Question

嗨大家好我是初学者在java :)所以我正在做的是我试图用java建立一个词法分析器，但我试图读取字符串中的下一个字符我试图使用查找功能来检查但我不知道如何在主要使用它。这是代码

 import java.util.*;
 import java.util.Scanner;

 public class LAnalyze{

public static int i;

public static void main(String[] args) {

    String s = "(3+4)*5";
    System.out.println("s = " + s);

    char[] chars = s.toCharArray();

    for (char i = 0; i < 8; i++) {
        if (i == 0) {
            i = s.charAt(0);
            lookup();

        }
    }
}

public int lookup() {

    switch (i) {
    case '(':
        System.out.println("Next Token = " + "'" + i + "'"
                + " Next lexeme = 25");
        break;
    case ')':
        System.out.println("Next Token = " + "'" + i + "'"
                + " Next lexeme = 26");
        break;
    case '+':
        System.out.println("Next Token = " + "'" + i + "'"
                + " Next lexeme = 21");
        break;
    case '-':
        System.out.println("Next Token = " + "'" + i + "'"
                + " Next lexeme = 22");
        break;
    case '*':
        System.out.println("Next Token = " + "'" + i + "'"
                + " Next lexeme = 23");
        break;
    case '/':
        System.out.println("Next Token = " + "'" + i + "'"
                + " Next lexeme = 24");
    default:
        System.out.println("Next Token = " + "'" + i + "'"
                + " Next lexeme = 20");
    }
    return 0;
}
 }



   /* the output is suppose to be something like this:

    Next Token = "(" Next lexeme = 25
    Next Token = "3" Next lexeme = 20
    Next Token = "+" Next lexeme = 21
    .
    .
    .
    Next Token = ")" Next lexeme = 26
     */

Answer 1

您可以通过以下代码来完成。

public static void main(String[] args) {

        String s = "(3+4)*5";
        System.out.println("s = " + s);

        char[] chars = s.toCharArray();

        for (int i = 0; i < chars.length ; i++) {
            //System.out.println("s = " + s);
            lookup(chars[i]);
        }
    }

    public static int lookup(int i) {

        switch (i) {
        case '(':
            System.out.println("Next Token = " + "'" + (char)i + "'"
                    + " Next lexeme = 25");
            break;
        case ')':
            System.out.println("Next Token = " + "'" + (char)i + "'"
                    + " Next lexeme = 26");
            break;
        case '+':
            System.out.println("Next Token = " + "'" + (char)i + "'"
                    + " Next lexeme = 21");
            break;
        case '-':
            System.out.println("Next Token = " + "'" + (char)i + "'"
                    + " Next lexeme = 22");
            break;
        case '*':
            System.out.println("Next Token = " + "'" + (char)i + "'"
                    + " Next lexeme = 23");
            break;
        case '/':
            System.out.println("Next Token = " + "'" + (char)i + "'"
                    + " Next lexeme = 24");
        default:
            System.out.println("Next Token = " + "'" + (char)i + "'"
                    + " Next lexeme = 20");
        }
        return 0;
    }

<强>输出

s = (3+4)*5
Next Token = '(' Next lexeme = 25
Next Token = '3' Next lexeme = 20
Next Token = '+' Next lexeme = 21
Next Token = '4' Next lexeme = 20
Next Token = ')' Next lexeme = 26
Next Token = '*' Next lexeme = 23
Next Token = '5' Next lexeme = 20

希望这会对你有所帮助。

Answer 2

我猜你需要改变循环以实际推进数组的单元格（目前你经常偷看第0个索引处的第一个元素）：

public static void main(String[] args) {

    String s = "(3+4)*5";
    System.out.println("s = " + s);

    for (int i = 0; i < s.length(); i++) {
        char ch = s.charAt(i);
        lookup(ch);
    }
}

public static void lookup(char ch) {

    switch (ch) {
        case '(':
            // ...
    }
}

词法分析器

2 个答案: