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Class java.lang.Class

java.lang.Object
    |
    +----java.lang.Class

public final class Class

extends Object

implements Serializable

There is no public constructor for the class Class. Class objects are constructed automatically by the Java Virtual Machine as classes are loaded and by calls to the defineClass method in the class loader.

The following example uses a Class object to print the Class name of an object:

     void printClassName(Object obj) {
         System.out.println("The class of " + obj +
                            " is " + obj.getClass().getName());
     }
 

Since:

JDK1.0

See Also:

defineClass

forName(String)

Returns the Class object associated with the class with the given string name.

getClasses()

Returns an array containing Class objects representing all the public classes and interfaces that are members of the class represented by this Class object.

getClassLoader()

Determines the class loader for the class.

getComponentType()

If this class represents an array type, returns the Class object representing the component type of the array; otherwise returns null.

getConstructor(Class[])

Returns a Constructor object that reflects the specified public constructor of the class represented by this Class object.

getConstructors()

Returns an array containing Constructor objects reflecting all the public constructors of the class represented by this Class object.

getDeclaredClasses()

Returns an array of Class objects reflecting all the classes and interfaces declared as members of the class represented by this Class object.

getDeclaredConstructor(Class[])

Returns a Constructor object that reflects the specified declared constructor of the class or interface represented by this Class object.

getDeclaredConstructors()

Returns an array of Constructor objects reflecting all the constructors declared by the class represented by this Class object.

getDeclaredField(String)

Returns a Field object that reflects the specified declared field of the class or interface represented by this Class object.

getDeclaredFields()

Returns an array of Field objects reflecting all the fields declared by the class or interface represented by this Class object.

getDeclaredMethod(String, Class[])

Returns a Method object that reflects the specified declared method of the class or interface represented by this Class object.

getDeclaredMethods()

Returns an array of Method objects reflecting all the methods declared by the class or interface represented by this Class object.

getDeclaringClass()

If the class or interface represented by this Class object is a member of another class, returns the Class object representing the class of which it is a member (its declaring class).

getField(String)

Returns a Field object that reflects the specified public member field of the class or interface represented by this Class object.

getFields()

Returns an array containing Field objects reflecting all the accessible public fields of the class or interface represented by this Class object.

getInterfaces()

Determines the interfaces implemented by the class or interface represented by this object.

getMethod(String, Class[])

Returns a Method object that reflects the specified public member method of the class or interface represented by this Class object.

getMethods()

Returns an array containing Method objects reflecting all the public member methods of the class or interface represented by this Class object, including those declared by the class or interface and and those inherited from superclasses and superinterfaces.

getModifiers()

Returns the Java language modifiers for this class or interface, encoded in an integer.

getName()

Returns the fully-qualified name of the type (class, interface, array, or primitive) represented by this Class object, as a String.

getPackage()

Get the package for this class.

getResource(String)

getResourceAsStream(String)

Find a resource with a given name.

getSigners()

Get the signers of this class.

getSuperclass()

If this object represents any class other than the class Object, then the object that represents the superclass of that class is returned.

isArray()

If this Class object represents an array type, returns true, otherwise returns false.

isAssignableFrom(Class)

Determines if the class or interface represented by this Class object is either the same as, or is a superclass or superinterface of, the class or interface represented by the specified Class parameter.

isInstance(Object)

This method is the dynamic equivalent of the Java language instanceof operator.

isInterface()

Determines if the specified Class object represents an interface type.

isPrimitive()

Determines if the specified Class object represents a primitive Java type.

newInstance()

Creates a new instance of a class.

toString()

Converts the object to a string.

public String toString()

Converts the object to a string. The string representation is the string "class" or "interface" followed by a space and then the fully qualified name of the class. If this Class object represents a primitive type, returns the name of the primitive type.

Returns:

a string representation of this class object.

Overrides:

toString in class Object

public static Class forName(String className) throws ClassNotFoundException

Returns the Class object associated with the class with the given string name. Given the fully qualified name for a class or interface, in a form as returned by getName, this method attempts to locate, load and link the class. If it succeeds, returns the Class object representing the class. If it fails, the method throws a ClassNotFoundException.

