英文:
ANTLR4 for Java. How to display errors in lexical analysis
问题
如何在词法分析期间显示错误列表（如果有错误）。
我尝试了以下方法，但是我的输出是 [org.antlr.v4.runtime.ConsoleErrorListener@1026c84c]。
我编写的代码：
private static String errorsOutput(String code) {
Java8Lexer lexer = new Java8Lexer(new ANTLRInputStream(code));
CommonTokenStream tokens = new CommonTokenStream(lexer);
Java8Parser parser = new Java8Parser(tokens);
return "" + lexer.getErrorListeners();
}
主类：
String code = "public class Main {public static void main(String[] args) {System.out.println(\"Hello, world\")}}";
System.out.println(errorsOutput(code));
在这个例子中没有显示出错的标志 [;]，我需要程序显示这个错误。
英文:
How can you display a list of errors (if any) during lexical analysis.
I tried the following method, but my output is [org.antlr.v4.runtime.ConsoleErrorListener@1026c84c].
The code I wrote:
private static String errorsOutput(String code) {
Java8Lexer lexer = new Java8Lexer(new ANTLRInputStream(code));
CommonTokenStream tokens = new CommonTokenStream(lexer);
Java8Parser parser = new Java8Parser(tokens);
return ""+lexer.getErrorListeners();
}
Main class:
String code = "public class Main {public static void main(String[] args) {System.out.println("Hello, world")}}";
System.out.println( errorsOutput(code) );
There is no sign in this example
[;] and I need the program to display this error
答案1
得分: 1
你所描述的并不是词法分析，而是语法分析。
以下是如何添加自定义错误监听器并收集消息的方法：
String source = "public class Main {\n" +
" public static void main(String[] args) {\n" +
" System.out.println(\"Hello, world\")\n" +
" }\n" +
"}";
Java8Lexer lexer = new Java8Lexer(CharStreams.fromString(source));
Java8Parser parser = new Java8Parser(new CommonTokenStream(lexer));
parser.removeErrorListeners();
final List<String> errorMessages = new ArrayList<>();
parser.addErrorListener(new BaseErrorListener(){
@Override
public void syntaxError(Recognizer<?, ?> recognizer, Object offendingSymbol, int line, int charPositionInLine, String msg, RecognitionException e) {
errorMessages.add(msg);
}
});
parser.compilationUnit();
System.out.println("errorMessages: " + errorMessages);
请注意，上面的代码段会显示消息 mismatched input '(' expecting '.'，因为在这个位置：
System.out.println(
// ^
// |
// '-- 这里
它无法匹配 println 语句，因为缺少了 ;，所以它会尝试匹配另一个 . 来完成一个 methodInvocation，但也会失败。这只是语法的结构，除了重写大部分语法，没有太多可以做的。
如果你解析这段代码：
String source = "public class Main {\n" +
" public static void main(String[] args) {\n" +
" foo()\n" +
" }\n" +
"}";
那么你会得到消息：missing ';' at '}'。
英文:
What you're describing is not lexical analysis, but syntactic analysis.
This is how you add a custom error listener and collect messages:
String source = "public class Main {\n" +
" public static void main(String[] args) {\n" +
" System.out.println(\"Hello, world\")\n" +
" }\n" +
"}";
Java8Lexer lexer = new Java8Lexer(CharStreams.fromString(source));
Java8Parser parser = new Java8Parser(new CommonTokenStream(lexer));
parser.removeErrorListeners();
final List<String> errorMessages = new ArrayList<>();
parser.addErrorListener(new BaseErrorListener(){
@Override
public void syntaxError(Recognizer<?, ?> recognizer, Object offendingSymbol, int line, int charPositionInLine, String msg, RecognitionException e) {
errorMessages.add(msg);
}
});
parser.compilationUnit();
System.out.println("errorMessages: " + errorMessages);
Note that the snippet above will display the message mismatched input '(' expecting '.' because at this location:
System.out.println(
// ^
// |
// '-- here
it cannot match a println statement because of the missing ; so it then tries to match another . to complete a methodInvocation, which also fails. That is just how the grammar is structured, not much to do about that (besides rewriting large parts of it).
If you parse this:
String source = "public class Main {\n" +
" public static void main(String[] args) {\n" +
" foo()\n" +
" }\n" +
"}";
then you do get the message: missing ';' at '}'
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