- java.lang.Object
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- java.lang.invoke.MethodType
 
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- All Implemented Interfaces:
- Serializable
 
 public final class MethodType extends Object implements Serializable 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 toMethodHandle.invokeExactandMethodHandle.invoke, and during execution ofinvokedynamicinstructions.The structure is a return type accompanied by any number of parameter types. The types (primitive, void, and reference) are represented byClassobjects. (For ease of exposition, we treatvoidas if it were a type. In fact, it denotes the absence of a return type.)All instances of MethodTypeare 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 parameterArrayandparameterListalso provide a choice between arrays and lists.MethodTypeobjects are sometimes derived from bytecode instructions such asinvokedynamic, 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 ldcinstruction which refers to a suitableCONSTANT_MethodTypeconstant pool entry. The entry refers to aCONSTANT_Utf8spelling 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 MethodTypefrom 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 aCONSTANT_Class.) This loading may occur at any time before theMethodTypeobject is first derived.- Since:
- 1.7
- See Also:
- Serialized Form
 
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Method SummaryAll Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description MethodTypeappendParameterTypes(Class<?>... ptypesToInsert)Finds or creates a method type with additional parameter types.MethodTypeappendParameterTypes(List<Class<?>> ptypesToInsert)Finds or creates a method type with additional parameter types.MethodTypechangeParameterType(int num, Class<?> nptype)Finds or creates a method type with a single different parameter type.MethodTypechangeReturnType(Class<?> nrtype)Finds or creates a method type with a different return type.MethodTypedropParameterTypes(int start, int end)Finds or creates a method type with some parameter types omitted.booleanequals(Object x)Compares the specified object with this type for equality.MethodTypeerase()Erases all reference types toObject.static MethodTypefromMethodDescriptorString(String descriptor, ClassLoader loader)Finds or creates an instance of a method type, given the spelling of its bytecode descriptor.MethodTypegeneric()Converts all types, both reference and primitive, toObject.static MethodTypegenericMethodType(int objectArgCount)Finds or creates a method type whose components are allObject.static MethodTypegenericMethodType(int objectArgCount, boolean finalArray)Finds or creates a method type whose components areObjectwith an optional trailingObject[]array.inthashCode()Returns the hash code value for this method type.booleanhasPrimitives()Reports if this type contains a primitive argument or return value.booleanhasWrappers()Reports if this type contains a wrapper argument or return value.MethodTypeinsertParameterTypes(int num, Class<?>... ptypesToInsert)Finds or creates a method type with additional parameter types.MethodTypeinsertParameterTypes(int num, List<Class<?>> ptypesToInsert)Finds or creates a method type with additional parameter types.Class<?>lastParameterType()Returns the last parameter type of this method type.static MethodTypemethodType(Class<?> rtype)Finds or creates a method type with the given components.static MethodTypemethodType(Class<?> rtype, Class<?> ptype0)Finds or creates a method type with the given components.static MethodTypemethodType(Class<?> rtype, Class<?>[] ptypes)Finds or creates an instance of the given method type.static MethodTypemethodType(Class<?> rtype, Class<?> ptype0, Class<?>... ptypes)Finds or creates a method type with the given components.static MethodTypemethodType(Class<?> rtype, MethodType ptypes)Finds or creates a method type with the given components.static MethodTypemethodType(Class<?> rtype, List<Class<?>> ptypes)Finds or creates a method type with the given components.Class<?>[]parameterArray()Presents the parameter types as an array (a convenience method).intparameterCount()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.StringtoMethodDescriptorString()Produces a bytecode descriptor representation of the method type.StringtoString()Returns a string representation of the method type, of the form"(PT0,PT1...)RT".MethodTypeunwrap()Converts all wrapper types to their corresponding primitive types.MethodTypewrap()Converts all primitive types to their corresponding wrapper types.
 
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Method Detail- 
methodTypepublic static MethodType methodType(Class<?> rtype, Class<?>[] ptypes) Finds or creates an instance of the given method type.- Parameters:
- rtype- the return type
- ptypes- the parameter types
- Returns:
- a method type with the given components
- Throws:
- NullPointerException- if- rtypeor- ptypesor any element of- ptypesis null
- IllegalArgumentException- if any element of- ptypesis- void.class
 
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methodTypepublic static MethodType methodType(Class<?> rtype, List<Class<?>> ptypes) Finds or creates a method type with the given components. Convenience method formethodType.- Parameters:
- rtype- the return type
- ptypes- the parameter types
- Returns:
- a method type with the given components
- Throws:
- NullPointerException- if- rtypeor- ptypesor any element of- ptypesis null
- IllegalArgumentException- if any element of- ptypesis- void.class
 
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methodTypepublic static MethodType methodType(Class<?> rtype, Class<?> ptype0, Class<?>... ptypes) Finds or creates a method type with the given components. Convenience method formethodType. The leading parameter type is prepended to the remaining array.- Parameters:
- rtype- the return type
- ptype0- the first parameter type
- ptypes- the remaining parameter types
- Returns:
- a method type with the given components
- Throws:
- NullPointerException- if- rtypeor- ptype0or- ptypesor any element of- ptypesis null
- IllegalArgumentException- if- ptype0or- ptypesor any element of- ptypesis- void.class
 
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methodTypepublic static MethodType methodType(Class<?> rtype) Finds or creates a method type with the given components. Convenience method formethodType. The resulting method has no parameter types.- Parameters:
- rtype- the return type
- Returns:
- a method type with the given return value
- Throws:
- NullPointerException- if- rtypeis null
 
