I am trying to validate the input string: (10 30i) or should I say (10 30i)\n by using a parser, but am unable to implement StreamTokenizer.TT_EOL so that my program is done when it sees ); checks if it maches ')' (it does) and sees that next token is end of line EOL ( or should it be EOF?) ; and prints out "Reached the end!". Here is my code, I have tried to implement EOL but was unsuccesful:

import java.io.*;
import static java.util.Objects.requireNonNull;

public class Test2 {

    private int lookahead;
    private StreamTokenizer tokenizer;
    private final Reader input;
    private final Writer output;

    public Test2(Reader input, Writer output) throws IOException {
        this.input = requireNonNull(input);
        this.output = requireNonNull(output);
        this.lookahead = this.input.read();
    }

    private void next() throws IOException {

        lookahead = tokenizer.nextToken();

        if (lookahead == StreamTokenizer.TT_EOL) {
            System.out.println("Reached the end!");
        }

        if (tokenizer.sval != null) {
            char ch = tokenizer.sval.charAt(0);
            lookahead = (int) ch;
        }
    }

    private void match(int expected) throws IOException {

        if (lookahead != expected ) {

            switch (expected) {

                case '(':
                    System.out.println("Error, missing opening round bracket.");
                    break;

                case ')':
                    System.out.println("Error, missing closing round bracket.");
                    break;

                case 'i':
                    System.out.println("Error, missing i.");
                    break;

                case ' ':
                    System.out.println("Error, missing  ");
            }
        }  else {
            next();
        }
    }

    private void parseExpr() throws IOException {

        if (lookahead == '(') {

            match('(');

            if (lookahead == StreamTokenizer.TT_NUMBER) {
                next();
            } else {
        System.out.println("Error, missing number.");
                return;
            }

            match(' ');

            if (lookahead == StreamTokenizer.TT_NUMBER) {
                next();
            } else {
                System.out.println("Error, missing number.");
                return;
            }

            match('i');

            match(')');


            System.out.println("We have a complex number.");

            next();

            parseExpr();

            if (lookahead == ' ') {
                next();
                parseExpr();
            }


        }
    }


    public static void main(String[] args) throws IOException {
        InputStreamReader reader = new InputStreamReader(System.in);
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        OutputStreamWriter writer = new OutputStreamWriter(outputStream);

        Test2 parse = new Test2(reader, writer);

        parse.tokenizer = new StreamTokenizer(reader);

        parse.parseExpr();

        writer.close(); // Close and flush output stream writer.

        String output = outputStream.toString();
        System.out.println("Output generated by parser: "   output);
    }
}

I tried debugging it , it works fine until ) is recognized as a token.

This is the last step of the debugger, then it stops working:

enter image description here

Please help me :( even ideas on what changes I can make to whole code would help me a lot.

CodePudding user response：

The issue is that the tokenizer will not recognize an EOL by default. You will need to enable this functionality with tokenizer.eolIsSignificant(true);.

After parse.tokenizer = new StreamTokenizer(reader); add this line parse.tokenizer.eolIsSignificant(true); and the tokenizer should recognize EOLs