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Class.java
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1998-09-22
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/*
* @(#)Class.java 1.57 98/07/01
*
* Copyright 1995-1998 by Sun Microsystems, Inc.,
* 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
* All rights reserved.
*
* This software is the confidential and proprietary information
* of Sun Microsystems, Inc. ("Confidential Information"). You
* shall not disclose such Confidential Information and shall use
* it only in accordance with the terms of the license agreement
* you entered into with Sun.
*/
package java.lang;
import java.lang.reflect.Member;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.Constructor;
import java.io.InputStream;
/**
* Instances of the class </code>Class</code> 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. Finally, the either primitive Java types
* (boolean, byte, char, short, int, long, float, and double) and
* the keyword void are also represented as Class objects.
* <p>
* There is no public constructor for the class </code>Class</code>.
* </code>Class</code> objects are constructed automatically by the Java
* Virtual Machine as classes are loaded and by calls to the
* <code>defineClass</code> method in the class loader.
* <p>
* The following example uses a Class object to print the Class name
* of an object:
* <p><pre><blockquote>
* void printClassName(Object obj) {
* System.out.println("The class of " + obj +
* " is " + obj.getClass().getName());
* }
* </blockquote></pre>
*
* @author unascribed
* @version 1.57, 07/01/98
* @see java.lang.ClassLoader#defineClass(byte[], int, int)
* @since JDK1.0
*/
public final
class Class implements java.io.Serializable {
/*
* Constructor. Only the Java Virtual Machine creates Class
* objects.
*/
private Class() {}
/**
* Converts the object to a string. The string representation is the
* string <code>"class"</code> or <code>"interface"</code> 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.
*
* @return a string representation of this class object.
* @since JDK1.0
*/
public String toString() {
return (isInterface() ? "interface " : (isPrimitive() ? "" : "class "))
+ getName();
}
/**
* Returns the <code>Class</code> 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.
* <p>
* For example, the following code fragment returns the runtime
* <code>Class</code> descriptor for the class named
* <code>java.lang.Thread</code>:
* <ul><code>
* Class t = Class.forName("java.lang.Thread")
* </code></ul>
*
* @param className the fully qualified name of the desired class.
* @return the <code>Class</code> descriptor for the class with the
* specified name.
* @exception ClassNotFoundException if the class could not be found.
* @since JDK1.0
*/
public static native Class forName(String className)
throws ClassNotFoundException;
/**
* Creates a new instance of a class.
*
* @return a newly allocated instance of the class represented by this
* object. This is done exactly as if by a <code>new</code>
* expression with an empty argument list.
* @exception IllegalAccessException if the class or initializer is
* not accessible.
* @exception 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
*/
public native Object newInstance()
throws InstantiationException, IllegalAccessException;
/**
* This method is the dynamic equivalent of the Java language
* <code>instanceof</code> 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.
*
* <p>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.
*
* @param obj The object to check
* @since JDK1.1
*/
public native boolean isInstance(Object obj);
/**
* 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.
*
* <p>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 <em>The Java Language
* Specification</em>, sections 5.1.1 and 5.1.4 , for details.
*
* @exception NullPointerException if the specified Class parameter is null.
* @since JDK1.1
*/
public native boolean isAssignableFrom(Class cls);
/**
* Determines if the specified Class object represents an interface type.
*
* @return <code>true</code> if this object represents an interface;
* <code>false</code> otherwise.
* @since JDK1.0
*/
public native boolean isInterface();
/**
* If this Class object represents an array type, returns true,
* otherwise returns false.
*
* @since JDK1.1
*/
public native boolean isArray();
/**
* Determines if the specified Class object represents a primitive Java
* type.
*
* <p>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.
*
* <p>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 java.lang.Boolean#TYPE
* @see java.lang.Character#TYPE
* @see java.lang.Byte#TYPE
* @see java.lang.Short#TYPE
* @see java.lang.Integer#TYPE
* @see java.lang.Long#TYPE
* @see java.lang.Float#TYPE
* @see java.lang.Double#TYPE
* @see java.lang.Void#TYPE
* @since JDK1.1
*/
public native boolean isPrimitive();
/**
* Returns the fully-qualified name of the type (class, interface,
* array, or primitive) represented by this Class object, as a String.
*
* @return the fully qualified name of the class or interface
* represented by this object.
* @since JDK1.0
*/
public native String getName();
/**
* Determines the class loader for the class.
*
* @return the class loader that created the class or interface
* represented by this object, or <code>null</code> if the
* class was not created by a class loader.
* @see java.lang.ClassLoader
* @since JDK1.0
*/
public native ClassLoader getClassLoader();
/**
* If this object represents any class other than the class
* </code>Object</code>, then the object that represents the superclass
* of that class is returned.
* <p>
* If this object is the one that represents the class
* </code>Object</code> or this object represents an interface,
* </code>null</code> is returned.
