What processes does javac compilation include?

What processes does javac compilation include?

The java compilation process is mainly divided into the following steps:

1. Lexical analysis : Convert the characters in the source code (various keywords, variables, etc.) into a set of tokens, the smallest unit of program writing for a single character, and token is the smallest unit of the compilation process.

2. Syntax analysis: Construct a collection of tokens into an abstract syntax tree. Each node of the syntax tree represents a syntax structure in the code (such as package, type, interface, modifier, etc.).

3. Fill the symbol table: The symbol table is a table composed of a set of symbol addresses and symbol information. The exit from the process of filling the symbol table is a pending list containing the top-level nodes of each abstract syntax tree (and package-info.java).

4. Plug-in annotation processor processes annotations: The annotation processor can add, delete, or modify any element of the abstract syntax tree. Therefore, whenever the annotation processor modifies the syntax tree, steps 1, 2, and 3 will be re-executed until the annotation processor no longer modifies the syntax tree. Each cycle process is called a Round.

5. Semantic analysis: Context-sensitive review of source programs that are correct in syntax tree structure.

• Annotation check: including whether variables are declared, whether variables and assignment types match, etc., and constant folding.

• Data and control flow analysis: further verification of program context logic. Including whether variables are assigned values ​​before use, whether methods have return values, whether exceptions are handled correctly, etc.

6. Decode syntax sugar: Convert advanced syntax (such as generics, variable parameters, unboxing, etc.) into basic syntax structures. These are not supported when the virtual machine is running. Advanced syntax.

7. Generate bytecode: Convert the information in the syntax tree and symbol table into bytecode and write it to the disk, while performing a small amount of code addition and conversion work.

Most of the above content is excerpted from: "In-depth Understanding of Java Virtual Machine" -- Zhou Zhiming

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