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public
final
class
MethodType
extends Object
implements
Serializable
java.lang.Object | |
↳ | java.lang.invoke.MethodType |
A method type represents the arguments and return type accepted and
returned by a method handle, or the arguments and return type passed
and expected by a method handle caller. Method types must be properly
matched between a method handle and all its callers,
and the JVM's operations enforce this matching at, specifically
during calls to MethodHandle#invokeExact
and MethodHandle#invoke
, and during execution
of invokedynamic
instructions.
The structure is a return type accompanied by any number of parameter types.
The types (primitive, void
, and reference) are represented by Class
objects.
(For ease of exposition, we treat void
as if it were a type.
In fact, it denotes the absence of a return type.)
All instances of MethodType
are immutable.
Two instances are completely interchangeable if they compare equal.
Equality depends on pairwise correspondence of the return and parameter types and on nothing else.
This type can be created only by factory methods. All factory methods may cache values, though caching is not guaranteed. Some factory methods are static, while others are virtual methods which modify precursor method types, e.g., by changing a selected parameter.
Factory methods which operate on groups of parameter types
are systematically presented in two versions, so that both Java arrays and
Java lists can be used to work with groups of parameter types.
The query methods parameterArray
and parameterList
also provide a choice between arrays and lists.
MethodType
objects are sometimes derived from bytecode instructions
such as invokedynamic
, specifically from the type descriptor strings associated
with the instructions in a class file's constant pool.
Like classes and strings, method types can also be represented directly
in a class file's constant pool as constants.
A method type may be loaded by an ldc
instruction which refers
to a suitable CONSTANT_MethodType
constant pool entry.
The entry refers to a CONSTANT_Utf8
spelling for the descriptor string.
(For full details on method type constants,
see sections 4.4.8 and 5.4.3.5 of the Java Virtual Machine Specification.)
When the JVM materializes a MethodType
from a descriptor string,
all classes named in the descriptor must be accessible, and will be loaded.
(But the classes need not be initialized, as is the case with a CONSTANT_Class
.)
This loading may occur at any time before the MethodType
object is first derived.
Public methods | |
---|---|
MethodType
|
appendParameterTypes(Class...<?> ptypesToInsert)
Finds or creates a method type with additional parameter types. |
MethodType
|
appendParameterTypes(List<Class<?>> ptypesToInsert)
Finds or creates a method type with additional parameter types. |
MethodType
|
changeParameterType(int num, Class<?> nptype)
Finds or creates a method type with a single different parameter type. |
MethodType
|
changeReturnType(Class<?> nrtype)
Finds or creates a method type with a different return type. |
MethodType
|
dropParameterTypes(int start, int end)
Finds or creates a method type with some parameter types omitted. |
boolean
|
equals(Object x)
Compares the specified object with this type for equality. |
MethodType
|
erase()
Erases all reference types to |
static
MethodType
|
fromMethodDescriptorString(String descriptor, ClassLoader loader)
Finds or creates an instance of a method type, given the spelling of its bytecode descriptor. |
MethodType
|
generic()
Converts all types, both reference and primitive, to |
static
MethodType
|
genericMethodType(int objectArgCount, boolean finalArray)
Finds or creates a method type whose components are |
static
MethodType
|
genericMethodType(int objectArgCount)
Finds or creates a method type whose components are all |
boolean
|
hasPrimitives()
Reports if this type contains a primitive argument or return value. |
boolean
|
hasWrappers()
Reports if this type contains a wrapper argument or return value. |
int
|
hashCode()
Returns the hash code value for this method type. |
MethodType
|
insertParameterTypes(int num, Class...<?> ptypesToInsert)
Finds or creates a method type with additional parameter types. |
MethodType
|
insertParameterTypes(int num, List<Class<?>> ptypesToInsert)
Finds or creates a method type with additional parameter types. |
static
MethodType
|
methodType(Class<?> rtype, MethodType ptypes)
Finds or creates a method type with the given components. |
static
MethodType
|
methodType(Class<?> rtype, Class[]<?> ptypes)
Finds or creates an instance of the given method type. |
static
MethodType
|
methodType(Class<?> rtype, Class<?> ptype0)
Finds or creates a method type with the given components. |
static
MethodType
|
methodType(Class<?> rtype)
Finds or creates a method type with the given components. |
static
MethodType
|
methodType(Class<?> rtype, List<Class<?>> ptypes)
Finds or creates a method type with the given components. |
static
MethodType
|
methodType(Class<?> rtype, Class<?> ptype0, Class...<?> ptypes)
Finds or creates a method type with the given components. |
Class[]<?>
|
parameterArray()
Presents the parameter types as an array (a convenience method). |
int
|
parameterCount()
Returns the number of parameter types in this method type. |
List<Class<?>>
|
parameterList()
Presents the parameter types as a list (a convenience method). |
Class<?>
|
parameterType(int num)
Returns the parameter type at the specified index, within this method type. |
Class<?>
|
returnType()
Returns the return type of this method type. |
String
|
toMethodDescriptorString()
Produces a bytecode descriptor representation of the method type. |
String
|
toString()
Returns a string representation of the method type,
of the form |
MethodType
|
unwrap()
Converts all wrapper types to their corresponding primitive types. |
MethodType
|
wrap()
Converts all primitive types to their corresponding wrapper types. |
Inherited methods | |
---|---|
public MethodType appendParameterTypes (Class...<?> ptypesToInsert)
Finds or creates a method type with additional parameter types.
