替换字符串中的字符

Question

So I'm trying to iterate over a string and replace ever occurrence of a given substring with a new value. I can't seem to figure out what the problem with my code is because it doesn't seem to make any changes to the strings i run through it.

i create a new string nS that starts out as just “”, and am iterating through the template viewing each character as a substring s. In in every case that something needs to be replaced with a value i append said value on to the nS, else it just appends the current substring as is.

@Override
public String format(String template) {
    String nS = "";
    for (int i = 0, n = template.length(); i < n; i++) {
        String s = template.substring(i, i + 1);
        switch (s) {
            case "%%":
                nS = nS.concat("%");
                break;

            case "%t":
                nS = nS.concat(String.valueOf(inSeconds()));
                break;
       }
    }
    return nS;
}

the actual code has many more cases but i left them out so that its not as overwhelming.

Answer 1

The ending index in the 2-arg substring method is exclusive .

The substring begins at the specified beginIndex and extends to the character at index endIndex - 1.

beginIndex - the beginning index, inclusive.

endIndex - the ending index, exclusive.

You are getting a substring of exactly one character, not 2. Try i + 2 , after the appropriate bounds-checking:

String s = template.substring(i, i + 2);

Answer 2

Assuming performance is not a big issue I would do

public String format(String template) {
    return template.replaceAll ("%%", "\uffff")
                .replaceAll("%t", ""+inSeconds())
                .replaceAll("\uffff", "%");
}

Answer 3

What you're describing attempting to do sounds like you're trying to rewrite String.replace()

Given String s = "My Name Is Bob"

and you would like to replace "Bob" with "Susan" all you need to do is:

String s = "My Name is Bob";
String n = s.replace("Bob", "Susan");
System.out.println(n); //My Name is Susan
System.out.println(s); //My Name is Bob

Another option, is to break the string into a character array and iterate over it.

String s = "My Name is Bob";
char[] bits = s.toCharArray();
for(char c : bits) {
   // logic
}

Compare two characters at once:

String s = "My Name is Bob";
char[] bits = s.toCharArray();
for(int i = 0; i < bits.length; i++) {
    if(i + 1 <= bits.length) {
       String searchFor = "" + bits[i] + bits[i + 1];
       // logic
    }
}