java.lang.reflect

Class Method

java.lang.Object

java.lang.reflect.AccessibleObject

java.lang.reflect.Method

All Implemented Interfaces:

AnnotatedElement, GenericDeclaration, Member

public final class Method
extends AccessibleObject
implements Member, GenericDeclaration

The Method class represents a member method of a class. It also allows dynamic invocation, via reflection. This works for both static and instance methods. Invocation on Method objects knows how to do widening conversions, but throws IllegalArgumentException if a narrowing conversion would be necessary. You can query for information on this Method regardless of location, but invocation access may be limited by Java language access controls. If you can't do it in the compiler, you can't normally do it here either.

Note: This class returns and accepts types as Classes, even primitive types; there are Class types defined that represent each different primitive type. They are java.lang.Boolean.TYPE, java.lang.Byte.TYPE,, also available as boolean.class, byte.class, etc. These are not to be confused with the classes java.lang.Boolean, java.lang.Byte, etc., which are real classes.

Also note that this is not a serializable class. It is entirely feasible to make it serializable using the Externalizable interface, but this is on Sun, not me.

Since:

1.1

See Also:

Member, Class, Class.getMethod(String,Class[]), Class.getDeclaredMethod(String,Class[]), Class.getMethods(), Class.getDeclaredMethods()

Field Summary

Fields inherited from interface java.lang.reflect.Member

DECLARED, PUBLIC

Method Summary

Methods

Modifier and Type	Method and Description
boolean	equals(java.lang.Object o) Compare two objects to see if they are semantically equivalent.
<T extends java.lang.annotation.Annotation> T	getAnnotation(java.lang.Class<T> annotationClass) Returns the element's annotation for the specified annotation type, or null if no such annotation exists.
java.lang.annotation.Annotation[]	getDeclaredAnnotations() Returns all annotations directly defined by the element.
java.lang.Class<?>	getDeclaringClass() Gets the class that declared this method, or the class where this method is a non-inherited member.
java.lang.Object	getDefaultValue() If this method is an annotation method, returns the default value for the method.
java.lang.Class<?>[]	getExceptionTypes() Get the exception types this method says it throws, in no particular order.
Type[]	getGenericExceptionTypes() Returns an array of Type objects that represents the exception types declared by this method, in declaration order.
Type[]	getGenericParameterTypes() Returns an array of Type objects that represents the parameter list for this method, in declaration order.
Type	getGenericReturnType() Returns the return type of this method.
int	getModifiers() Gets the modifiers this method uses.
java.lang.String	getName() Gets the name of this method.
java.lang.annotation.Annotation[][]	getParameterAnnotations() Return an array of arrays representing the annotations on each of the method's parameters.
java.lang.Class<?>[]	getParameterTypes() Get the parameter list for this method, in declaration order.
java.lang.Class<?>	getReturnType() Gets the return type of this method.
TypeVariable<Method>[]	getTypeParameters() Returns an array of TypeVariable objects that represents the type variables declared by this constructor, in declaration order.
int	hashCode() Get the hash code for the Method.
java.lang.Object	invoke(java.lang.Object o, java.lang.Object... args) Invoke the method.
boolean	isBridge() Return true if this method is a bridge method.
boolean	isSynthetic() Return true if this method is synthetic, false otherwise.
boolean	isVarArgs() Return true if this is a varargs method, that is if the method takes a variable number of arguments.
java.lang.String	toGenericString()
java.lang.String	toString() Get a String representation of the Method.

Methods inherited from class java.lang.reflect.AccessibleObject

getAnnotations, isAccessible, isAnnotationPresent, setAccessible, setAccessible

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Method Detail

getDeclaringClass

public java.lang.Class<?> getDeclaringClass()

Gets the class that declared this method, or the class where this method is a non-inherited member.

Specified by:

getDeclaringClass in interface Member

Returns:

the class that declared this member

getName

public java.lang.String getName()

Gets the name of this method.

