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

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( )