Java in a Nutshell, 5th Edition [Electronic resources] نسخه متنی

This class is the abstract
superclass of objects that know how to load Java classes into a Java
VM. Given a ClassLoader object, you can
dynamically load a class by calling the public loadClass(
) method, specifying the full name of the desired class.
You can obtain a resource associated with a class by calling
getresource( ), geTResources(
), and getresourceAsStream( ).
Many applications do not need to use
ClassLoader directly; these applications use the
Class.forName( ) and Class.getResource(
) methods to dynamically load classes and resources using
the ClassLoader object that loaded the application
itself.

In order to load classes over the
network or from any source other than the class path, you must use a
custom ClassLoader object that knows how to obtain
data from that source. A java.net.URLClassLoader
is suitable for this purpose for almost all applications. Only rarely
should an application need to define a ClassLoader
subclass of its own. When this is necessary, the subclass should
typically extend java.security.SecureClassLoader
and override the findClass( ) method. This method
must find the bytes that comprise the named class, then pass them to
the defineClass( ) method and return the resulting
Class object. In Java 1.2 and later, the
findClass( ) method must also
define the Package
object associated with the class, if it has not already been defined.
It can use getPackage( ) and
definePackage( ) for this purpose. Custom
subclasses of ClassLoader should also override
findResource( ) and findResources(
) to enable the public geTResource( )
and getresources( ) methods.

In Java 1.4 and later you can specify whether the
classes
loaded through a ClassLoader should have
assertions
(assert statements) enabled.
setDefaultAssertionStatus(
) enables or disables assertions for all loaded
classes. setPackageAssertionStatus(
) and setClassAssertionStatus(
) allow you to override the default assertion
status for a named
package or a named class.
Finally, clearAssertionStatus(
) sets the default status to
false and discards the assertions status for any
named packages and classes.

public abstract class

ClassLoader {
// Protected Constructors
protected

ClassLoader ( );

1.2 protected

ClassLoader (ClassLoader

parent );
// Public Class Methods

1.2 public static ClassLoader

getSystemClassLoader ( );

1.1 public static java.net.URL

getSystemResource (String

name );

1.1 public static java.io.InputStream

getSystemResourceAsStream (String

name );

1.2 public static java.util.Enumeration<java.net.URL>

getSystemResources (String

name )
throws java.io.IOException;
// Public Instance Methods

1.4 public void

clearAssertionStatus ( ); synchronized

1.2 public final ClassLoader

getParent ( );

1.1 public java.net.URL

getResource (String

name );

1.1 public java.io.InputStream

getResourceAsStream (String

name );

1.2 public java.util.Enumeration<java.net.URL>

getResources (String

name ) throws
java.io.IOException;

1.1 public Class<?>

loadClass (String

name ) throws ClassNotFoundException;

1.4 public void

setClassAssertionStatus (String

className , boolean

enabled ); synchronized

1.4 public void

setDefaultAssertionStatus (boolean

enabled ); synchronized

1.4 public void

setPackageAssertionStatus (String

packageName , boolean

enabled ); synchronized
// Protected Instance Methods

5.0 protected final Class<?>

defineClass (String

name , java.nio.ByteBuffer

b ,
java.security.ProtectionDomain protectionDomain)
throws ClassFormatError;

1.1 protected final Class<?>

defineClass (String

name , byte[ ]

b , int

off , int

len )
throws ClassFormatError;

1.2 protected final Class<?>

defineClass (String

name , byte[ ]

b , int

off , int

len ,
java.security.ProtectionDomain

protectionDomain )
throws ClassFormatError;

1.2 protected Package

definePackage (String

name , String

specTitle , String

specVersion ,
String

specVendor , String

implTitle , String

implVersion , String

implVendor , java.net.URL

sealBase )
throws IllegalArgumentException;

1.2 protected Class<?>

findClass (String

name ) throws ClassNotFoundException;

1.2 protected String

findLibrary (String

libname ); constant

1.1 protected final Class<?>

findLoadedClass (String

name );

1.2 protected java.net.URL

findResource (String

name ); constant

1.2 protected java.util.Enumeration<java.net.URL>

findResources (String

name ) throws
java.io.IOException;
protected final Class<?>

findSystemClass (String

name ) throws ClassNotFoundException;

1.2 protected Package

getPackage (String

name );

1.2 protected Package[ ]

getPackages ( );
protected Class<?>

loadClass (String

name , boolean

resolve )
throws ClassNotFoundException; synchronized
protected final void

resolveClass (Class<?>

c );

1.1 protected final void

setSigners (Class<?>

c , Object[ ]

signers );
// Deprecated Protected Methods

# protected final Class<?>

defineClass (byte[ ]

b , int

off , int

len ) throws ClassFormatError;
}

Subclasses

java.security.SecureClassLoader

Passed To

Class.forName( ),
THRead.setContextClassLoader( ),
java.lang.instrument.ClassFileTransformer.transform(
),
java.lang.instrument.Instrumentation.getInitiatedClasses(
), java.lang.reflect.Proxy.{getProxyClass(
), newProxyInstance( )},
java.net.URLClassLoader.{newInstance( ),
URLClassLoader( )},
java.security.ProtectionDomain.ProtectionDomain(
),
java.security.SecureClassLoader.SecureClassLoader(
), java.util.ResourceBundle.getBundle( )

Returned By

Class.getClassLoader( ),
SecurityManager.currentClassLoader( ),
Thread.getContextClassLoader( ),
java.security.ProtectionDomain.getClassLoader( )