java.lang

Class Class

Implemented Interfaces:
Serializable

public final class Class
extends Object
implements Serializable

A Class represents a Java type. There will never be multiple Class objects with identical names and ClassLoaders. Primitive types, array types, and void also have a Class object.

Arrays with identical type and number of dimensions share the same class. The array class ClassLoader is the same as the ClassLoader of the element type of the array (which can be null to indicate the bootstrap classloader). The name of an array class is [<signature format>;.

For example, String[]'s class is [Ljava.lang.String;. boolean, byte, short, char, int, long, float and double have the "type name" of Z,B,S,C,I,J,F,D for the purposes of array classes. If it's a multidimensioned array, the same principle applies: int[][][] == [[[I.

There is no public constructor - Class objects are obtained only through the virtual machine, as defined in ClassLoaders.

Since:
1.0
See Also:
ClassLoader, Serialized Form

Method Summary

boolean
desiredAssertionStatus()
Returns the desired assertion status of this class, if it were to be initialized at this moment.
static Class
forName(String name)
Use the classloader of the current class to load, link, and initialize a class.
static Class
forName(String name, boolean initialize, ClassLoader classloader)
Use the specified classloader to load and link a class.
ClassLoader
getClassLoader()
Get the ClassLoader that loaded this class.
Class[]
getClasses()
Get all the public member classes and interfaces declared in this class or inherited from superclasses.
Class
getComponentType()
If this is an array, get the Class representing the type of array.
Constructor
getConstructor(Class[] types)
Get a public constructor declared in this class.
Constructor[]
getConstructors()
Get all the public constructors of this class.
Class[]
getDeclaredClasses()
Get all the declared member classes and interfaces in this class, but not those inherited from superclasses.
Constructor
getDeclaredConstructor(Class[] types)
Get a constructor declared in this class.
Constructor[]
getDeclaredConstructors()
Get all the declared constructors of this class.
Field
getDeclaredField(String name)
Get a field declared in this class, where name is its simple name.
Field[]
getDeclaredFields()
Get all the declared fields in this class, but not those inherited from superclasses.
Method
getDeclaredMethod(String methodName, Class[] types)
Get a method declared in this class, where name is its simple name.
Method[]
getDeclaredMethods()
Get all the declared methods in this class, but not those inherited from superclasses.
Class
getDeclaringClass()
If this is a nested or inner class, return the class that declared it.
Field
getField(String fieldName)
Get a public field declared or inherited in this class, where name is its simple name.
Field[]
getFields()
Get all the public fields declared in this class or inherited from superclasses.
Class[]
getInterfaces()
Get the interfaces this class directly implements, in the order that they were declared.
Method
getMethod(String methodName, Class[] types)
Get a public method declared or inherited in this class, where name is its simple name.
Method[]
getMethods()
Get all the public methods declared in this class or inherited from superclasses.
int
getModifiers()
Get the modifiers of this class.
String
getName()
Get the name of this class, separated by dots for package separators.
Package
getPackage()
Returns the Package in which this class is defined Returns null when this information is not available from the classloader of this class.
ProtectionDomain
getProtectionDomain()
Returns the protection domain of this class.
URL
getResource(String resourceName)
Get a resource URL using this class's package using the getClassLoader().getResource() method.
InputStream
getResourceAsStream(String resourceName)
Get a resource using this class's package using the getClassLoader().getResourceAsStream() method.
Object[]
getSigners()
Get the signers of this class.
Class
getSuperclass()
Get the direct superclass of this class.
boolean
isArray()
Return whether this class is an array type.
boolean
isAssignableFrom(Class c)
Discover whether an instance of the Class parameter would be an instance of this Class as well.
boolean
isInstance(Object o)
Discover whether an Object is an instance of this Class.
boolean
isInterface()
Check whether this class is an interface or not.
boolean
isPrimitive()
Return whether this class is a primitive type.
Object
newInstance()
Get a new instance of this class by calling the no-argument constructor.
String
toString()
Return the human-readable form of this Object.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Details

