specification for null handling in String, StringBuilder, etc. (original) (raw)

Jim Gish jim.gish at oracle.com
Mon Jun 11 21:59:03 UTC 2012

While triaging outstanding String bugs, I was looking at 4247235, "(spec str) StringBuffer.insert(int, char[]) specification is inconsistent"

Although the description is out of date w.r.t. the current code, I did find what I would consider weaknesses (maybe even holes) in the specs relative to this issue.

It appears that the common practice is to spec checked exceptions but not unchecked exceptions (which I understand). For example, in the case mentioned the spec indicates that StringIndexOutOfBoundsException is thrown if the offset is invalid, and is silent about the consequences of the char[] being null. In the latter case, it throws NullPointerException, but the str == null is not checked, rather it simply tries to access str.length and fails if str is null.

My personal feeling is that pre-conditions should be explicitly checked for and be spec'd.

One might argue that the spec is complete, because it says that "The overall effect is exactly as if the second argument were converted to a string by String.valueOf( char[] ),..." If you look at the class javadoc for String there is a statement that "Unless otherwise noted, passing a null argument to a constructor or method in this class will cause a || <http://docs.oracle.com/javase/7/docs/api/java/lang/NullPointerException.html>|NullPointerException| to be thrown." However, if the user simply looks at the javadoc for String.valueOf( char[] ) nothing is said about null handling there. The user would have to have read the class javadoc to catch the reference to NullPointerException. Seems like an unreasonably indirect chain to have to follow, when all we'd have to say is that the original insert method throws NPE if the char[] is null.

I suggest we improve the readability here (and in related places) and tell the user straight off the effect of passing null.

Cheers Jim Gish

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