Denis Jaccard wrote:
>
> Please stop all these mistakes ;-).
I'm really sorry, but it's you who is wrong, Denis. I really hope you haven't
been passing this information to your students.
> In the "heart" of Java, the == operator has been overloaded (since I
> speak French, I'm not sure this is the right term) for a few classes of
> the java.lang package. String, like Integer, Double and other wrapping
> classes, belongs to these classes. Though, the == operator and the
> equals method do the same thing : it compares the content of the String
> instance.
Nope. == always compares object references if applied to a reference type.
The operation of all operators is defined in the JLS. There's no such
overloading.
> Sample :
>
> String str1="Hello";
> String str2="Hello";
Note that there will only be one instance of the String "Hello" in the string
table - Java is smart enough to recycle things if possible.
Try this:
String str3 = new String(str1);
> if(str1==str2) {
> System.out.println("str1==str2");
> }
> if(str1.equals(str2)) {
> System.out.println("str1.equals(str2))");
> }
if(str1==str3)
System.out.println("The same");
else
System.out.println("str3 and str1 are different"); // this will run
> The two "if conditions" are true although the two String objects are
> located into two different memory addresses.
But they're not - that's the flaw in your example.
> I hope this clarifies the way String works. Be careful, it's not the
> same for StringBuffer. For StringBuffer, Bruce, Vance, Craig and others
> are right.
It's exactly the same for StringBuffer...
StringBuffer sb1 = new StringBuffer("Foo");
StringBuffer sb2 = new StringBuffer("Foo");
sb1 will never be the same as sb2.
== on object references ALWAYS compares the references.
Also, see the JLS, section 15.20.3, available at
http://java.sun.com/docs/books/jls/html/15.doc.html#236163 -
it specifically states:
"While == may be used to compare references of type String,
such an equality test determines whether or not the two operands
refer to the same String object."
Ethan
--
Ethan Henry [EMAIL PROTECTED]
Java Evangelist, KL Group http://www.klg.com
"Software Development Productivity"
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