For example, the following code fragment returns the runtime Class descriptor for the class named java.lang.Thread:

   Class t = Class.forName("java.lang.Thread")
 

Parameters:

className - the fully qualified name of the desired class.

Returns:

the Class descriptor for the class with the specified name.

Throws: ClassNotFoundException

if the class could not be found.

public Object newInstance() throws InstantiationException, IllegalAccessException

Creates a new instance of a class.

Returns:

a newly allocated instance of the class represented by this object. This is done exactly as if by a new expression with an empty argument list.

Throws: IllegalAccessException

if the class or initializer is not accessible.

Throws: InstantiationException

if an application tries to instantiate an abstract class or an interface, or if the instantiation fails for some other reason.

public boolean isInstance(Object obj)

This method is the dynamic equivalent of the Java language instanceof operator. The method returns true if the specified Object argument is non-null and can be cast to the reference type represented by this Class object without raising a ClassCastException. It returns false otherwise.

Specifically, if this Class object represents a declared class, returns true if the specified Object argument is an instance of the represented class (or of any of its subclasses); false otherwise. If this Class object represents an array class, returns true if the specified Object argument can be converted to an object of the array type by an identity conversion or by a widening reference conversion; false otherwise. If this Class object represents an interface, returns true if the class or any superclass of the specified Object argument implements this interface; false otherwise. If this Class object represents a primitive type, returns false.

Parameters:

obj - The object to check

public boolean isAssignableFrom(Class cls)

Determines if the class or interface represented by this Class object is either the same as, or is a superclass or superinterface of, the class or interface represented by the specified Class parameter. It returns true if so, false otherwise. If this Class object represents a primitive type, returns true if the specified Class parameter is exactly this Class object, false otherwise.

Specifically, this method tests whether the type represented by the specified Class parameter can be converted to the type represented by this Class object via an identity conversion or via a widening reference conversion. See The Java Language Specification, sections 5.1.1 and 5.1.4 , for details.

Throws: NullPointerException

if the specified Class parameter is null.

public boolean isInterface()

Determines if the specified Class object represents an interface type.

Returns:

true if this object represents an interface; false otherwise.

public boolean isArray()

If this Class object represents an array type, returns true, otherwise returns false.

public boolean isPrimitive()

Determines if the specified Class object represents a primitive Java type.

There are nine predefined Class objects to represent the eight primitive Java types and void. These are created by the Java Virtual Machine, and have the same names as the primitive types that they represent, namely boolean, byte, char, short, int, long, float, and double, and void.

These objects may only be accessed via the following public static final variables, and are the only Class objects for which this method returns true.

See Also:

TYPE, TYPE, TYPE, TYPE, TYPE, TYPE, TYPE, TYPE, TYPE

public String getName()

Returns the fully-qualified name of the type (class, interface, array, or primitive) represented by this Class object, as a String.

If this class object represents a class of arrays, then the internal form of the name consists of the name of the element type in Java signature format, preceded by one or more "[" characters representing the depth of array nesting. Thus:

 (new Object[3]).getClass().getName()
 

returns "[Ljava.lang.Object;" and:

 (new int[3][4][5][6][7][8][9]).getClass().getName()
 

returns "[[[[[[[I". The encoding of element type names is as follows:

 B            byte
 C            char
 D            double
 F            float
 I            int
 J            long
 Lclassname;  class or interface
 S            short
 Z            boolean
 

The class or interface name classname is given in fully qualified form as shown in the example above.

Returns:

the fully qualified name of the class or interface represented by this object.

public ClassLoader getClassLoader()

Determines the class loader for the class.

Returns:

the class loader that created the class or interface represented by this object, or null if the class was not created by a class loader.

See Also:

ClassLoader

public Class getSuperclass()

If this object represents any class other than the class Object, then the object that represents the superclass of that class is returned.

If this object is the one that represents the class Object or this object represents an interface, null is returned.

Returns:

the superclass of the class represented by this object.

public Package getPackage()

Get the package for this class. The classes classloader is used to find the package instance corresponding to this class. If the class has no classloader the set of packages loaded from CLASSPATH is searched to find the classes package. Null is returned if no package object was created by the classloader of this class.
Packages have attributes for versions and specifications only if the information was defined in the manifests that accompany the classes and if the class loader created the package instance with the attributes from the manifest.

