Java 将表达式解析为AST

参考：https://blog.51cto.com/u_16175468/8063959

https://blog.51cto.com/u_16213690/7305835

import org.antlr.v4.runtime.*;
import org.antlr.v4.runtime.tree.*;
 
public class ExpressionParser {
    public static void main(String[] args) throws Exception {
        // 创建输入流
        InputStream input = new FileInputStream("expression.txt");
        
        // 创建字符流
        ANTLRInputStream stream = new ANTLRInputStream(input);
        
        // 创建词法分析器
        MyLexer lexer = new MyLexer(stream);
        
        // 创建Token流
        CommonTokenStream tokens = new CommonTokenStream(lexer);
        
        // 创建解析器
        MyParser parser = new MyParser(tokens);
        
        // 开始解析
        ParseTree tree = parser.start();
        
        // 打印AST
        System.out.println(tree.toStringTree());
    }
}

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