When "ab".equals("ab") returns false

Question

One thing that really ticks me off in java is the narrow-mindedness of equals. Given the specifications laid out in Object.equals(), it becomes extremely tricky to ever have equals return true for comparison of Objects of different types.
"So what?" You say. Well, back to the original title of this topic, it is possible for ab to not equal ab in the following cases.
String ab = "ab";
StringBuffer buffer = new StringBuffer(ab);
char[] buf2 = new char[] {'a','b'}
ab.equals(buffer) == always false
buffer.equals(ab) == always false
ab.equals(buf2) == always false
buf2.equals(ab) == always false
I could see how you probably couldn't and shouldn't make a String equal to a character array, but what about a StringBuffer??? I mean, come on! No one's going to try to compare a stringbuffer to a string or vice versa and get frustrated when it doesn't work?
"Well," perhaps you are saying to yourself, "perhaps those that don't understand the way java is implemented could fall into that trap". While you are considering this thought, download the jdk1.5 source code and have a look at java.text.ChoiceFormat, especially applyPattern and how it uses equals

Answer 1

One thing that really ticks me off in java is the
narrow-mindedness of equals. Given the specifications
laid out in Object.equals(), it becomes extremely
tricky to ever have equals return true for comparison
of Objects of different types.
the equals method in the object class does the same thing as == does, meaning only when you are comparing the same object, it returns true. it is meant to be overridden in subclasses for real situations.
"So what?" You say. Well, back to the original title
of this topic, it is possible for ab to not equal ab
in the following cases.
the title is misleading, "ab" will always equals to "ab". the following is a different matter:
String ab = "ab";
StringBuffer buffer = new StringBuffer(ab);
char[] buf2 = new char[] {'a','b'}
ab.equals(buffer) == always falsethe equals implementation will return true only two objects are of string type. stringbuffer is not, so it will always return false.
buffer.equals(ab) == always falsestringbuffer does no have its own implementation of the equals method, it uses the one in the object class, which will return true if you are comparing the same object, only if == is true, equals will be true. here it is apparently not the xase, so it will reuturn false always.
ab.equals(buf2) == always false
buf2.equals(ab) == always false
see above.
I could see how you probably couldn't and shouldn't
make a String equal to a character array, but what
about a StringBuffer??? I mean, come on! No one's
going to try to compare a stringbuffer to a string or
vice versa and get frustrated when it doesn't work?
see above.
considering this thought, download the jdk1.5 source
code and have a look at java.text.ChoiceFormat,
especially applyPattern and how it uses equalsi dont see any difference in 1.5, as comapred to 1.4. you were probabally not so careful, as i saw in the src a line labled as "tempBuffer", but it was actually a string.