Look at ManagedString equality methods

[EvanKirshenbaum]

[imported from HPE issue 332]

A question came up at today's meeting about using ManagedString.equals() to compare against a Java String.

Looking at the code, while ManagedString extends CharSequence, its equals() method only returns true if the object being compared against is another ManagedString.

Although ManagedString specifically extends Comparable<ManagedString>, it does have a compareTo() method that takes a CharSequence, so you can say

if (ms.compareTo(s) == 0) { ... }

This is equivalent to

if (ms.compareTo(ManagedString.valueOf(s)) == 0) { ... }

which will walk the string once (to compute a hash), create a ManagedString equivalent if one doesn’t exist, and then compare them first for equality and then character by character (on the C++ side of the JNI barrier).

The fastest way to determine equality between a ManagedString and a String is probably to use

if (ms == ManagedString.valueOf(s)) {...}

counting on the fact that ManagedStrings are reused for the same content. (Or use equals().)
But this requires walking the string once to compute the hash and looking it up in a table, so if the same string is being compared a lot, it will be far more efficient to keep a ManagedString copy of it.

But I can certainly see cases in which, especially with large strings, it's not worth it to create the ManagedString because we'll be able to get the answer (false or, with compareTo(), not equal to zero) without walking the whole string. String has a contentEquals() method that does this sort of thing, so that would probably be the best name. This could, when the argument isn't a ManagedString, do a character comparison, without interning, stopping at the first mismatch. We could also either implement compareTo(CharSequence) this way or have a second method that does this.