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Tooling Beginner

Single-file execution

Run single-file Java programs directly without javac.

Tooling

Code Comparison

✕ Java 8

$ javac HelloWorld.java
$ java HelloWorld
// Two steps every time

✓ Java 11+

$ java HelloWorld.java
// Compiles and runs in one step
// Also works with shebangs:
#!/usr/bin/java --source 25

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Why the modern way wins

⚡

One command

java File.java compiles and runs in one step.

📝

Script-like

Add a shebang line to make .java files executable scripts.

🎓

Learning-friendly

Newcomers run code immediately without learning build tools.

Old Approach

Two-Step Compile

Modern Approach

Direct Launch

Since JDK

Difficulty

Beginner

JDK Support

Single-file execution

Available

Widely available since JDK 11 (Sept 2018)

How it works

The Java launcher can compile and run a single source file in one command. Combined with shebang support on Unix, Java files can work as scripts. No separate compilation step needed.

Multi-file source launcher

Java 8

$ javac *.java
$ java Main
// Must compile all files first
// Need a build tool for dependencies

Java 22+

$ java Main.java
// Automatically finds and compiles
// other source files referenced
// by Main.java

Hover to see modern ➜

JDK 22+ →

Tooling Advanced

Compact object headers

Java 8

// Default: 128-bit object header
// = 16 bytes overhead per object
// A boolean field object = 32 bytes!
// Mark word (64) + Klass pointer (64)

Java 25

// -XX:+UseCompactObjectHeaders
// 64-bit object header
// = 8 bytes overhead per object
// 50% less header memory
// More objects fit in cache

Hover to see modern ➜

JDK 25+ →

Tooling Intermediate

JFR for profiling

Java 8

// Install VisualVM / YourKit / JProfiler
// Attach to running process
// Configure sampling
// Export and analyze
// External tool required

Java 9+

// Start with profiling enabled
$ java -XX:StartFlightRecording=
    filename=rec.jfr MyApp

// Or attach to running app:
$ jcmd <pid> JFR.start

Hover to see modern ➜

JDK 9+ →