Returns:

The package of the class. It may be null if no package information is available from the archive or codebase.

public Class[] getInterfaces()

Determines the interfaces implemented by the class or interface represented by this object.

If this object represents a class, the return value is an array containing objects representing all interfaces implemented by the class. The order of the interface objects in the array corresponds to the order of the interface names in the implements clause of the declaration of the class represented by this object.

If this object represents an interface, the array contains objects representing all interfaces extended by the interface. The order of the interface objects in the array corresponds to the order of the interface names in the extends clause of the declaration of the interface represented by this object.

If the class or interface implements no interfaces, the method returns an array of length 0.

Returns:

an array of interfaces implemented by this class.

public Class getComponentType()

If this class represents an array type, returns the Class object representing the component type of the array; otherwise returns null.

See Also:

Array

public int getModifiers()

Returns the Java language modifiers for this class or interface, encoded in an integer. The modifiers consist of the Java Virtual Machine's constants for public, protected, private, final, and interface; they should be decoded using the methods of class Modifier.

The modifier encodings are defined in The Java Virtual Machine Specification, table 4.1.

See Also:

Modifier

public Object[] getSigners()

Get the signers of this class.

public Class getDeclaringClass()

If the class or interface represented by this Class object is a member of another class, returns the Class object representing the class of which it is a member (its declaring class). Returns null if this class or interface is not a member of any other class.

public Class[] getClasses()

Returns an array containing Class objects representing all the public classes and interfaces that are members of the class represented by this Class object. This includes public class and interface members inherited from superclasses and public class and interface members declared by the class. Returns an array of length 0 if the class has no public member classes or interfaces, or if this Class object represents a primitive type.

public Field[] getFields() throws SecurityException

Returns an array containing Field objects reflecting all the accessible public fields of the class or interface represented by this Class object. Returns an array of length 0 if the class or interface has no accessible public fields, or if it represents an array type or a primitive type.

Specifically, if this Class object represents a class, returns the public fields of this class and of all its superclasses. If this Class object represents an interface, returns the fields of this interface and of all its superinterfaces. If this Class object represents an array type or a primitive type, returns an array of length 0.

The implicit length field for array types is not reflected by this method. User code should use the methods of class Array to manipulate arrays.

See The Java Language Specification, sections 8.2 and 8.3.

Throws: SecurityException

if access to the information is denied.

See Also:

Field

public Method[] getMethods() throws SecurityException

Returns an array containing Method objects reflecting all the public member methods of the class or interface represented by this Class object, including those declared by the class or interface and and those inherited from superclasses and superinterfaces. Returns an array of length 0 if the class or interface has no public member methods.

See The Java Language Specification, sections 8.2 and 8.4.

Throws: SecurityException

if access to the information is denied.

See Also:

Method

public Constructor[] getConstructors() throws SecurityException

Returns an array containing Constructor objects reflecting all the public constructors of the class represented by this Class object. An array of length 0 is returned if the class has no public constructors.

Throws: SecurityException

if access to the information is denied.

See Also:

Constructor

public Field getField(String name) throws NoSuchFieldException, SecurityException

Returns a Field object that reflects the specified public member field of the class or interface represented by this Class object. The name parameter is a String specifying the simple name of the desired field.

The field to be reflected is located by searching all the member fields of the class or interface represented by this Class object for a public field with the specified name.

See The Java Language Specification, sections 8.2 and 8.3.

Throws: NoSuchFieldException

if a field with the specified name is not found.

Throws: SecurityException

if access to the information is denied.

See Also:

Field

public Method getMethod(String name,
                        Class[] parameterTypes) throws NoSuchMethodException, SecurityException

Returns a Method object that reflects the specified public member method of the class or interface represented by this Class object. The name parameter is a String specifying the simple name the desired method, and the parameterTypes parameter is an array of Class objects that identify the method's formal parameter types, in declared order.

The method to reflect is located by searching all the member methods of the class or interface represented by this Class object for a public method with the specified name and exactly the same formal parameter types.