desiredAssertionStatus

public boolean desiredAssertionStatus()
Returns the desired assertion status of this class, if it were to be initialized at this moment. The class assertion status, if set, is returned; the backup is the default package status; then if there is a class loader, that default is returned; and finally the system default is returned. This method seldom needs calling in user code, but exists for compilers to implement the assert statement. Note that there is no guarantee that the result of this method matches the class's actual assertion status.
Returns:
the desired assertion status
Since:
1.4

forName

public static Class forName(String name)
            throws ClassNotFoundException
Use the classloader of the current class to load, link, and initialize a class. This is equivalent to your code calling Class.forName(name, true, getClass().getClassLoader()).
Parameters:
name - the name of the class to find
Returns:
the Class object representing the class
Throws:
ClassNotFoundException - if the class was not found by the classloader

forName

public static Class forName(String name,
                            boolean initialize,
                            ClassLoader classloader)
            throws ClassNotFoundException
Use the specified classloader to load and link a class. If the loader is null, this uses the bootstrap class loader (provide the security check succeeds). Unfortunately, this method cannot be used to obtain the Class objects for primitive types or for void, you have to use the fields in the appropriate java.lang wrapper classes.

Calls classloader.loadclass(name, initialize).

Parameters:
name - the name of the class to find
initialize - whether or not to initialize the class at this time
classloader - the classloader to use to find the class; null means to use the bootstrap class loader
Returns:
the class object for the given class
Throws:
ClassNotFoundException - if the class was not found by the classloader
SecurityException - if the classloader argument is null and the caller does not have the RuntimePermission("getClassLoader") permission
Since:
1.2
See Also:
ClassLoader

getClassLoader

public ClassLoader getClassLoader()
Get the ClassLoader that loaded this class. If the class was loaded by the bootstrap classloader, this method will return null. If there is a security manager, and the caller's class loader is not an ancestor of the requested one, a security check of RuntimePermission("getClassLoader") must first succeed. Primitive types and void return null.
Returns:
the ClassLoader that loaded this class
Throws:
SecurityException - if the security check fails

getClasses

public Class[] getClasses()
Get all the public member classes and interfaces declared in this class or inherited from superclasses. This returns an array of length 0 if there are no member classes, including for primitive types. A security check may be performed, with checkMemberAccess(this, Member.PUBLIC) as well as checkPackageAccess both having to succeed.
Returns:
all public member classes in this class
Throws:
SecurityException - if the security check fails
Since:
1.1

getComponentType

public Class getComponentType()
If this is an array, get the Class representing the type of array. Examples: "[[Ljava.lang.String;" would return "[Ljava.lang.String;", and calling getComponentType on that would give "java.lang.String". If this is not an array, returns null.
Returns:
the array type of this class, or null
Since:
1.1
See Also:
Array

getConstructor

public Constructor getConstructor(Class[] types)
            throws NoSuchMethodException
Get a public constructor declared in this class. If the constructor takes no argument, an array of zero elements and null are equivalent for the types argument. A security check may be performed, with checkMemberAccess(this, Member.PUBLIC) as well as checkPackageAccess both having to succeed.
Parameters:
types - the type of each parameter
Returns:
the constructor
Throws:
NoSuchMethodException - if the constructor does not exist
SecurityException - if the security check fails
Since:
1.1

getConstructors

public Constructor[] getConstructors()
Get all the public constructors of this class. This returns an array of length 0 if there are no constructors, including for primitive types, arrays, and interfaces. It does, however, include the default constructor if one was supplied by the compiler. A security check may be performed, with checkMemberAccess(this, Member.PUBLIC) as well as checkPackageAccess both having to succeed.
Returns:
all public constructors in this class
Throws:
SecurityException - if the security check fails
Since:
1.1

getDeclaredClasses

public Class[] getDeclaredClasses()
Get all the declared member classes and interfaces in this class, but not those inherited from superclasses. This returns an array of length 0 if there are no member classes, including for primitive types. A security check may be performed, with checkMemberAccess(this, Member.DECLARED) as well as checkPackageAccess both having to succeed.
Returns:
all declared member classes in this class
Throws:
SecurityException - if the security check fails
Since:
1.1

