Re: Static methods

From:

ram@zedat.fu-berlin.de (Stefan Ram)

Newsgroups:

comp.lang.java.programmer

Date:

26 Dec 2006 22:38:16 GMT

Message-ID:

<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: */

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; }}