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( )