Compact source files

Write a complete program without class declaration or public static void main.

Tooling

Code Comparison

✕ Java 8

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println(
            "Hello, World!");
    }
}

✓ Java 25

void main() {
    IO.println("Hello, World!");
}

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Why the modern way wins

🚀

Zero ceremony

No class, no public static void main, no String[] args.

🎓

Beginner-friendly

New programmers can write useful code from line 1.

📝

Script-like

Perfect for quick prototypes, scripts, and examples.

Old Approach

Main Class Ceremony

Modern Approach

void main()

Since JDK

Difficulty

Beginner

JDK Support

Compact source files

Available

Finalized in JDK 25 LTS (JEP 512, Sept 2025).

How it works

Compact source files remove the ceremony of class declarations and the main method signature for simple programs. Combined with implicit import of java.io.IO, even println is available directly.

Type inference with var

Java 8

Map<String, List<Integer>> map =
    new HashMap<String, List<Integer>>();
for (Map.Entry<String, List<Integer>> e
    : map.entrySet()) {
    // verbose type noise
}

Java 10+

var map = new HashMap<String, List<Integer>>();
for (var entry : map.entrySet()) {
    // clean and readable
}

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JDK 10+ →

Language Beginner

Text blocks for multiline strings

Java 8

String json = "{\n" +
    "  \"name\": \"Duke\",\n" +
    "  \"age\": 30\n" +
    "}";

Java 15+

String json = """
    {
      "name": "Duke",
      "age": 30
    }""";

Hover to see modern ➜

JDK 15+ →

Language Beginner

Switch expressions

Java 8

String msg;
switch (day) {
    case MONDAY:
        msg = "Start";
        break;
    case FRIDAY:
        msg = "End";
        break;
    default:
        msg = "Mid";
}

Java 14+

String msg = switch (day) {
    case MONDAY  -> "Start";
    case FRIDAY  -> "End";
    default      -> "Mid";
};

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JDK 14+ →