2

大家好，我是java的初学者:)所以我正在做的是我试图使用java构建一个词法分析器但我坚持试图读取字符串中的下一个字符我试图使用查找函数来检查但我不知道如何主要使用它。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
     */
4

2 回答 2

2

您可以通过以下代码进行操作。

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;
    }

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

希望这会帮助你。

于 2012-05-08T18:51:26.913 回答
0

我想您需要更改循环以实际推进数组的单元格（目前您不断查看第 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 '(':
            // ...
    }
}
于 2012-05-08T18:53:10.083 回答