java.lang
Class Class

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

public final class Class

extends Object

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());
     }
 

Since:

JDK1.0, CLDC 1.0

Method Summary

static Class	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 in the application's JAR file.
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.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Method Detail

toString

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".

Overrides:

toString in class Object

Returns:

a string representation of this class object.

forName

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, this method attempts to locate, load and link the class.

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 object for the class with the specified name.

Throws:

ClassNotFoundException - if the class could not be found.

Error - if the function fails for any other reason.

Since:

JDK1.0

newInstance

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.

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

Since:

JDK1.0

isInstance

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

Since:

JDK1.1

isAssignableFrom

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.

Since:

JDK1.1

isInterface

public boolean isInterface()

Determines if the specified Class object represents an interface type.

Returns:

true if this object represents an interface; false otherwise.

isArray

public boolean isArray()

Determines if this Class object represents an array class.

Returns:

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

Since:

JDK1.1

getName

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.

getResourceAsStream

public InputStream getResourceAsStream(String name)

Finds a resource with a given name in the application's JAR file. This method returns null if no resource with this name is found in the application's JAR file.

The resource names can be represented in two different formats: absolute or relative.

Absolute format:

/packagePathName/resourceName

Relative format:

resourceName

In the absolute format, the programmer provides a fully qualified name that includes both the full path and the name of the resource inside the JAR file. In the path names, the character "/" is used as the separator.

In the relative format, the programmer provides only the name of the actual resource. Relative names are converted to absolute names by the system by prepending the resource name with the fully qualified package name of class upon which the getResourceAsStream method was called.

Parameters:

name - name of the desired resource

Returns:

a java.io.InputStream object.