如何使用Antlr在Java中获取.txt输入文件的解析树

问题描述

我从学校得到了这个演示代码，应该给我看一棵解析树。在生成解析器并在该类中测试规则之后，我应该运行java类，但是我似乎没有获得解析器树。有人知道我在做什么错吗？

以及Java文件中的代码

MyAntlrDemo

import java.io.IOException;

import org.antlr.v4.runtime.*;
import org.antlr.v4.runtime.tree.ParseTree;

/**
 * Antlr Java Parser Demo: read a Java file and print methods found by visiting the parse tree.
 * Don't forget to generate ANTLR Java parser class files first!
 */
public class MyAntlrDemo extends Java8ParserBaseVisitor<Void> {
    /**
     * Main Method
     */
    public static void main(String[] args) throws IOException {
        //String file = "./src/MyAntlrDemo.java"; // input this source  file
        String file = "./exampleJava.txt";  // a shorter Java example input

        CharStream chars = CharStreams.fromFileName(file);
        Java8Lexer lexer = new Java8Lexer(chars);
        CommonTokenStream tokens = new CommonTokenStream(lexer); // lexer converts text to tokens
        Java8Parser parser = new Java8Parser(tokens);
        ParseTree tree = parser.compilationunit(); // create tree from staring rule: compilationunit
        System.out.println("Number of Syntax errors found: " + parser.getNumberOfSyntaxErrors());
        // walk the tree and do something with it
        MyAntlrDemo visitor = new MyAntlrDemo(); // extends JavaBaseVisitor<Void>
        System.out.println("STARTING VISIT");
        visitor.visit(tree); // calls visitcompilationunit and other overridden methods below
    }

    @Override
    public Void visitcompilationunit(Java8Parser.compilationunitContext ctx) {
        System.out.println("Inside visitcompilationunit");
        return visitChildren(ctx);
    }

    @Override
    public Void visitMethodDeclaration(Java8Parser.MethodDeclarationContext ctx) {
        System.out.println("found method:" + ctx.getText());
        System.out.println("Methodname: " + ctx.methodHeader().methodDeclarator().Identifier().getText());
        return super.visitMethodDeclaration(ctx);
    }

}

也是.txt文件

ExampleJava.txt

class Jan {
  private int foo; // comment
  public Jan() { }
  public int eenMethode(){
    return foo * 2;
  }
}

输出消息：

ANTLR预览：

解决方法

您必须更改上一张图片中的选择，或者将代码粘贴到antlr预览中

检查示例后，请参阅右侧的分析树 您必须右键单击文件=>“ configure antlr” =>设置生成的路径=>设置生成的目录=>保存

右键单击文件=>“生成antlr识别器”

生成的包含分析树的文件将位于您选择的生成目录中