Convenience method for methodType
.
Parameters | |
---|---|
ptypesToInsert |
Class : zero or more new parameter types to insert after the end of the parameter list |
Returns | |
---|---|
MethodType |
the same type, except with the selected parameter(s) appended |
Throws | |
---|---|
IllegalArgumentException |
if any element of ptypesToInsert is void.class
or if the resulting method type would have more than 255 parameter slots |
NullPointerException |
if ptypesToInsert or any of its elements is null |
public MethodType appendParameterTypes (List<Class<?>> ptypesToInsert)
Finds or creates a method type with additional parameter types.
Convenience method for methodType
.
Parameters | |
---|---|
ptypesToInsert |
List : zero or more new parameter types to insert after the end of the parameter list |
Returns | |
---|---|
MethodType |
the same type, except with the selected parameter(s) appended |
Throws | |
---|---|
IllegalArgumentException |
if any element of ptypesToInsert is void.class
or if the resulting method type would have more than 255 parameter slots |
NullPointerException |
if ptypesToInsert or any of its elements is null |
public MethodType changeParameterType (int num, Class<?> nptype)
Finds or creates a method type with a single different parameter type.
Convenience method for methodType
.
Parameters | |
---|---|
num |
int : the index (zero-based) of the parameter type to change |
nptype |
Class : a new parameter type to replace the old one with |
Returns | |
---|---|
MethodType |
the same type, except with the selected parameter changed |
Throws | |
---|---|
IndexOutOfBoundsException |
if num is not a valid index into parameterArray() |
IllegalArgumentException |
if nptype is void.class |
NullPointerException |
if nptype is null |
public MethodType changeReturnType (Class<?> nrtype)
Finds or creates a method type with a different return type.
Convenience method for methodType
.
Parameters | |
---|---|
nrtype |
Class : a return parameter type to replace the old one with |
Returns | |
---|---|
MethodType |
the same type, except with the return type change |
Throws | |
---|---|
NullPointerException |
if nrtype is null |
public MethodType dropParameterTypes (int start, int end)
Finds or creates a method type with some parameter types omitted.
Convenience method for methodType
.
Parameters | |
---|---|
start |
int : the index (zero-based) of the first parameter type to remove |
end |
int : the index (greater than start ) of the first parameter type after not to remove |
Returns | |
---|---|
MethodType |
the same type, except with the selected parameter(s) removed |
Throws | |
---|---|
IndexOutOfBoundsException |
if start is negative or greater than parameterCount()
or if end is negative or greater than parameterCount()
or if start is greater than end |
public boolean equals (Object x)
Compares the specified object with this type for equality. That is, it returns true if and only if the specified object is also a method type with exactly the same parameters and return type.
Parameters | |
---|---|
x |
Object : object to compare |
Returns | |
---|---|
boolean |
true if this object is the same as the obj
argument; false otherwise. |
See also:
public MethodType erase ()
Erases all reference types to Object
.
Convenience method for methodType
.
All primitive types (including void
) will remain unchanged.
Returns | |
---|---|
MethodType |
a version of the original type with all reference types replaced |
public static MethodType fromMethodDescriptorString (String descriptor, ClassLoader loader)
Finds or creates an instance of a method type, given the spelling of its bytecode descriptor.
Convenience method for methodType
.
Any class or interface name embedded in the descriptor string
will be resolved by calling ClassLoader#loadClass(java.lang.String)
on the given loader (or if it is null, on the system class loader).
Note that it is possible to encounter method types which cannot be constructed by this method, because their component types are not all reachable from a common class loader.
This method is included for the benefit of applications that must
generate bytecodes that process method handles and invokedynamic
.
