.JAVA

Introduction

A .java file holds source code in Java, the language behind the Java platform, whose reference implementation is OpenJDK. The javac compiler turns each class in it into a .class file of bytecode for the Java Virtual Machine. Since Java 11 a single-file program can also be run directly with java Hello.java.

Programs and libraries are usually shipped as .jar archives of the compiled classes rather than as source.

Structure

A Java source file is plain text; since Java 18 the compiler reads it as UTF-8 by default. It starts with an optional package declaration, then import declarations, then one or more classes, interfaces, enums or records. Only one of them may be public, and the file must be named after it: public class Hello lives in Hello.java. The folders normally follow the package name, so com.example.Hello is in com/example/Hello.java.

package com.example;

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

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