getDeclaredConstructor

public Constructor getDeclaredConstructor(Class[] types)
            throws NoSuchMethodException
Get a constructor declared in this class. If the constructor takes no argument, an array of zero elements and null are equivalent for the types argument. A security check may be performed, with checkMemberAccess(this, Member.DECLARED) as well as checkPackageAccess both having to succeed.
Parameters:
types - the type of each parameter
Returns:
the constructor
Throws:
NoSuchMethodException - if the constructor does not exist
SecurityException - if the security check fails
Since:
1.1

getDeclaredConstructors

public Constructor[] getDeclaredConstructors()
Get all the declared constructors of this class. This returns an array of length 0 if there are no constructors, including for primitive types, arrays, and interfaces. It does, however, include the default constructor if one was supplied by the compiler. A security check may be performed, with checkMemberAccess(this, Member.DECLARED) as well as checkPackageAccess both having to succeed.
Returns:
all constructors in this class
Throws:
SecurityException - if the security check fails
Since:
1.1

getDeclaredField

public Field getDeclaredField(String name)
            throws NoSuchFieldException
Get a field declared in this class, where name is its simple name. The implicit length field of arrays is not available. A security check may be performed, with checkMemberAccess(this, Member.DECLARED) as well as checkPackageAccess both having to succeed.
Parameters:
name - the name of the field
Returns:
the field
Throws:
NoSuchFieldException - if the field does not exist
SecurityException - if the security check fails
Since:
1.1

getDeclaredFields

public Field[] getDeclaredFields()
Get all the declared fields in this class, but not those inherited from superclasses. This returns an array of length 0 if there are no fields, including for primitive types. This does not return the implicit length field of arrays. A security check may be performed, with checkMemberAccess(this, Member.DECLARED) as well as checkPackageAccess both having to succeed.
Returns:
all declared fields in this class
Throws:
SecurityException - if the security check fails
Since:
1.1

getDeclaredMethod

public Method getDeclaredMethod(String methodName,
                                Class[] types)
            throws NoSuchMethodException
Get a method declared in this class, where name is its simple name. The implicit methods of Object are not available from arrays or interfaces. Constructors (named "<init>" in the class file) and class initializers (name "<clinit>") are not available. The Virtual Machine allows multiple methods with the same signature but differing return types; in such a case the most specific return types are favored, then the final choice is arbitrary. If the method takes no argument, an array of zero elements and null are equivalent for the types argument. A security check may be performed, with checkMemberAccess(this, Member.DECLARED) as well as checkPackageAccess both having to succeed.
Parameters:
methodName - the name of the method
types - the type of each parameter
Returns:
the method
Throws:
NoSuchMethodException - if the method does not exist
SecurityException - if the security check fails
Since:
1.1

getDeclaredMethods

public Method[] getDeclaredMethods()
Get all the declared methods in this class, but not those inherited from superclasses. This returns an array of length 0 if there are no methods, including for primitive types. This does include the implicit methods of arrays and interfaces which mirror methods of Object, nor does it include constructors or the class initialization methods. The Virtual Machine allows multiple methods with the same signature but differing return types; all such methods are in the returned array. A security check may be performed, with checkMemberAccess(this, Member.DECLARED) as well as checkPackageAccess both having to succeed.
Returns:
all declared methods in this class
Throws:
SecurityException - if the security check fails
Since:
1.1

getDeclaringClass

public Class getDeclaringClass()
If this is a nested or inner class, return the class that declared it. If not, return null.
Returns:
the declaring class of this class
Since:
1.1

getField

public Field getField(String fieldName)
            throws NoSuchFieldException
Get a public field declared or inherited in this class, where name is its simple name. If the class contains multiple accessible fields by that name, an arbitrary one is returned. The implicit length field of arrays is not available. A security check may be performed, with checkMemberAccess(this, Member.PUBLIC) as well as checkPackageAccess both having to succeed.
Parameters:
fieldName - the name of the field
Returns:
the field
Throws:
NoSuchFieldException - if the field does not exist
SecurityException - if the security check fails
Since:
1.1
See Also:
getFields()

