Java：基于定界符解析字符串

Question

I have to design an interface where it fetches data from machine and then plots it. I have already designed the fetch part and it fetches a string of format A&B@.13409$13400$13400$13386$13418$13427$13406$13383$13406$13412$13419$00000$00000$

First five A&B@. characters are the identifier. Please note that the fifth character is new line feed ie ASCII 0xA .

The function I have written -

   public static boolean checkStart(String str,String startStr){

       String Initials = str.substring(0,5);
       System.out.println("Here is start: " + Initials);       
       if (startStr.equals(Initials))
        return true;
        else
        return false;
     }

shows Here is start: A&B@. which is correct.

Question 1: Why do we need to take str.substring(0,5) ie when I use str.substring(0,4) it shows only - Here is start: A&B@ ie missing new line feed . Why is New Line feed making this difference.

Further to extract remaing string I have to use s.substring(5,s.length()) instead of s.substring(6,s.length())

ie s.substring(6,s.length()) produces 3409$13400$13400$13386$13418$13427$13406$13383$13406$13412$13419$00000$00000$ ie missing the first char after the identifier A&B@.

Question 2:

My parsing function is:

public static String[] StringParser(String str,String del){
    String[] sParsed = str.split(del);
     for (int i=0; i<sParsed.length; i++) {
                     System.out.println(sParsed[i]);
              }
    return sParsed;
     }

It parses correctly for String String s = "A&B@.13409/13400/13400/13386/13418/13427/13406/13383/13406/13412/13419/00000/00000/"; and calling the function as String[] tokens = StringParser(rightChannelString,"/");

But for String such as String s = "A&B@.13409$13400$13400$13386$13418$13427$13406$13383$13406$13412$13419$00000$00000$" , the call String[] tokens = StringParser(rightChannelString,"$"); does not parse the string at all.

I am not able to figure out why this behaviour. Can any one please let me know the solution?

Thanks

Answer 1

Regarding question 1, the java API says that the substring method takes 2 parameters:

• beginIndex the begin index, inclusive .
• endIndex the end index, exclusive .

So in your example

String: A&B@.134
Index:  01234567

substring(0,4) = indexes 0 to 3 so A&B@, that's why you have to put 5 as the second parameter to recover your line delimiter.

Regarding question 2, I guess that the split method takes a regexp in parameter and $ is a special character. To match the dollar sign I guess you have to escape it with the \\ character (as \\ is a special char in strings so you must also escape it).

String[] tokens = StringParser(rightChannelString,"\\$");

Answer 2

Q1: review the description of substring in the documentation:

Returns a new string that is a substring of this string.
The substring begins at the specified beginIndex and extends to the
character at index endIndex - 1. Thus the length of the substring
is endIndex-beginIndex. 

Q2: the split method takes a regular expression for the separator. $ is a special character for regular expressions, it matches the end of the line.