Specified by:

getName in interface Member

Returns:

the name of this method

getModifiers

public int getModifiers()

Gets the modifiers this method uses. Use the Modifier class to interpret the values. A method can only have a subset of the following modifiers: public, private, protected, abstract, static, final, synchronized, native, and strictfp.

Specified by:

getModifiers in interface Member

Returns:

an integer representing the modifiers to this Member

See Also:

Modifier

isBridge

public boolean isBridge()

Return true if this method is a bridge method. A bridge method is generated by the compiler in some situations involving generics and inheritance.

Since:

1.5

isSynthetic

public boolean isSynthetic()

Return true if this method is synthetic, false otherwise.

Specified by:

isSynthetic in interface Member

Returns:

true if the member is synthetic

Since:

1.5

isVarArgs

public boolean isVarArgs()

Return true if this is a varargs method, that is if the method takes a variable number of arguments.

Since:

1.5

getReturnType

public java.lang.Class<?> getReturnType()

Gets the return type of this method.

Returns:

the type of this method

getParameterTypes

public java.lang.Class<?>[] getParameterTypes()

Get the parameter list for this method, in declaration order. If the method takes no parameters, returns a 0-length array (not null).

Returns:

a list of the types of the method's parameters

getExceptionTypes

public java.lang.Class<?>[] getExceptionTypes()

Get the exception types this method says it throws, in no particular order. If the method has no throws clause, returns a 0-length array (not null).

Returns:

a list of the types in the method's throws clause

equals

public boolean equals(java.lang.Object o)

Compare two objects to see if they are semantically equivalent. Two Methods are semantically equivalent if they have the same declaring class, name, parameter list, and return type.

Overrides:

equals in class java.lang.Object

Parameters:

o - the object to compare to

Returns:

true if they are equal; false if not

See Also:

Object.hashCode()

hashCode

public int hashCode()

Get the hash code for the Method. The Method hash code is the hash code of its name XOR'd with the hash code of its class name.

Overrides:

hashCode in class java.lang.Object

Returns:

the hash code for the object

See Also:

Object.equals(Object), System.identityHashCode(Object)

toString

public java.lang.String toString()

Get a String representation of the Method. A Method's String representation is "<modifiers> <returntype> <methodname>(<paramtypes>) throws <exceptions>", where everything after ')' is omitted if there are no exceptions.
Example: public static int run(java.lang.Runnable,int)

Overrides:

toString in class java.lang.Object

Returns:

the String representation of the Method

See Also:

Object.getClass(), Object.hashCode(), Class.getName(), Integer.toHexString(int)

toGenericString

public java.lang.String toGenericString()

invoke

public java.lang.Object invoke(java.lang.Object o,
                      java.lang.Object... args)
                        throws java.lang.IllegalAccessException,
                               InvocationTargetException

Invoke the method. Arguments are automatically unwrapped and widened, and the result is automatically wrapped, if needed.

If the method is static, o will be ignored. Otherwise, the method uses dynamic lookup as described in JLS 15.12.4.4. You cannot mimic the behavior of nonvirtual lookup (as in super.foo()). This means you will get a NullPointerException if o is null, and an IllegalArgumentException if it is incompatible with the declaring class of the method. If the method takes 0 arguments, you may use null or a 0-length array for args.

Next, if this Method enforces access control, your runtime context is evaluated, and you may have an IllegalAccessException if you could not acces this method in similar compiled code. If the method is static, and its class is uninitialized, you trigger class initialization, which may end in a ExceptionInInitializerError.

Finally, the method is invoked. If it completes normally, the return value will be null for a void method, a wrapped object for a primitive return method, or the actual return of an Object method. If it completes abruptly, the exception is wrapped in an InvocationTargetException.