getFields

public Field[] getFields()
Get all the public fields declared in this class or inherited from superclasses. This returns an array of length 0 if there are no fields, including for primitive types. This does not return the implicit length field of arrays. A security check may be performed, with checkMemberAccess(this, Member.PUBLIC) as well as checkPackageAccess both having to succeed.
Returns:
all public fields in this class
Throws:
SecurityException - if the security check fails
Since:
1.1

getInterfaces

public Class[] getInterfaces()
Get the interfaces this class directly implements, in the order that they were declared. This returns an empty array, not null, for Object, primitives, void, and classes or interfaces with no direct superinterface. Array types return Cloneable and Serializable.
Returns:
the interfaces this class directly implements

getMethod

public Method getMethod(String methodName,
                        Class[] types)
            throws NoSuchMethodException
Get a public method declared or inherited in this class, where name is its simple name. The implicit methods of Object are not available from interfaces. Constructors (named "<init>" in the class file) and class initializers (name "<clinit>") are not available. The Virtual Machine allows multiple methods with the same signature but differing return types, and the class can inherit multiple methods of the same return type; in such a case the most specific return types are favored, then the final choice is arbitrary. If the method takes no argument, an array of zero elements and null are equivalent for the types argument. A security check may be performed, with checkMemberAccess(this, Member.PUBLIC) as well as checkPackageAccess both having to succeed.
Parameters:
methodName - the name of the method
types - the type of each parameter
Returns:
the method
Throws:
NoSuchMethodException - if the method does not exist
SecurityException - if the security check fails
Since:
1.1
See Also:
getMethods()

getMethods

public Method[] getMethods()
Get all the public methods declared in this class or inherited from superclasses. This returns an array of length 0 if there are no methods, including for primitive types. This does not include the implicit methods of interfaces which mirror methods of Object, nor does it include constructors or the class initialization methods. The Virtual Machine allows multiple methods with the same signature but differing return types; all such methods are in the returned array. A security check may be performed, with checkMemberAccess(this, Member.PUBLIC) as well as checkPackageAccess both having to succeed.
Returns:
all public methods in this class
Throws:
SecurityException - if the security check fails
Since:
1.1

getModifiers

public int getModifiers()
Get the modifiers of this class. These can be decoded using Modifier, and is limited to one of public, protected, or private, and any of final, static, abstract, or interface. An array class has the same public, protected, or private modifier as its component type, and is marked final but not an interface. Primitive types and void are marked public and final, but not an interface.
Returns:
the modifiers of this class
Since:
1.1
See Also:
Modifier

getName

public String getName()
Get the name of this class, separated by dots for package separators. If the class represents a primitive type, or void, then the name of the type as it appears in the Java programming language is returned. For instance, Byte.TYPE.getName() returns "byte". Arrays are specially encoded as shown on this table.
 array type          [element type
                     (note that the element type is encoded per
                      this table)
 boolean             Z
 byte                B
 char                C
 short               S
 int                 I
 long                J
 float               F
 double              D
 void                V
 class or interface, alone: <dotted name>
 class or interface, as element type: L<dotted name>;
 
Returns:
the name of this class

getPackage

public Package getPackage()
Returns the Package in which this class is defined Returns null when this information is not available from the classloader of this class.
Returns:
the package for this class, if it is available
Since:
1.2

getProtectionDomain

public ProtectionDomain getProtectionDomain()
Returns the protection domain of this class. If the classloader did not record the protection domain when creating this class the unknown protection domain is returned which has a null code source and all permissions. A security check may be performed, with RuntimePermission("getProtectionDomain").
Returns:
the protection domain
Throws:
SecurityException - if the security manager exists and the caller does not have RuntimePermission("getProtectionDomain").
Since:
1.2

getResource

public URL getResource(String resourceName)
Get a resource URL using this class's package using the getClassLoader().getResource() method. If this class was loaded using the system classloader, ClassLoader.getSystemResource() is used instead.

