General Java Questions II

Narrowing conversions almost always require an explicit cast.

char to double is one of the widening primitive conversions, so the compiler

automatically treated it as though you had written "if ( r >(double)s)"

by Patricia Shanahan

Answer2: Yes, char is indeed a 16 bit value. However, the actual answer is in the

Java

Language Specification, section 5.6.2, which is at the following URL:

http://java.sun.com/docs/books/jls/second_edition/html/conversions.doc.html#170983

In summary, the char is automagically promoted to a double. No explicit cast is

necessary since the language rules say that it gets "promoted" to a double

by John O Conner

 Is there any performance or other benefit from importing only the classes you

need in a file using something like...

Is there any performance or other benefit from importing only the classes you need in

a file using something like:

import java.util.HashMap;

instead of using ,

import java.util.*;

to import all the classes in a package.

Answer: Strictly speaking, "import java.util.*;" does not import the whole of java.util. It

is an "import on demand" which imports any class or interface in java.util that is

needed. If the first import statement would have done the job, then HashMap is the

only class the second one would import.

No measurable differences in compile time performance. You can do the test, but I

suspect you would get identical byte code, so no difference in run time performance.

There is a practical difference when two packages contain classes with the same

name. Suppose you also imported java.awt.* and tried to declare a List. It would be

ambiguous. If you use the second form you would either import java.util.List or

java.awt.List.

There is also a documentation difference. The first one makes it clear exactly what

imported classes are being used. 

by Patricia Shanahan

Q: == and equals ()... These two still make me confuse a lot of time.

Can somebody give me some thumb rule or explain it to me?

Answer: When you use == with a primitive  int, double, char, ... you are checking that

the values are identical. But if you use == with an object, you are checking that the 2

objects are stored at the same address. In other words the references pointing to the

same object...

Method equals () is different.

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