Parameters | |
---|---|
descriptor |
String : a bytecode-level type descriptor string "(T...)T" |
loader |
ClassLoader : the class loader in which to look up the types |
Returns | |
---|---|
MethodType |
a method type matching the bytecode-level type descriptor |
Throws | |
---|---|
NullPointerException |
if the string is null |
IllegalArgumentException |
if the string is not well-formed |
TypeNotPresentException |
if a named type cannot be found |
public MethodType generic ()
Converts all types, both reference and primitive, to Object
.
Convenience method for genericMethodType
.
The expression type.wrap().erase()
produces the same value
as type.generic()
.
Returns | |
---|---|
MethodType |
a version of the original type with all types replaced |
public static MethodType genericMethodType (int objectArgCount, boolean finalArray)
Finds or creates a method type whose components are Object
with an optional trailing Object[]
array.
Convenience method for methodType
.
All parameters and the return type will be Object
,
except the final array parameter if any, which will be Object[]
.
Parameters | |
---|---|
objectArgCount |
int : number of parameters (excluding the final array parameter if any) |
finalArray |
boolean : whether there will be a trailing array parameter, of type Object[] |
Returns | |
---|---|
MethodType |
a generally applicable method type, for all calls of the given fixed argument count and a collected array of further arguments |
Throws | |
---|---|
IllegalArgumentException |
if objectArgCount is negative or greater than 255 (or 254, if finalArray is true) |
See also:
public static MethodType genericMethodType (int objectArgCount)
Finds or creates a method type whose components are all Object
.
Convenience method for methodType
.
All parameters and the return type will be Object.
Parameters | |
---|---|
objectArgCount |
int : number of parameters |
Returns | |
---|---|
MethodType |
a generally applicable method type, for all calls of the given argument count |
Throws | |
---|---|
IllegalArgumentException |
if objectArgCount is negative or greater than 255 |
See also:
public boolean hasPrimitives ()
Reports if this type contains a primitive argument or return value.
The return type void
counts as a primitive.
Returns | |
---|---|
boolean |
true if any of the types are primitives |
public boolean hasWrappers ()
Reports if this type contains a wrapper argument or return value.
Wrappers are types which box primitive values, such as Integer
.
The reference type java.lang.Void
counts as a wrapper,
if it occurs as a return type.
Returns | |
---|---|
boolean |
true if any of the types are wrappers |
public int hashCode ()
Returns the hash code value for this method type. It is defined to be the same as the hashcode of a List whose elements are the return type followed by the parameter types.
Returns | |
---|---|
int |
the hash code value for this method type |
public MethodType insertParameterTypes (int num, Class...<?> ptypesToInsert)
Finds or creates a method type with additional parameter types.
Convenience method for methodType
.
Parameters | |
---|---|
num |
int : the position (zero-based) of the inserted parameter type(s) |
ptypesToInsert |
Class : zero or more new parameter types to insert into the parameter list |
Returns | |
---|---|
MethodType |
the same type, except with the selected parameter(s) inserted |
Throws | |
---|---|
IndexOutOfBoundsException |
if num is negative or greater than parameterCount() |
IllegalArgumentException |
if any element of ptypesToInsert is void.class
or if the resulting method type would have more than 255 parameter slots |
NullPointerException |
if ptypesToInsert or any of its elements is null |
public MethodType insertParameterTypes (int num, List<Class<?>> ptypesToInsert)
Finds or creates a method type with additional parameter types.
Convenience method for methodType
.
Parameters | |
---|---|
num |
int : the position (zero-based) of the inserted parameter type(s) |
ptypesToInsert |
List : zero or more new parameter types to insert into the parameter list |
Returns | |
---|---|
MethodType |
the same type, except with the selected parameter(s) inserted |
Throws | |
---|---|
IndexOutOfBoundsException |
if num is negative or greater than parameterCount() |
IllegalArgumentException |
if any element of ptypesToInsert is void.class
or if the resulting method type would have more than 255 parameter slots |
NullPointerException |
if ptypesToInsert or any of its elements is null |
public static MethodType methodType (Class<?> rtype, MethodType ptypes)
Finds or creates a method type with the given components.
Convenience method for methodType
.
The resulting method has the same parameter types as ptypes
,
and the specified return type.
Parameters | |
---|---|
rtype |
Class : the return type |
ptypes |
MethodType : the method type which supplies the parameter types |
Returns | |
---|---|
MethodType |
a method type with the given components |
Throws | |
---|---|
NullPointerException |
if rtype or ptypes is null |
public static MethodType methodType (Class<?> rtype, Class[]<?> ptypes)
Finds or creates an instance of the given method type.