*
* @return the superclass of the class represented by this object.
* @since JDK1.0
*/
public native Class getSuperclass();
/**
* Determines the interfaces implemented by the class or interface
* represented by this object.
* <p>
* 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 </code>implements</code>
* clause of the declaration of the class represented by this object.
* <p>
* 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 </code>extends</code> clause of
* the declaration of the interface represented by this object.
* <p>
* If the class or interface implements no interfaces, the method
* returns an array of length 0.
*
* @return an array of interfaces implemented by this class.
* @since JDK1.0
*/
public native Class[] getInterfaces();
/**
* If this class represents an array type, returns the Class
* object representing the component type of the array; otherwise
* returns null.
*
* @see java.lang.reflect.Array
* @since JDK1.1
*/
public native Class getComponentType();
/**
* 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.
*
* <p>The modifier encodings are defined in <em>The Java Virtual
* Machine Specification</em>, table 4.1.
*
* @see java.lang.reflect.Modifier
* @since JDK1.1
*/
public native int getModifiers();
/**
* Get the signers of this class.
*
* @since JDK1.1
*/
public native Object[] getSigners();
/**
* Set the signers of this class.
*/
native void setSigners(Object[] signers);
/**
* Not implemented in this version of the
* Java<font size="-2"><sup>TM</sup></font> Development Kit.
* <p>
* 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
* <em>declaring class</em>). Returns null if this class or
* interface is not a member of any other class.
*
* @since JDK1.1
*/
public Class getDeclaringClass() {
return null; /* not implemented */
}
/**
* Not implemented in this version of the
* Java<font size="-2"><sup>TM</sup></font> Development Kit.
* <p>
* 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.
*
* @since JDK1.1
*/
public Class[] getClasses() {
return new Class[0]; /* not implemented */
}
/**
* 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.
*
* <p>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.
*
* <p>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.
*
* <p>See <em>The Java Language Specification</em>, sections 8.2 and 8.3.
*
* @exception SecurityException if access to the information is denied.
* @see java.lang.reflect.Field
* @since JDK1.1
*/
public Field[] getFields() throws SecurityException {
checkMemberAccess(Member.PUBLIC);
return getFields0(Member.PUBLIC);
}
/**
* Returns an array containing Method objects reflecting all the
* public <em>member</em> 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.
*
* <p>See <em>The Java Language Specification</em>, sections 8.2
* and 8.4.
*
* @exception SecurityException if access to the information is denied.
* @see java.lang.reflect.Method
* @since JDK1.1
*/
public Method[] getMethods() throws SecurityException {
checkMemberAccess(Member.PUBLIC);
return getMethods0(Member.PUBLIC);
}
/**
* 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.
*
* @exception SecurityException if access to the information is denied.
* @see java.lang.reflect.Constructor
* @since JDK1.1
*/
public Constructor[] getConstructors() throws SecurityException {
checkMemberAccess(Member.PUBLIC);
return getConstructors0(Member.PUBLIC);
}
/**
* 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.
*
* <p>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.
*
* <p>See <em>The Java Language Specification</em>, sections 8.2 and 8.3.
*
* @exception NoSuchFieldException if a field with the specified name is
* not found.
* @exception SecurityException if access to the information is denied.
* @see java.lang.reflect.Field
* @since JDK1.1
*/
public Field getField(String name)
throws NoSuchFieldException, SecurityException {
checkMemberAccess(Member.PUBLIC);
return getField0(name, Member.PUBLIC);
}
/**
* 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.
*
* <p>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.
*
* <p>See <em>The Java Language Specification</em>, sections 8.2
* and 8.4.
*
* @exception NoSuchMethodException if a matching method is not found.
* @exception SecurityException if access to the information is denied.
* @see java.lang.reflect.Method
* @since JDK1.1
*/
public Method getMethod(String name, Class[] parameterTypes)
throws NoSuchMethodException, SecurityException {
checkMemberAccess(Member.PUBLIC);
return getMethod0(name, parameterTypes, Member.PUBLIC);
}
/**
* 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.
*
* <p>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.
*
* @exception NoSuchMethodException if a matching method is not found.
* @exception SecurityException if access to the information is denied.
* @see java.lang.reflect.Constructor
* @since JDK1.1
*/
public Constructor getConstructor(Class[] parameterTypes)
throws NoSuchMethodException, SecurityException {
checkMemberAccess(Member.PUBLIC);
return getConstructor0(parameterTypes, Member.PUBLIC);
}
/**
* Not implemented in this version of the
* Java<font size="-2"><sup>TM</sup></font> Development Kit.
* <p>
* 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.
*
* @exception SecurityException if access to the information is denied.
* @since JDK1.1
*/
public Class[] getDeclaredClasses() throws SecurityException {
checkMemberAccess(Member.DECLARED);
return new Class[0]; /* not implemented */
}
/**
* 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 <em>The Java Language Specification</em>, sections 8.2 and
* 8.3.
