java.lang.reflect

Class Method

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 (String,Class[]) (String,Class[]) getMethods getDeclaredMethods

UNKNOWN: updated to 1.4

Method Summary
booleanequals(Object obj)
Compare two objects to see if they are semantically equivalent.
<T extends Annotation> TgetAnnotation(Class<T> annoClass)
Annotation[]getDeclaredAnnotations()
Class<?>getDeclaringClass()
Gets the class that declared this method, or the class where this method is a non-inherited member.
ObjectgetDefaultValue()
If this method is an annotation method, returns the default value for the method.
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.
TypegetGenericReturnType()
Returns the return type of this method.
intgetModifiers()
Gets the modifiers this method uses.
StringgetName()
Gets the name of this method.
Annotation[][]getParameterAnnotations()
Class<?>[]getParameterTypes()
Get the parameter list for this method, in declaration order.
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.
inthashCode()
Get the hash code for the Method.
Objectinvoke(Object obj, Object... args)
Invoke the method.
booleanisBridge()
Return true if this method is a bridge method.
booleanisSynthetic()
Return true if this method is synthetic, false otherwise.
booleanisVarArgs()
Return true if this is a varargs method, that is if the method takes a variable number of arguments.
StringtoGenericString()
StringtoString()
Get a String representation of the Method.

Method Detail

equals

public boolean equals(Object obj)
Compare two objects to see if they are semantically equivalent. Two Methods are semantically equivalent if they have the same declaring class, name, and parameter list. This ignores different exception clauses or return types.

Parameters: o the object to compare to

Returns: true if they are equal; false if not

getAnnotation

public <T extends Annotation> T getAnnotation(Class<T> annoClass)

getDeclaredAnnotations

public Annotation[] getDeclaredAnnotations()

getDeclaringClass

public Class<?> getDeclaringClass()
Gets the class that declared this method, or the class where this method is a non-inherited member.

Returns: the class that declared this member

getDefaultValue

public 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: TypeNotPresentException if the method returns a Class, and the class cannot be found

Since: 1.5

getExceptionTypes

public 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

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

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.

Returns: an integer representing the modifiers to this Member

See Also: Modifier

getName

public String getName()
Gets the name of this method.

Returns: the name of this method

getParameterAnnotations

public Annotation[][] getParameterAnnotations()

getParameterTypes

public 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

getReturnType

public Class<?> getReturnType()
Gets the return type of this method.

Returns: the type of this method

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.

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

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.

Returns: the hash code for the object

invoke

public Object invoke(Object obj, Object... args)
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: IllegalAccessException if the method could not normally be called by the Java code (i.e. it is not public) 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 NullPointerException if o is null and this field requires an instance ExceptionInInitializerError if accessing a static method triggered class initialization, which then failed

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.

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

toGenericString

public String toGenericString()

toString

public 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)

Returns: the String representation of the Method