General Java Questions II

Answer: See JavaHelp at 

http://www.javasoft.com/products/javahelp/

 you create HTML pages for the main text, and add some XML files for a hierarchical

table of contents and a map from TOC tags to relative URLs giving document

locations.

What is a Just In Time(JIT) compiler?

Answer: It is a JVM that compiles Java instructions (called bytecode) into native

machine instructions at run time and then uses this compiled native code when the

corresponding Java code is needed. This eliminates the constant overhead of

interpretation which tradition first generation JVM s used.

Dave Lee

Is there a collection object like the hashmap or hashtable that stores values in an

ordered path? Vector does this but i need the key/value functionality. hashmaps do

not guarantee the order of the objects.

Answer: Take a look at java.util.TreeMap.

Red Black tree based implementation of the SortedMap interface. This class

guarantees that the map will be in ascending key order, sorted according to the

natural order for the key s class (see Comparable), or by the comparator provided at

creation time, depending on which constructor is used.

Note that this implementation is not synchronized. If multiple threads access a map

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.

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