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Class java.lang.Class

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

public final class Class

extends Object

implements Serializable

There are no public constructors for the class Class. The Java Virtual Machine automatically constructs Class objects as classes are loaded; such objects cannot be created by user programs.

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());
	}
 

forName(String)

Given the fully-qualified name for a class or interface, this method attempts to locate, load and link the 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.

getClassLoader()

Returns the class loader that loaded this 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()

Returns an array of classes representing the interfaces of the class or interface represented by this Class 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.

getResourceAsName(String)

getResourceAsStream(String)

Find a resource with a given name.

getSigners()

Get the signers of this class.

getSuperclass()

If this Class object represents a class other than Object, returns the Class that represents the superclass of the class.

isArray()

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

isAssignableFrom(Class)

Informally, this method tests whether 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()

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

isPrimitive()

If this Class object represents a primitive Java type, returns true; otherwise returns false.

newInstance()

Attempts to create and initialize a new instance of the class represented by this Class object, provided it represents an instantiable class (whether a declared class or an array class).

toString()

If this Class object represents a class (which may be a declared class or an array class), returns a string consisting of the word "class", a space, and the fully-qualified name of the class.

  public String toString()

If this Class object represents a class (which may be a declared class or an array class), returns a string consisting of the word "class", a space, and the fully-qualified name of the class. If this Class object represents an interface, returns a String consisting of the word "interface", followed by a space, followed by the fully-qualified name of the interface. If this Class object represents a primitive type, returns the name of the primitive type.

Overrides:

toString in class Object

  public static Class forName(String className) throws ClassNotFoundException

Given the fully-qualified name for a class or interface, 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 object for the class named java.lang.Thread:

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

Note that Class objects that represent primitive types cannot be obtained via this method.

Parameters:

className - the fully-qualified name of the desired class

Returns:

the Class object for the named class

Throws: ClassNotFoundException

If the Class could not be found.

  public Object newInstance() throws InstantiationException, IllegalAccessException

Attempts to create and initialize a new instance of the class represented by this Class object, provided it represents an instantiable class (whether a declared class or an array class). If successful, returns the newly created and initialized instance.

Returns:

the new instance of this class.

Throws: InstantiationException

If you try to instantiate an abstract class or an interface or a primitive type, or if the instantiation fails for some other reason.

Throws: IllegalAccessException

If the class or initializer is not accessible.

  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)

Informally, this method tests whether 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.

The method throws a NullPointerException if the specified Class parameter is null.

  public boolean isInterface()

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

  public boolean isArray()

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

  public boolean isPrimitive()

If this Class object represents a primitive Java type, returns true; otherwise returns false.

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.

  public ClassLoader getClassLoader()

Returns the class loader that loaded this Class. Returns null if this Class was not loaded by a class loader.

See Also:

ClassLoader

  public Class getSuperclass()

If this Class object represents a class other than Object, returns the Class that represents the superclass of the class. Returns null if this Class represents the class Object, or if it represents an interface or a primitive type.

  public Class[] getInterfaces()

Returns an array of classes representing the interfaces of the class or interface represented by this Class object. If this Class object represents a class, returns an array containing objects representing the interfaces directly implemented by this class. If this Class object represents an interface, returns an array containing the direct superinterfaces of this interface.

Returns an array of length 0 if this Class object represents a class that implements no interfaces or if it represents a primitive type.

  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.

The method throws a SecurityException if access to this information is denied.

See The Java Language Specification, sections 8.2 and 8.3.

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.

The method throws a SecurityException if access to this information is denied.

See The Java Language Specification, sections 8.2 and 8.4.

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.

The method throws a SecurityException if access to this 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.

The method throws a NoSuchFieldException if a matching field is not found.

The method throws a SecurityException if access to the underlying field is denied.

See The Java Language Specification, sections 8.2 and 8.3.

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.

The method throws a NoSuchMethodException a matching method is not found.

The method throws a SecurityException if access to the underlying method is denied.

See The Java Language Specification, sections 8.2 and 8.4.

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.

The method throws a NoSuchMethodException if a matching constructor is not found.

The method throws a SecurityException if access to the underlying constructor 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.

The method throws a SecurityException if access to this 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.

The method throws a SecurityException if access to this information is denied. See The Java Language Specification, sections 8.2 and 8.3.

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.

The method throws a SecurityException if access to this information is denied.

See The Java Language Specification, section 8.2.

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.

The method throws a SecurityException if access to this information is denied.

See The Java Language Specification, section 8.2.

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.

The method throws a NoSuchFieldException if a field with the specified name is not found.

The method throws a SecurityException if access to this 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.

The method throws a NoSuchMethodException if a matching method is not found.

The method throws a SecurityException if access to the underlying method 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.

The method throws a NoSuchMethodException if a matching constructor is not found.

The method throws a SecurityException if access to the underlying constructor 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 String getResourceAsName(String name)

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