[1162] in java-interest
help with class loader
daemon@ATHENA.MIT.EDU (Michael Mills 21728)
Fri Aug 25 06:33:27 1995
From: ekim@nyquist.bellcore.com (Michael Mills 21728)
To: java-interest@java.Eng.Sun.COM
Date: Thu, 24 Aug 1995 12:35:30 -0400 (EDT)
Hi,
I am trying to learn how to download code using the class loader.
I cannot seem to figure out how to get things to work.
I have 2 problems.
1) How do you compile a java program when a referenced class is not local
2) How does the class loader work.
Here is the program I am working with. The hello class was created from a file
called Hello.java and hello.class was renamed to hello. This was to "simulate"
getting a class over a network.
This line compiles but causes a crash:
Object h = hello.newInstance();
And this one won't compile unless the hello class is available.
hello hi = new hello();
q.java:68: Class hello not found in type declaration.
hello hi = new hello();
^
q.java:68: Class hello not found in new.
hello hi = new hello();
Any help is appreciated.
Mike
import java.lang.*;
import java.io.FileInputStream;
import java.util.Hashtable;
class tstLoader extends ClassLoader {
int maxBuff = 32768;
byte[] buff = new byte[maxBuff];
static Hashtable cache = new Hashtable();
public synchronized Class loadClass( String name)
{
Class c = (Class) cache.get(name);
if( c == null )
{
System.out.println("READ BYTES" );
int index=0;
FileInputStream fin = new FileInputStream( name );
int ret = 0;
while (ret >= 0)
{
ret = fin.read(buff,index,maxBuff-index);
if( ret > 0) index += ret;
}
fin.close();
System.out.println("DEFINE CLASS" );
c = defineClass(buff,0,index);
cache.put( new String(name),c);
}
return( c );
}
public synchronized Class loadClass(String name, boolean resolve)
{
System.out.println("LOAD CLASS name,resolve" );
Class c = (Class) cache.get(name);
if(c == null)
{
System.out.println("TRY Class.forName" );
c = Class.forName(name);
if( c == null)
{
System.out.println("CLASS NOT FOUND" );
}
} else {
System.out.println("HAD Class cached" );
}
if( (c != null) && resolve )
{
System.out.println("RESOLVE");
resolveClass(c);
}
return c;
}
}
class tst
{
public static void main (String argv [])
{
tstLoader loader = new tstLoader();
// hello hi = new hello();
Class hello = loader.loadClass("hello");
Object h = hello.newInstance();
// hello hi = new hello();
}
}
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