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vj# : Testing for equality of strings in VJ#
didn't String s; // a global ..... if (s == "") { // blah blah blah } // the above works just fine public void ... String s; // local if (s == "") { // blah blah blah } // blah blah blah never happends even when quick watch shows the expression is true. I finally resorted to s.get_Length == 0 as the expression and it works fine. What gives???? Side bar to MS lurkers. I'm appalled at the quality of the VS 2003 internal doco for J#. Look up boolean expression in the index and all you get is Crystal Repots. UGH!!!!! BTW one of my mottos is that "If Bill Gates had a hand in it, you shouldn't need a manual." (The other is "Bill Gates won.") -- Regards, Al Christoph Senior Consultant and Proprietor Three Bears Software, LLC
Use the CompareTo method on strings. Strings in J# are treated as true
objects, so the equality operator will compile, but provide reference equality, not value equality. -- David Anton www.tangiblesoftwaresolutions.com Instant C#: VB.NET to C# Converter Instant VB: C# to VB.NET Converter Instant J#: VB.NET to J# Converter Clear VB: Cleans up outdated VB.NET code [quoted text, click to view] "Al Christoph" wrote:
> I am really puzzled in one piece of code the obvious worked and in another it > didn't > > String s; // a global > .... > if (s == "") { > // blah blah blah > } > // the above works just fine > public void ... > String s; // local > if (s == "") { > // blah blah blah > } > // blah blah blah never happends even when quick watch shows the expression > is true. > > I finally resorted to s.get_Length == 0 as the expression and it works fine. > > What gives???? > > Side bar to MS lurkers. I'm appalled at the quality of the VS 2003 internal > doco for J#. Look up boolean expression in the index and all you get is > Crystal Repots. UGH!!!!! BTW one of my mottos is that "If Bill Gates had a > hand in it, you shouldn't need a manual." (The other is "Bill Gates won.") > -- > Regards, > Al Christoph > Senior Consultant and Proprietor > Three Bears Software, LLC
Remember: J# is some variant of Java. And Java specs say that == test the
references, not the values. You can fix this by using equals: if (s.equals("")) { ... } Note: as J# gives you access to both the Java framework (JDK) and the .NET framework, you have the choice between: s.equals("") // JDK equals s.Equals("") // .NET equals These 2 methods are equivalent but this is not the case of all string methods. So be careful. For example: s1.compareTo(s2) // JDK version: compares the unicode values (binary comparison) s1.CompareTo(s2) // .NET version: compares according to current locale's collation rules and also s1.indexOf(start, end) // JDK version: 2nd arg is end index s1.IndexOf(start, len) // .NET version: 2nd arg is len of substring So, I suggest that you learn some basics about the JDK and Java (like the fact that == compares references) so that you don't get too many bad surprises. Bruno. "Al Christoph" <AlChristoph@discussions.microsoft.com> a écrit dans le message de news: C7623100-70FC-461F-8F3C-D0831D0545C2@microsoft.com... [quoted text, click to view] >I am really puzzled in one piece of code the obvious worked and in another >it > didn't > > String s; // a global > .... > if (s == "") { > // blah blah blah > } > // the above works just fine > public void ... > String s; // local > if (s == "") { > // blah blah blah > } > // blah blah blah never happends even when quick watch shows the > expression > is true. > > I finally resorted to s.get_Length == 0 as the expression and it works > fine. > > What gives???? > > Side bar to MS lurkers. I'm appalled at the quality of the VS 2003 > internal > doco for J#. Look up boolean expression in the index and all you get is > Crystal Repots. UGH!!!!! BTW one of my mottos is that "If Bill Gates had a > hand in it, you shouldn't need a manual." (The other is "Bill Gates won.") > -- > Regards, > Al Christoph > Senior Consultant and Proprietor > Three Bears Software, LLC > just right software @ just right prices @3bears.biz
In the Java spec it's similar, never use == to compare strings, the
underlying objects will be compared for being the same object. Sun Java VM happens to reuse string data (since strings are "immutable" [you can't edit an existing string, but only make a new string or char array out of it]), so that if you have two string fields holding the same text, chances are they point to the same underlying "string" object. So sometimes "==" will work in Sun Java VM, sometimes not (which can be quite tricky to debug, but still saves some memory space esp. if you have quite big strings) J# could do similarly, but still it doesn't solve your case, use ".equals" method of a string class instance instead for comparison of two Java strings (also the String class maybe has some static method to compare two given strings) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ George Birbilis <birbilis@kagi.com> Microsoft Most Valuable Professional MVP J# for 2004, 2005 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + QuickTime (Delphi & ActiveX: VB, PowerPoint, .NET) + Plugs (InterProcess/Internet communication) http://www.kagi.com/birbilis + Robotics http://www.mech.upatras.gr/~robgroup ......................................................................... [quoted text, click to view] > Use the CompareTo method on strings. Strings in J# are treated as true > objects, so the equality operator will compile, but provide reference > equality, not value equality. > -- > David Anton > www.tangiblesoftwaresolutions.com > Instant C#: VB.NET to C# Converter > Instant VB: C# to VB.NET Converter > Instant J#: VB.NET to J# Converter > Clear VB: Cleans up outdated VB.NET code > > > "Al Christoph" wrote: > > > I am really puzzled in one piece of code the obvious worked and in another it > > didn't > > > > String s; // a global > > .... > > if (s == "") { > > // blah blah blah > > } > > // the above works just fine > > public void ... > > String s; // local > > if (s == "") { > > // blah blah blah > > } > > // blah blah blah never happends even when quick watch shows the expression > > is true. > > > > I finally resorted to s.get_Length == 0 as the expression and it works fine. > > > > What gives???? > > > > Side bar to MS lurkers. I'm appalled at the quality of the VS 2003 internal > > doco for J#. Look up boolean expression in the index and all you get is > > Crystal Repots. UGH!!!!! BTW one of my mottos is that "If Bill Gates had a > > hand in it, you shouldn't need a manual." (The other is "Bill Gates won.") > > -- > > Regards, > > Al Christoph > > Senior Consultant and Proprietor > > Three Bears Software, LLC > > just right software @ just right prices @3bears.biz
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