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static Number parse(String s) { if (s == null || s.trim().length() == 0) { return 0; } return Long.parseLong(s); }

This piece of code intermittently throws java.lang.NumberFormatException: For input string: "".

Running on Java version 11.0.20+8-LTS-sapmachine.

How is empty string passed into parseLong? I understand s.trim() and s are different instances but doesn't s.trim().length() != 0 infer s is non-empty?

UPDATE: Apologies, I had left out the fact that I am parsing with a DecimalFormat instance (naively thought it did not matter).

static java.text.DecimalFormat df = new java.text.DecimalFormat("#"); static Number parse(String s) throws java.text.ParseException { if (s == null || s.trim().length() == 0) { return 0; } return df.parse(s); }

This code throws java.lang.NumberFormatException: For input string: "" from time to time on a live server. Stack trace:

java.lang.NumberFormatException: For input string: "" at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65) at java.lang.Long.parseLong(Long.java:702) at java.lang.Long.parseLong(Long.java:817) at java.text.DigitList.getLong(DigitList.java:195) at java.text.DecimalFormat.parse(DecimalFormat.java:2121) at java.text.NumberFormat.parse(NumberFormat.java:429)
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    What is the value of s when this error is thrown? Commented Sep 15, 2023 at 14:57
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    Can't reproduce with the empty string (""); if I pass the empty string to parse, I correctly get 0. Just because a string renders like the empty string does not mean that it is the empty string; it may contain invisible zero-width Unicode characters (such as a zero-width space), which trim doesn't trim. Commented Sep 15, 2023 at 15:03
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    Welcome. Best for getting useful advice is follow the Help guidance to provide a minimum executable example of the problem. nb: one method to debug this is to trap NumberException in a debugger so you can inspect the value of s that caused it. It's fairly likely that what you think is happening is not really. Commented Sep 15, 2023 at 16:27
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    I don't see how this would happen considering you test s.trim().length(). Are you sure the NumberFormatException stems from this code? Commented Sep 15, 2023 at 16:33
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    String.valueOf(BigDecimal) cannot return null and cannot return a blank String. You shouldn’t even need to test for those values. Try adding System.out.println(s.length()); right before you call Long.parseLong. That will tell us whether your string is really empty. Commented Sep 15, 2023 at 16:44

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public static Number parse(String s) throws NumberFormatException { if (s == null || s.isBlank()) { return 0; } return Long.parseLong(s); }
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Looking into DigitList class, s definitely is not the input string here. The DigitList's use of StringBuffer tempBuffer is not thread-safe.

private StringBuffer getStringBuffer() { if (tempBuffer == null) { tempBuffer = new StringBuffer(MAX_COUNT); } else { tempBuffer.setLength(0); } return tempBuffer; }

tempBuffer.setLength(0) is what is causing the empty input string. DecimalFormat.digitList and DigitList.tempBuffer are both class members and I am using a singleton DecimalFormat instance creating a race condition.

I am able to reproduce the problem with this line of code

IntStream .range(1, Runtime.getRuntime().availableProcessors() * 3) .parallel() .forEach(s -> parse("123"));

Without the parallel() mode, the issue does not occur.

Having found the root of the issue, I also found this question is essentially a duplicate of https://stackoverflow.com/a/4021932/22569932 where good explanation and solution are provided.

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