Garbage friendly alternative to substring()

Question

I have a pipe delimited file which I parse to get system options. The environment is sensitive to heap allocation and we are trying to avoid garbage collection. Below is the code I am using to parse the pipe delimited string. This function is called about 35000 times. I was wondering if there was a better approach that doesn't create as much memory churn. ``` static int countFields(String s) { int n = 1; for (int i = 0; i < s.length(); i++) if (s.charAt(i) == '|') n++; return n; } static String[] splitFields(String s) { String[] l = new String[countFields(s)]; for (int pos = 0, i = 0; i < l.length; i++) { int end = s.indexOf('|', pos); if (end == -1) end = s.length(); l[i] = s.substring(pos, end); pos = end + 1; } return l; } ``` EDIT 1, about java version: For business reasons we are stuck at JDK 1.6.0_25. EDIT 2 about String and String[] usage: The String[] is used to perform the system setup logic. Basically, if String[0].equals("true") then enable debugging. That's the usage patte…

Accepted Answer

Basically, `if String[0].equals("true")` then enable debugging.

You can get rid of the creation of the array and substrings by comparing directly to the input string. That's not avoiding to create the input string like Peter Lawrey's solution does but could be less work to change (although I doubt that).

```
public static boolean fieldMatches(String line, int fieldIndex, String other) {
    int currentField = 0;
    int startIndex = 0;
    while (currentField < fieldIndex) {
        startIndex = line.indexOf('|', startIndex);

// not enough fields
        if (startIndex < 0)
            return false;

startIndex++;
        currentField++;
    }

int start = startIndex;
    int end = line.indexOf('|', startIndex);
    if (end == -1) {
        end = line.length();
    }
    int fieldLength = end - start;

// make sure both strings have the same length
    if (fieldLength != other.length())
        return false;

// regionMatches does not allocate objects
    return line.regionMatches(start, other, 0, fieldLength);
}

public static void main(String[] args) {
    String line = "Config|true"; // from BufferedReader
    System.out.println(fieldMatches(line, 0, "Config"));
    System.out.println(fieldMatches(line, 1, "true"));
    System.out.println(fieldMatches(line, 1, "foobar"));
    System.out.println(fieldMatches(line, 2, "thereisnofield"));
}
```

Output

```
true
true
false
false
```

Garbage friendly alternative to substring()

Solution

Problem

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