General Java Questions I

concurrently, and at least one of the threads modifies the map structurally, it must be

synchronized externally.

Most people asked why there is an error, but my question is why this is NOT an

error

Please take a look:

r is a number and s is a character, why can I put them together to make a comparison

without compilation error? Could somebody tell me... thank you

double r = 34.5;

char s =  c ;

if (r > s) {

   System.out.println("r > s");

} else {

   System.out.println("r < s");

}

Answer1: char is considered to be an arithmetic type, acting as a 16 bit unsigned

integer.

Conversions among the primitive types are divided into three categories:

identity, widening, and narrowing. The identity conversions are the trivial ones like

char to char. The widening conversions all have the effect of preserving the

approximate magnitude of the result, even if it cannot be represented exactly in the

new type. The narrowing conversions are the remaining conversions that may

destroy the magnitude information.

Identity and widening conversions can be inserted automatically by the compiler.

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.*;

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