The abstract syntax tree in the Java class library: use@Babel/Types framework for analysis and operation
The abstract syntax tree (AST) in the Java class library: Use the@Babel/Types framework for analysis and operation
Overview:
Abstract grammar tree (AST) is a widely used data structure in programming language to represent the abstract structure of code.It captures the syntax, semantics, and structure of the code by analyzing the source code into a series of nested nodes.AST played an important role in the fields of static code analysis, code optimization, code conversion, and code generation.This article will introduce how to use the@Babel/Types framework in the Java class library to analyze and operate AST.
@Babel/Types framework:
@Babel/Types is a Java class library used to operate and generate AST nodes.It provides a set of simple and easy -to -use APIs, making parsing, traversal, and modification of AST to simple and efficient.@Babel/Types is part of the Babel compiler. Babel is a famous JavaScript compiler for the latest ECMAScript standard into code that can run in different environments.
Use@Babel/Types Analysis code:
To use@Babel/Types parsing code, we need to convert the source code to AST for first.You can use the@Babel/Parser module to achieve this goal.Here are examples of using@Babel/Types and@Babel/Parser to analyze code:
import org.json.JSONException;
import org.json.JSONObject;
import com.github.javaparser.JavaParser;
import com.github.javaparser.ParseProblemException;
import com.github.javaparser.ast.CompilationUnit;
import com.github.javaparser.printer.JsonPrinter;
import com.github.javaparser.printer.lexicalpreservation.LexicalPreservingPrinter;
public class ASTParser {
public static JSONObject parse(String code) throws JSONException {
try {
CompilationUnit cu = JavaParser.parse(code);
JsonPrinter printer = new JsonPrinter(true);
LexicalPreservingPrinter.setup(cu);
String json = printer.output(cu);
return new JSONObject(json);
} catch (ParseProblemException e) {
e.printStackTrace();
return null;
}
}
public static void main(String[] args) throws JSONException {
String code = "public class MyClass {
" +
" public static void main(String[] args) {
" +
" int x = 10;
" +
" System.out.println(x);
" +
" }
" +
"}";
JSONObject ast = parse(code);
System.out.println(ast);
}
}
In the above example, we used the Javaparser class to create a compilationUnit object from the source code.We then print AST as JSON string with JSONPRINTER, and finally convert it to JSONObject.
Use@babel/types to operate AST:
Once the code is parsed to AST, we can use the API provided by@Babel/Types to operate and modify AST.The following is an example using@Babel/Types framework to modify AST:
import org.json.JSONException;
import org.json.JSONObject;
import com.github.javaparser.JavaParser;
import com.github.javaparser.ast.CompilationUnit;
import com.github.javaparser.ast.body.MethodDeclaration;
import com.github.javaparser.ast.stmt.BlockStmt;
import com.github.javaparser.ast.stmt.Statement;
import com.github.javaparser.printer.JsonPrinter;
import com.github.javaparser.printer.lexicalpreservation.LexicalPreservingPrinter;
public class ASTModifier {
public static void modify(JSONObject jsonAST) throws JSONException {
CompilationUnit cu = JavaParser.parse(jsonAST.toString());
LexicalPreservingPrinter.setup(cu);
// Modify all the methods in AST to a empty block that returns 0
cu.findAll(MethodDeclaration.class).forEach(method -> {
BlockStmt newBlock = new BlockStmt();
newBlock.addStatement(new ReturnStmt(new IntegerLiteralExpr(0)));
method.setBody(newBlock);
});
JsonPrinter printer = new JsonPrinter(true);
String modifiedAST = printer.output(cu);
System.out.println(modifiedAST);
}
public static void main(String[] args) throws JSONException {
String astJson = "{\"type\":\"CompilationUnit\",\"children\":[{\"type\":\"ClassOrInterfaceDeclaration\",\"children\":[{\"type\":\"MethodDeclaration\",\"children\":[{\"type\":\"BlockStmt\",\"children\":[{\"type\":\"Statement\",\"children\":[{\"type\":\"LocalVariableDeclaration\",\"children\":[{\"type\":\"VariableDeclarator\",\"children\":[{\"type\":\"VariableDeclaratorId\",\"children\":[{\"type\":\"IDENTIFIER\",\"value\":\"x\"}]}]},{\"type\":\"IntegerLiteralExpr\",\"value\":\"10\"}]}]},{\"type\":\"Statement\",\"children\":[{\"type\":\"ExpressionStmt\",\"children\":[{\"type\":\"MethodCallExpr\",\"children\":[{\"type\":\"FIELD_ACCESS\",\"children\":[{\"type\":\"ThisExpr\"},{\"type\":\"IDENTIFIER\",\"value\":\"out\"}]},{\"type\":\"IDENTIFIER\",\"value\":\"println\"}],\"name\":{\"type\":\"IDENTIFIER\",\"value\":\"println\"},\"arguments\":[{\"type\":\"IDENTIFIER\",\"value\":\"x\"}]}}]}]},{\"type\":\"IDENTIFIER\",\"value\":\"main\"}]}]}]}";
JSONObject ast = new JSONObject(astJson);
modify(ast);
}
}
In the above examples, we re -built the AST object from the JSON string, and use the Findall method to find all the methods to declare.Then, we created a new empty block and used ReturnSTMT to set it to the new body of the method.Finally, we printed the modified AST as a JSON string.
Summarize:
Abstract grammar tree (AST) is a data structure commonly used in programming languages to represent the abstract structure of code.Using the@Babel/Types framework in the Java class library can easily analyze and operate AST.The example code of this article shows how to use the@Babel/Types framework to analyze and modify AST.By mastering the basic concepts and usage methods of AST, you can play a greater role in the scenes such as static code analysis, code optimization, and code conversion.
