java.lang.ClassLoader
Every Class
object contains a reference to the ClassLoader
that defined it (§20.3.7). Whenever executable Java code needs to use a class that has not yet been loaded, the loadClass
method is invoked for the class loader of the class containing the code in question.
Class objects for array classes are not created by class loaders, but are created automatically as required by the Java runtime. The class loader for an array class, as returned by the getClassLoader
method of class Class
(§20.3.7), is the same as the class loader for its element type; if the element type is a primitive type, then the array class has no class loader.
Class loaders may typically be used by security managers (§20.17) to indicate security domains: two classes may considered to be "friendly" or "related" to each other only if they were defined by the same class loader.
public abstract classClassLoader
{ protectedClassLoader
() throws SecurityException; protected abstract ClassloadClass
(String name, boolean resolve)
throws ClassNotFoundException; protected final ClassdefineClass
(byte data[], int offset, int length)
throws NullPointerException, IndexOutOfBoundsException, ClassFormatError; protected final voidresolveClass
(Class c)
throws NullPointerException; protected final ClassfindSystemClass
(String name)
throws ClassNotFoundException; }
20.14.1 protected
ClassLoader
() throws SecurityException
This constructor is invoked for every newly created class loader. Because the class
ClassLoader
is abstract
, it is not possible to create a new instance of the class
ClassLoader
itself; however, every constructor for a subclass of ClassLoader
necessarily invokes this constructor, explicitly or implicitly, directly or indirectly.
All this constructor does is to enforce a security check: if there is a security manager, its checkCreateClassLoader
method (§20.17.10) is called.
20.14.2 protected abstract Class
loadClass
(String name,
boolean link)
throws ClassNotFoundException
Every subclass of ClassLoader
that is not itself abstract must provide an implementation
of the method loadClass
.
The general contract of loadClass
is that, given the name
of a class, it either returns the Class
object for the class or throws a ClassNotFoundException
.
If a Class
object is to be returned and link
is true
, then the Class
object should be linked (§12.3, §20.14.4) before it is returned.
In most cases, it is wise for a subclass of ClassLoader
(§20.14) to implement the loadClass
method as a synchronized
method.
20.14.3 protected final Class
defineClass
(byte data[],
int offset, int length)
throws NullPointerException, IndexOutOfBoundsException, ClassFormatError
This method may be used by a class loader to define a new class.
The bytes in the array data
in positions offset
through offset+length-1
should have the format of a valid class file as defined by the Java Virtual Machine Specification.
If data
is null
, then a NullPointerException
is thrown.
An IndexOutOfBoundsException
is thrown if any of the following are true:
If the indicated bytes of
data
do not constitute a valid class definition, then a ClassFormatError
is thrown. Otherwise, this method creates and returns a Class
object as described by the data bytes20.14.4 protected final void
resolveClass
(Class c)
throws NullPointerException
This (misleadingly named) method may be used by a class loader to link (§12.3, §20.14.4) a class.
If c
is null
, then a NullPointerException
is thrown.
If the Class
object c
has already been linked, then this method simply returns.
Otherwise, the class is linked as described in §12.3.
20.14.5 protected final Class
findSystemClass
(String name)
throws ClassNotFoundException
This method may be used by a class loader to locate a class that has no class
loader. This includes built-in classes such as java.lang.Object
, as well as
classes that the host implementation may keep in, for example, a local file system.
Given the name
of a class, this method, like the loadClass
method, either returns the Class
object for the class or throws a ClassNotFoundException
.
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Java Language Specification (HTML generated by Suzette Pelouch on February 24, 1998)
Copyright © 1996 Sun Microsystems, Inc.
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