Re: Static methods

From:

"jupiter" <jupiter49byebyeSpam@msn.com>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 26 Dec 2006 23:19:10 -0500

Message-ID:

<TLWdnXMRSpwlaQzYnZ2dnUVZ_t-mnZ2d@comcast.com>

"Stefan Ram" <ram@zedat.fu-berlin.de> wrote in message
news:static-fields-20061226233702@ram.dialup.fu-berlin.de...

"jupiter" <jupiter49byebyeSpam@msn.com> writes:

In my BankAccount class I have a variable declared as private
static
int pin.

What's the matter with that? There's only one customer at his
lousy bank.

/* Why? Here is a class with a static field: */

Sorry, I was only making a joke (about the bank only having one
customer), Stephan.

Nevertheless, you provided a nice example. Thanks, I've never
stepped through it like that.

public class Scan { static int i = 0; public static int get(){
return i++; }}

/* Let's create two instances of it: */

public class Main
{ public static void main( java.lang.String[] args ) throws
java.lang.Exception
{ final java.lang.Class instance1 = new
ScanLoader().loadClass( "Scan" );
   final java.lang.Class instance2 = new
ScanLoader().loadClass( "Scan" );
   final java.lang.Class[] c = new java.lang.Class[]{};
   final java.lang.Object[] o = new java.lang.Object[]{};
   java.lang.System.out.println( instance1.getMethod( "get",
c ).invoke( null, o ));
   java.lang.System.out.println( instance1.getMethod( "get",
c ).invoke( null, o ));
   java.lang.System.out.println( instance2.getMethod( "get",
c ).invoke( null, o ));
   java.lang.System.out.println( instance2.getMethod( "get",
c ).invoke( null, o )); }}

/* There are really two different static fields, as they can
    count independently:

0
1
0
1

    The rest of the code: */

class ScanLoader extends ClassLoader
{ public ScanLoader()
{ super(ScanLoader.class.getClassLoader()); }
public java.lang.Class<?> loadClass( final java.lang.String
className)
throws ClassNotFoundException
{ return findClass( className ); }
public java.lang.Class<?> findClass( final java.lang.String
className )
{ byte classByte[];
   java.lang.Class<?> result = null;
   if( "java.lang.Object".equals( className ))return
java.lang.Object.class;
   try
   { java.lang.String classPath =
     ((java.lang.String)ClassLoader.getSystemResource
     ( className.replace( '.', java.io.File.separatorChar ) +
".class" ).getFile() ).
     substring( 1 );
     classByte = loadClassData(classPath);
     result =
defineClass(className,classByte,0,classByte.length,null);
     return result; }
   catch(final java.lang.Exception e){ throw new
java.lang.RuntimeException(e); }}
private byte[] loadClassData
( final java.lang.String className )
throws java.io.IOException
{ final java.io.File f = new java.io.File( className );
   final int size =( int )f.length();
   final byte buff[] = new byte[ size ];
   { java.io.FileInputStream fis = new java.io.FileInputStream(
f );
     { java.io.DataInputStream dis = new
java.io.DataInputStream( fis );
       dis.readFully( buff );
       dis.close(); }}
   return buff; }}