public final class

Class

extends Object
java.lang.Object
   ↳ java.lang.Class<T>

Class Overview

Instances of the class Class represent classes and interfaces in a running Java application. Every array also belongs to a class that is reflected as a Class object that is shared by all arrays with the same element type and number of dimensions.

Class has no public constructor. Instead Class objects are constructed automatically by the Java Virtual Machine as classes are loaded.

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());
 }

Summary

Public Methods
static <E> Class<E> forName(String className)
Returns the Class object associated with the class with the given string name.
String getName()
Returns the fully-qualified name of the entity (class, interface, array class, primitive type, or void) represented by this Class object, as a String.
InputStream getResourceAsStream(String name)
Finds a resource with a given name.
Class<? super T> getSuperclass()
Returns the Class representing the superclass of the entity (class, interface, primitive type or void) represented by this Class.
boolean isArray()
Determines if this Class object represents an array class.
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.
boolean isInstance(Object obj)
Determines if the specified Object is assignment-compatible with the object represented by this Class.
boolean isInterface()
Determines if the specified Class object represents an interface type.
Object newInstance()
Creates a new instance of a class.
String toString()
Converts the object to a string.
[Expand]
Inherited Methods
From class java.lang.Object

Public Methods

public static Class<E> forName (String className)

Returns the Class object associated with the class with the given string name. 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 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 String getName ()

Returns the fully-qualified name of the entity (class, interface, array class, primitive type, or void) 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 InputStream getResourceAsStream (String name)

Finds a resource with a given name. This method returns null if no resource with this name is found. The rules for searching resources associated with a given class are profile specific.

Parameters
name name of the desired resource
Returns
  • a java.io.InputStream object.
See Also

public Class<? super T> getSuperclass ()

Returns the Class representing the superclass of the entity (class, interface, primitive type or void) represented by this Class. If this Class represents either the Object class, an interface, a primitive type, or void, then null is returned. If this object represents an array class then the Class object representing the Object class is returned.

Returns
  • the superclass of the class represented by this object.

public boolean isArray ()

Determines if this Class object represents an array class.

Returns
  • true if this object represents an array class; false otherwise.

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; otherwise it returns false. If this Class object represents a primitive type, this method returns true if the specified Class parameter is exactly this Class object; otherwise it returns false.

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.

Parameters
cls the Class object to be checked
Returns
  • the boolean value indicating whether objects of the type cls can be assigned to objects of this class
Throws
NullPointerException if the specified Class parameter is null.

public boolean isInstance (Object obj)

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

Parameters
obj the object to check
Returns
  • true if obj is an instance of this class

public boolean isInterface ()

Determines if the specified Class object represents an interface type.

Returns
  • true if this object represents an interface; false otherwise.

public Object newInstance ()

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

public String toString ()

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

Returns
  • a string representation of this class object.