public final class Class extends Object
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());
}
| Modifier and Type | Method and Description |
|---|---|
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.
|
public String toString()
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".public static Class forName(String className) throws ClassNotFoundException
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")
className - the fully qualified name of the desired class.Class object for the class with the
specified name.ClassNotFoundException - if the class could not be found.Error - if the function fails for any other reason.public Object newInstance() throws InstantiationException, IllegalAccessException
new
expression with an empty argument list.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 boolean isInstance(Object obj)
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.
obj - the object to checkobj is an instance of this classpublic boolean isAssignableFrom(Class cls)
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.
cls - the Class object to be checkedboolean value indicating whether objects of the
type cls can be assigned to objects of this classNullPointerException - if the specified Class parameter is
null.public boolean isInterface()
Class object represents an
interface type.true if this object represents an interface;
false otherwise.public boolean isArray()
Class object represents an array class.true if this object represents an array class;
false otherwise.public String getName()
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:
returns "(new Object[3]).getClass().getName()
[Ljava.lang.Object;" and:
returns "(new int[3][4][5][6][7][8][9]).getClass().getName()
[[[[[[[I". The encoding of element type names
is as follows:
The class or interface name classname is given in fully qualified form as shown in the example above.B byte C char D double F float I int J long Lclassname; class or interface S short Z boolean
public InputStream getResourceAsStream(String name)
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/resourceNameRelative format:
resourceNameIn 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.
name - name of the desired resourcejava.io.InputStream object.Copyright © 2013, Oracle and/or its affiliates. All rights reserved.
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