Force garbage collection

$ jcmd <pid> GC.run

Trigger full garbage collection (use sparingly).

Native memory tracking

$ jcmd <pid> VM.native_memory summary

Show native memory usage (requires -XX:NativeMemoryTracking=summary).

Discussion

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