*
* @exception SecurityException if access to the information is denied.
* @see java.lang.reflect.Field
* @since JDK1.1
*/
public Field[] getDeclaredFields() throws SecurityException {
checkMemberAccess(Member.DECLARED);
return getFields0(Member.DECLARED);
}
/**
* 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.
*
* <p>See <em>The Java Language Specification</em>, section 8.2.
*
* @exception SecurityException if access to the information is denied.
* @see java.lang.reflect.Method
* @since JDK1.1
*/
public Method[] getDeclaredMethods() throws SecurityException {
checkMemberAccess(Member.DECLARED);
return getMethods0(Member.DECLARED);
}
/**
* 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.
*
* <p>See <em>The Java Language Specification</em>, section 8.2.
*
* @exception SecurityException if access to the information is denied.
* @see java.lang.reflect.Constructor
* @since JDK1.1
*/
public Constructor[] getDeclaredConstructors() throws SecurityException {
checkMemberAccess(Member.DECLARED);
return getConstructors0(Member.DECLARED);
}
/**
* 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.
*
* @exception NoSuchFieldException if a field with the specified name is
* not found.
* @exception SecurityException if access to the information is denied.
* @see java.lang.reflect.Field
* @since JDK1.1
*/
public Field getDeclaredField(String name)
throws NoSuchFieldException, SecurityException {
checkMemberAccess(Member.DECLARED);
return getField0(name, Member.DECLARED);
}
/**
* 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.
*
* @exception NoSuchMethodException if a matching method is not found.
* @exception SecurityException if access to the information is denied.
* @see java.lang.reflect.Method
* @since JDK1.1
*/
public Method getDeclaredMethod(String name, Class[] parameterTypes)
throws NoSuchMethodException, SecurityException {
checkMemberAccess(Member.DECLARED);
return getMethod0(name, parameterTypes, Member.DECLARED);
}
/**
* 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.
*
* @exception NoSuchMethodException if a matching method is not found.
* @exception SecurityException if access to the information is denied.
* @see java.lang.reflect.Constructor
* @since JDK1.1
*/
public Constructor getDeclaredConstructor(Class[] parameterTypes)
throws NoSuchMethodException, SecurityException {
checkMemberAccess(Member.DECLARED);
return getConstructor0(parameterTypes, Member.DECLARED);
}
/**
* Finds 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.<p>
*
* 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 "/".
*
* @param name the string representing the resource to be found
* @return the <code>InputStream</code> object having the
* specified name, or <code>null</code> if no
* resource with the specified name is found.
* @see java.lang.ClassLoader
* @see java.lang.Class#getResource
* @since JDK1.1
*/
public InputStream getResourceAsStream(String name) {
name = resolveName(name);
ClassLoader cl = getClassLoader();
if (cl==null) {
// A system class.
return ClassLoader.getSystemResourceAsStream(name);
}
return cl.getResourceAsStream(name);
}
/**
* Finds a resource with the specified name. The rules for searching
* for resources associated with a given class are implemented by
* the class loader of the class.
* <p>
* 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 "/".
*
* @param name the string representing the resource to be found.
* @return the <code>URL</code> object having the specified name,
* or <code>null</code> if no resource with the specified
* name is found.
* @see java.lang.ClassLoader
* @see java.lang.Class#getResourceAsStream
* @since JDK1.1
*/
public java.net.URL getResource(String name) {
name = resolveName(name);
ClassLoader cl = getClassLoader();
if (cl==null) {
// A system class.
return ClassLoader.getSystemResource(name);
}
return cl.getResource(name);
}
/*
* Return the Virtual Machine's Class object for the named
* primitive type.
*/
static native Class getPrimitiveClass(String name);
/*
* Check if client is allowed to access members. If access is
* denied, throw a SecurityException.
*
* <p>Default policy: allow all clients access with normal Java
* access control.
*/
private void checkMemberAccess(int which) {
SecurityManager s = System.getSecurityManager();
if (s != null) {
s.checkMemberAccess(this, which);
}
}
/**
* Add a package name prefix if the name is not absolute
* Remove leading "/" if name is absolute
*/
private String resolveName(String name) {
if (name == null) {
return name;
}
if (!name.startsWith("/")) {
Class c = this;
while (c.isArray()) {
c = c.getComponentType();
}
String baseName = c.getName();
int index = baseName.lastIndexOf('.');
if (index != -1) {
name = baseName.substring(0, index).replace('.', '/')
+"/"+name;
}
} else {
name = name.substring(1);
}
return name;
}
private native Field[] getFields0(int which);
private native Method[] getMethods0(int which);
private native Constructor[] getConstructors0(int which);
private native Field getField0(String name, int which);
private native Method getMethod0(String name, Class[] parameterTypes,
int which);
private native Constructor getConstructor0(Class[] parameterTypes,
int which);
}