If the name you supply is absolute (it starts with a /), then the leading / is removed and it is passed on to getResource(). If it is relative, the package name is prepended, and .'s are replaced with /.

The URL returned is system- and classloader-dependent, and could change across implementations.

Parameters:
resourceName - the name of the resource, generally a path
Returns:
the URL to the resource
Throws:
NullPointerException - if name is null
Since:
1.1

getResourceAsStream

public InputStream getResourceAsStream(String resourceName)
Get a resource using this class's package using the getClassLoader().getResourceAsStream() method. If this class was loaded using the system classloader, ClassLoader.getSystemResource() is used instead.

If the name you supply is absolute (it starts with a /), then the leading / is removed and it is passed on to getResource(). If it is relative, the package name is prepended, and .'s are replaced with /.

The URL returned is system- and classloader-dependent, and could change across implementations.

Parameters:
resourceName - the name of the resource, generally a path
Returns:
an InputStream with the contents of the resource in it, or null
Throws:
NullPointerException - if name is null
Since:
1.1

getSigners

public Object[] getSigners()
Get the signers of this class. This returns null if there are no signers, such as for primitive types or void.
Returns:
the signers of this class
Since:
1.1

getSuperclass

public Class getSuperclass()
Get the direct superclass of this class. If this is an interface, Object, a primitive type, or void, it will return null. If this is an array type, it will return Object.
Returns:
the direct superclass of this class

isArray

public boolean isArray()
Return whether this class is an array type.
Returns:
whether this class is an array type
Since:
1.1

isAssignableFrom

public boolean isAssignableFrom(Class c)
Discover whether an instance of the Class parameter would be an instance of this Class as well. Think of doing isInstance(c.newInstance()) or even c.newInstance() instanceof (this class). While this checks widening conversions for objects, it must be exact for primitive types.
Parameters:
c - the class to check
Returns:
whether an instance of c would be an instance of this class as well
Throws:
NullPointerException - if c is null
Since:
1.1

isInstance

public boolean isInstance(Object o)
Discover whether an Object is an instance of this Class. Think of it as almost like o instanceof (this class).
Parameters:
o - the Object to check
Returns:
whether o is an instance of this class
Since:
1.1

isInterface

public boolean isInterface()
Check whether this class is an interface or not. Array types are not interfaces.
Returns:
whether this class is an interface or not

isPrimitive

public boolean isPrimitive()
Return whether this class is a primitive type. A primitive type class is a class representing a kind of "placeholder" for the various primitive types, or void. You can access the various primitive type classes through java.lang.Boolean.TYPE, java.lang.Integer.TYPE, etc., or through boolean.class, int.class, etc.
Returns:
whether this class is a primitive type
Since:
1.1

newInstance

public Object newInstance()
            throws InstantiationException,
                   IllegalAccessException
Get a new instance of this class by calling the no-argument constructor. The class is initialized if it has not been already. A security check may be performed, with checkMemberAccess(this, Member.PUBLIC) as well as checkPackageAccess both having to succeed.
Returns:
a new instance of this class
Throws:
InstantiationException - if there is not a no-arg constructor for this class, including interfaces, abstract classes, arrays, primitive types, and void; or if an exception occurred during the constructor
IllegalAccessException - if you are not allowed to access the no-arg constructor because of scoping reasons
SecurityException - if the security check fails

toString

public String toString()
Return the human-readable form of this Object. For an object, this is either "interface " or "class " followed by getName(), for primitive types and void it is just getName().
Overrides:
toString in interface Object
Returns:
the human-readable form of this Object

Class.java -- Representation of a Java class. Copyright (C) 1998, 1999, 2000, 2002, 2003, 2004, 2005 Free Software Foundation This file is part of GNU Classpath. GNU Classpath is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU Classpath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Classpath; see the file COPYING. If not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. Linking this library statically or dynamically with other modules is making a combined work based on this library. Thus, the terms and conditions of the GNU General Public License cover the whole combination. As a special exception, the copyright holders of this library give you permission to link this library with independent modules to produce an executable, regardless of the license terms of these independent modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.