See The Java Language Specification, sections 8.2 and 8.4.

Throws: NoSuchMethodException

if a matching method is not found.

Throws: SecurityException

if access to the information is denied.

See Also:

Method

public Constructor getConstructor(Class[] parameterTypes) throws NoSuchMethodException, SecurityException

Returns a Constructor object that reflects the specified public constructor of the class represented by this Class object. The parameterTypes parameter is an array of Class objects that identify the constructor's formal parameter types, in declared order.

The constructor to reflect is located by searching all the constructors of the class represented by this Class object for a public constructor with the exactly the same formal parameter types.

Throws: NoSuchMethodException

if a matching method is not found.

Throws: SecurityException

if access to the information is denied.

See Also:

Constructor

public Class[] getDeclaredClasses() throws SecurityException

Returns an array of Class objects reflecting all the classes and interfaces declared as members of the class represented by this Class object. This includes public, protected, default (package) access, and private classes and interfaces declared by the class, but excludes inherited classes and interfaces. Returns an array of length 0 if the class declares no classes or interfaces as members, or if this Class object represents a primitive type.

Throws: SecurityException

if access to the information is denied.

public Field[] getDeclaredFields() throws SecurityException

Returns an array of Field objects reflecting all the fields declared by the class or interface represented by this Class object. This includes public, protected, default (package) access, and private fields, but excludes inherited fields. Returns an array of length 0 if the class or interface declares no fields, or if this Class object represents a primitive type. See The Java Language Specification, sections 8.2 and 8.3.

Throws: SecurityException

if access to the information is denied.

See Also:

Field

public Method[] getDeclaredMethods() throws SecurityException

Returns an array of Method objects reflecting all the methods declared by the class or interface represented by this Class object. This includes public, protected, default (package) access, and private methods, but excludes inherited methods. Returns an array of length 0 if the class or interface declares no methods, or if this Class object represents a primitive type.

See The Java Language Specification, section 8.2.

Throws: SecurityException

if access to the information is denied.

See Also:

Method

public Constructor[] getDeclaredConstructors() throws SecurityException

Returns an array of Constructor objects reflecting all the constructors declared by the class represented by this Class object. These are public, protected, default (package) access, and private constructors. Returns an array of length 0 if this Class object represents an interface or a primitive type.

See The Java Language Specification, section 8.2.

Throws: SecurityException

if access to the information is denied.

See Also:

Constructor

public Field getDeclaredField(String name) throws NoSuchFieldException, SecurityException

Returns a Field object that reflects the specified declared field of the class or interface represented by this Class object. The name parameter is a String that specifies the simple name of the desired field.

Throws: NoSuchFieldException

if a field with the specified name is not found.

Throws: SecurityException

if access to the information is denied.

See Also:

Field

public Method getDeclaredMethod(String name,
                                Class[] parameterTypes) throws NoSuchMethodException, SecurityException

Returns a Method object that reflects the specified declared method of the class or interface represented by this Class object. The name parameter is a String that specifies the simple name of the desired method, and the parameterTypes parameter is an array of Class objects that identify the method's formal parameter types, in declared order.

Throws: NoSuchMethodException

if a matching method is not found.

Throws: SecurityException

if access to the information is denied.

See Also:

Method

public Constructor getDeclaredConstructor(Class[] parameterTypes) throws NoSuchMethodException, SecurityException

Returns a Constructor object that reflects the specified declared constructor of the class or interface represented by this Class object. The parameterTypes parameter is an array of Class objects that identify the constructor's formal parameter types, in declared order.

Throws: NoSuchMethodException

if a matching method is not found.

Throws: SecurityException

if access to the information is denied.

See Also:

Constructor

public InputStream getResourceAsStream(String name)

Find a resource with a given name. Will return null if no resource with this name is found. The rules for searching a resources associated with a given class are implemented by the ClassLoader of the class.

The Class methods delegate to ClassLoader methods, after applying a naming convention: if the resource name starts with "/", it is used as is. Otherwise, the name of the package is prepended, after converting "." to "/".

See Also:

ClassLoader

public URL getResource(String name)

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