InputStreamReader。read（）不读取/跳过第一个字符？

Question

我试图编写一个简单的复数计算器，可以计算以下表达式：

• 输入1：（10 30i）（90 20i）
• 预期输出：（100 50i）
• 输入2：（10 30i）-（90 20i）
• 预期输出：（-80 10i）

编辑：我注意到第一次前瞻读取是10而不是40（ascii值 '(' ) . 我如何解决这个问题？

我的代码：

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

public class Parser {

    private int lookahead;
    private StreamTokenizer tokenizer;
    private final Reader input;
    private final Writer output;
    
    
    public Parser(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();
    }
    
    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 +");
                    
                default:
                    return;
            }
        } else {
            next();
        }
    }
    
    private void parseExpr() throws IOException {
      
       long[] parameters = new long[4];
       int i = 0;
       
        if (lookahead == '(') {
            match('(');
            
            if (lookahead == StreamTokenizer.TT_NUMBER) {
                parameters[i] = lookahead;
                i++;
                next();
                
            } else {
                System.out.println("Not a number.");
                return;
            }
            
            match('+');
            
            if (lookahead == StreamTokenizer.TT_NUMBER) {
                parameters[i] = lookahead;
                i++;
                next();
            } else {
                System.out.println("Not a number.");
                return;
            }
            
            match('i');
            match(')');
            
            if(lookahead == '+'){
                next();
                parseExpr();
                System.out.println("(" + (parameters[0]+parameters[2]) + "+" +(parameters[1]+parameters[3]) + "i)");
            }
            
            if(lookahead == '-'){
                next();
                parseExpr();
                System.out.println("(" + (parameters[0]-parameters[2]) + "+" +(parameters[1]-parameters[3]) + "i)");
            }
        }
        
        System.out.println("Sorry, I can't help you");
    }
    
    public static void main(String[] args) throws IOException {
        InputStreamReader reader = new InputStreamReader(System.in);
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        OutputStreamWriter writer = new OutputStreamWriter(outputStream);

        Parser parse = new Parser(reader, writer);
        parse.parseExpr();

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

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

但它总是输出“对不起，我帮不了你。”

Answer 1

我已经测试了您的代码，我有两条意见可以帮助您：

1. 您始终会收到相同的错误消息，因为您尚未将“令牌化器”日化，请尝试使用tokenizer=new-StreamTokenizer（reader） 在主方法中

我希望这有帮助，让我知道。