关于.class文件与字节码的关系及编译后字节码位置的技术咨询

Great questions—let’s unpack this in straightforward terms to eliminate any confusion:

1. Are .class files bytecode, or do they contain bytecode? #

The short, precise answer: .class files contain Java bytecode, but they aren’t just bytecode.

Think of a .class file as a structured binary container. Inside it, you’ll find two key components:

• The core Java bytecode: This is the low-level instruction set the JVM (Java Virtual Machine) executes directly.
• Critical metadata: Details like class names, method signatures, constant pools (for shared values like strings), access modifiers, and references to other classes.

Bytecode is the executable heart of the file, but the .class format wraps it alongside the extra data the JVM needs to load, understand, and run the class.

2. After compiling with javac.exe, is the .class file bytecode, and where does the bytecode live? #

Same logic applies here: The generated .class file holds bytecode (it isn’t equivalent to bytecode itself).

As for where the bytecode ends up:

• By default, when you run javac MySourceFile.java in Command Prompt, the resulting MySourceFile.class file (which contains the bytecode) saves in the same directory as your original .java source file.
• To specify a custom output directory, use the -d flag with javac. For example:

  javac -d ./output_classes MySourceFile.java
  

  This will create an output_classes folder (if it doesn’t exist) and store the .class file (with bytecode inside) there.

内容的提问来源于stack exchange，提问作者Jemu Ju