General Java Questions III

_istream = new BufferedReader( new

InputStreamReader(fileURL.openStream()) );

j o h n e w e b e r

Or, simpler

getClass().getResourcesAsStream("file.txt"), but you must be sure that

file is in the same directory ( package ) as your class, otherwise you

need play with getClassLoader().getResourceAsStream( "/file.txt" );

Oleg

Q: Difference between loading and instantiating a class???

Well, the subject says it all. What is the difference between loading and instantiating

a class in a JVM.

Second question: What would happen if at runtime I update a class file? Will the JVM

know to use that instead?

Answer: The difference is that when a class is loaded by a ClassLoader it is read in

as a stream of bytes, presumably from a file, but it could just as easily be from over

the network, and then processed or "cooked" into a representation that the VM can

use to make instances of Objects of that classes type. This last part is the

instantiation. You can load a class at runtime with:

Class.forName( "MyClass" );

and instantiate one with:

MyClass mc = Class.forName( "MyClass" ).newInstance();

Cool, ehh. You don t have to know the name of a class at compile time.

>Second question: What would happen if at runtime I update a class file?

>Will the JVM know to use that instead?

Loaded classes are cached because it s quite costly to do the "cooking" I mentioned

above. So it will not be loaded. You may create a separate ClassLoader with new

SecureClassLoader but that will cause all classes _it_ loads to be loaded from this

new ClassLoader but that s not what

you want.

I don t know if you can specify that a class should be loaded from disk again using

the normal ClassLoader. You could very easily make your own ClassLoader in which

case you would have explicit control over such things. Look at java.lang.ClassLoader

and java.lang.Class.

Michael B. Allen

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