Parameters | |
---|---|
rtype |
Class : the return type |
ptypes |
Class : the parameter types |
Returns | |
---|---|
MethodType |
a method type with the given components |
Throws | |
---|---|
NullPointerException |
if rtype or ptypes or any element of ptypes is null |
IllegalArgumentException |
if any element of ptypes is void.class |
public static MethodType methodType (Class<?> rtype, Class<?> ptype0)
Finds or creates a method type with the given components.
Convenience method for methodType
.
The resulting method has the single given parameter type.
Parameters | |
---|---|
rtype |
Class : the return type |
ptype0 |
Class : the parameter type |
Returns | |
---|---|
MethodType |
a method type with the given return value and parameter type |
Throws | |
---|---|
NullPointerException |
if rtype or ptype0 is null |
IllegalArgumentException |
if ptype0 is void.class |
public static MethodType methodType (Class<?> rtype)
Finds or creates a method type with the given components.
Convenience method for methodType
.
The resulting method has no parameter types.
Parameters | |
---|---|
rtype |
Class : the return type |
Returns | |
---|---|
MethodType |
a method type with the given return value |
Throws | |
---|---|
NullPointerException |
if rtype is null |
public static MethodType methodType (Class<?> rtype, List<Class<?>> ptypes)
Finds or creates a method type with the given components.
Convenience method for methodType
.
Parameters | |
---|---|
rtype |
Class : the return type |
ptypes |
List : the parameter types |
Returns | |
---|---|
MethodType |
a method type with the given components |
Throws | |
---|---|
NullPointerException |
if rtype or ptypes or any element of ptypes is null |
IllegalArgumentException |
if any element of ptypes is void.class |
public static MethodType methodType (Class<?> rtype, Class<?> ptype0, Class...<?> ptypes)
Finds or creates a method type with the given components.
Convenience method for methodType
.
The leading parameter type is prepended to the remaining array.
Parameters | |
---|---|
rtype |
Class : the return type |
ptype0 |
Class : the first parameter type |
ptypes |
Class : the remaining parameter types |
Returns | |
---|---|
MethodType |
a method type with the given components |
Throws | |
---|---|
NullPointerException |
if rtype or ptype0 or ptypes or any element of ptypes is null |
IllegalArgumentException |
if ptype0 or ptypes or any element of ptypes is void.class |
public Class[]<?> parameterArray ()
Presents the parameter types as an array (a convenience method). Changes to the array will not result in changes to the type.
Returns | |
---|---|
Class[]<?> |
the parameter types (as a fresh copy if necessary) |
public int parameterCount ()
Returns the number of parameter types in this method type.
Returns | |
---|---|
int |
the number of parameter types |
public List<Class<?>> parameterList ()
Presents the parameter types as a list (a convenience method). The list will be immutable.
Returns | |
---|---|
List<Class<?>> |
the parameter types (as an immutable list) |
public Class<?> parameterType (int num)
Returns the parameter type at the specified index, within this method type.
Parameters | |
---|---|
num |
int : the index (zero-based) of the desired parameter type |
Returns | |
---|---|
Class<?> |
the selected parameter type |
Throws | |
---|---|
IndexOutOfBoundsException |
if num is not a valid index into parameterArray() |
public Class<?> returnType ()
Returns the return type of this method type.
Returns | |
---|---|
Class<?> |
the return type |
public String toMethodDescriptorString ()
Produces a bytecode descriptor representation of the method type.
Note that this is not a strict inverse of fromMethodDescriptorString
.
Two distinct classes which share a common name but have different class loaders
will appear identical when viewed within descriptor strings.
This method is included for the benefit of applications that must
generate bytecodes that process method handles and invokedynamic
.
fromMethodDescriptorString
,
because the latter requires a suitable class loader argument.
Returns | |
---|---|
String |
the bytecode type descriptor representation |
public String toString ()
Returns a string representation of the method type,
of the form "(PT0,PT1...)RT"
.
The string representation of a method type is a
parenthesis enclosed, comma separated list of type names,
followed immediately by the return type.
Each type is represented by its
simple name
.
Returns | |
---|---|
String |
a string representation of the object. |
public MethodType unwrap ()
Converts all wrapper types to their corresponding primitive types.
Convenience method for methodType
.
All primitive types (including void
) will remain unchanged.
A return type of java.lang.Void
is changed to void
.
Returns | |
---|---|
MethodType |
a version of the original type with all wrapper types replaced |
public MethodType wrap ()
Converts all primitive types to their corresponding wrapper types.
Convenience method for methodType
.
All reference types (including wrapper types) will remain unchanged.
A void
return type is changed to the type java.lang.Void
.
The expression type.wrap().erase()
produces the same value
as type.generic()
.
Returns | |
---|---|
MethodType |
a version of the original type with all primitive types replaced |