Parameters:

o - the object to invoke the method on

args - the arguments to the method

Returns:

the return value of the method, wrapped in the appropriate wrapper if it is primitive

Throws:

java.lang.IllegalAccessException - if the method could not normally be called by the Java code (i.e. it is not public)

java.lang.IllegalArgumentException - if the number of arguments is incorrect; if the arguments types are wrong even with a widening conversion; or if o is not an instance of the class or interface declaring this method

InvocationTargetException - if the method throws an exception

java.lang.NullPointerException - if o is null and this field requires an instance

java.lang.ExceptionInInitializerError - if accessing a static method triggered class initialization, which then failed

getTypeParameters

public TypeVariable<Method>[] getTypeParameters()

Returns an array of TypeVariable objects that represents the type variables declared by this constructor, in declaration order. An array of size zero is returned if this class has no type variables.

Specified by:

getTypeParameters in interface GenericDeclaration

Returns:

the type variables associated with this class.

Throws:

GenericSignatureFormatError - if the generic signature does not conform to the format specified in the Virtual Machine specification, version 3.

Since:

1.5

getGenericExceptionTypes

public Type[] getGenericExceptionTypes()

Returns an array of Type objects that represents the exception types declared by this method, in declaration order. An array of size zero is returned if this method declares no exceptions.

Returns:

the exception types declared by this method.

Throws:

GenericSignatureFormatError - if the generic signature does not conform to the format specified in the Virtual Machine specification, version 3.

Since:

1.5

getGenericParameterTypes

public Type[] getGenericParameterTypes()

Returns an array of Type objects that represents the parameter list for this method, in declaration order. An array of size zero is returned if this method takes no parameters.

Returns:

a list of the types of the method's parameters

Throws:

GenericSignatureFormatError - if the generic signature does not conform to the format specified in the Virtual Machine specification, version 3.

Since:

1.5

getGenericReturnType

public Type getGenericReturnType()

Returns the return type of this method.

Returns:

the return type of this method

Throws:

GenericSignatureFormatError - if the generic signature does not conform to the format specified in the Virtual Machine specification, version 3.

Since:

1.5

getDefaultValue

public java.lang.Object getDefaultValue()

If this method is an annotation method, returns the default value for the method. If there is no default value, or if the method is not a member of an annotation type, returns null. Primitive types are wrapped.

Throws:

java.lang.TypeNotPresentException - if the method returns a Class, and the class cannot be found

Since:

1.5

getParameterAnnotations

public java.lang.annotation.Annotation[][] getParameterAnnotations()

Return an array of arrays representing the annotations on each of the method's parameters. The outer array is aligned against the parameters of the method and is thus equal in length to the number of parameters (thus having a length zero if there are none). Each array element in the outer array contains an inner array which holds the annotations. This array has a length of zero if the parameter has no annotations.

The returned annotations are serialized. Changing the annotations has no affect on the return value of future calls to this method.

Returns:

an array of arrays which represents the annotations used on the parameters of this method. The order of the array elements matches the declaration order of the parameters.

Since:

1.5

getAnnotation

public <T extends java.lang.annotation.Annotation> T getAnnotation(java.lang.Class<T> annotationClass)

Returns the element's annotation for the specified annotation type, or null if no such annotation exists.

Specified by:

getAnnotation in interface AnnotatedElement

Overrides:

getAnnotation in class AccessibleObject

Parameters:

annotationClass - the type of annotation to look for.

Returns:

this element's annotation for the specified type, or null if no such annotation exists.

Throws:

java.lang.NullPointerException - if the annotation class is null.

getDeclaredAnnotations

public java.lang.annotation.Annotation[] getDeclaredAnnotations()

Returns all annotations directly defined by the element. If there are no annotations directly associated with the element, then a zero-length array will be returned. The returned array may be modified by the client code, but this will have no effect on the annotation content of this class, and hence no effect on the return value of this method for future callers.

Specified by:

getDeclaredAnnotations in interface AnnotatedElement

Overrides:

getDeclaredAnnotations in class AccessibleObject

Returns:

the annotations directly defined by the element.

Since:

1.5