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methodTypepublic static MethodType methodType(Class<?> rtype, Class<?> ptype0) Finds or creates a method type with the given components. Convenience method formethodType. The resulting method has the single given parameter type.- Parameters:
- rtype- the return type
- ptype0- the parameter type
- Returns:
- a method type with the given return value and parameter type
- Throws:
- NullPointerException- if- rtypeor- ptype0is null
- IllegalArgumentException- if- ptype0is- void.class
 
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methodTypepublic static MethodType methodType(Class<?> rtype, MethodType ptypes) Finds or creates a method type with the given components. Convenience method formethodType. The resulting method has the same parameter types asptypes, and the specified return type.- Parameters:
- rtype- the return type
- ptypes- the method type which supplies the parameter types
- Returns:
- a method type with the given components
- Throws:
- NullPointerException- if- rtypeor- ptypesis null
 
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genericMethodTypepublic static MethodType genericMethodType(int objectArgCount, boolean finalArray) Finds or creates a method type whose components areObjectwith an optional trailingObject[]array. Convenience method formethodType. All parameters and the return type will beObject, except the final array parameter if any, which will beObject[].- Parameters:
- objectArgCount- number of parameters (excluding the final array parameter if any)
- finalArray- whether there will be a trailing array parameter, of type- Object[]
- Returns:
- a generally applicable method type, for all calls of the given fixed argument count and a collected array of further arguments
- Throws:
- IllegalArgumentException- if- objectArgCountis negative or greater than 255 (or 254, if- finalArrayis true)
- See Also:
- genericMethodType(int)
 
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genericMethodTypepublic static MethodType genericMethodType(int objectArgCount) Finds or creates a method type whose components are allObject. Convenience method formethodType. All parameters and the return type will be Object.- Parameters:
- objectArgCount- number of parameters
- Returns:
- a generally applicable method type, for all calls of the given argument count
- Throws:
- IllegalArgumentException- if- objectArgCountis negative or greater than 255
- See Also:
- genericMethodType(int, boolean)
 
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changeParameterTypepublic MethodType changeParameterType(int num, Class<?> nptype) Finds or creates a method type with a single different parameter type. Convenience method formethodType.- Parameters:
- num- the index (zero-based) of the parameter type to change
- nptype- a new parameter type to replace the old one with
- Returns:
- the same type, except with the selected parameter changed
- Throws:
- IndexOutOfBoundsException- if- numis not a valid index into- parameterArray()
- IllegalArgumentException- if- nptypeis- void.class
- NullPointerException- if- nptypeis null
 
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insertParameterTypespublic MethodType insertParameterTypes(int num, Class<?>... ptypesToInsert) Finds or creates a method type with additional parameter types. Convenience method formethodType.- Parameters:
- num- the position (zero-based) of the inserted parameter type(s)
- ptypesToInsert- zero or more new parameter types to insert into the parameter list
- Returns:
- the same type, except with the selected parameter(s) inserted
- Throws:
- IndexOutOfBoundsException- if- numis negative or greater than- parameterCount()
- IllegalArgumentException- if any element of- ptypesToInsertis- void.classor if the resulting method type would have more than 255 parameter slots
- NullPointerException- if- ptypesToInsertor any of its elements is null
 
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appendParameterTypespublic MethodType appendParameterTypes(Class<?>... ptypesToInsert) Finds or creates a method type with additional parameter types. Convenience method formethodType.- Parameters:
- ptypesToInsert- zero or more new parameter types to insert after the end of the parameter list
- Returns:
- the same type, except with the selected parameter(s) appended
- Throws:
- IllegalArgumentException- if any element of- ptypesToInsertis- void.classor if the resulting method type would have more than 255 parameter slots
- NullPointerException- if- ptypesToInsertor any of its elements is null
 
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insertParameterTypespublic MethodType insertParameterTypes(int num, List<Class<?>> ptypesToInsert) Finds or creates a method type with additional parameter types. Convenience method formethodType.- Parameters:
- num- the position (zero-based) of the inserted parameter type(s)
- ptypesToInsert- zero or more new parameter types to insert into the parameter list
- Returns:
- the same type, except with the selected parameter(s) inserted
- Throws:
- IndexOutOfBoundsException- if- numis negative or greater than- parameterCount()
- IllegalArgumentException- if any element of- ptypesToInsertis- void.classor if the resulting method type would have more than 255 parameter slots
- NullPointerException- if- ptypesToInsertor any of its elements is null
 
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appendParameterTypespublic MethodType appendParameterTypes(List<Class<?>> ptypesToInsert) Finds or creates a method type with additional parameter types. Convenience method formethodType.- Parameters:
- ptypesToInsert- zero or more new parameter types to insert after the end of the parameter list
- Returns:
- the same type, except with the selected parameter(s) appended
- Throws:
- IllegalArgumentException- if any element of- ptypesToInsertis- void.classor if the resulting method type would have more than 255 parameter slots
- NullPointerException- if- ptypesToInsertor any of its elements is null
 
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dropParameterTypespublic MethodType dropParameterTypes(int start, int end) Finds or creates a method type with some parameter types omitted. Convenience method formethodType.- Parameters:
- start- the index (zero-based) of the first parameter type to remove
- end- the index (greater than- start) of the first parameter type after not to remove
- Returns:
- the same type, except with the selected parameter(s) removed
- Throws:
- IndexOutOfBoundsException- if- startis negative or greater than- parameterCount()or if- endis negative or greater than- parameterCount()or if- startis greater than- end
 
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changeReturnTypepublic MethodType changeReturnType(Class<?> nrtype) Finds or creates a method type with a different return type. Convenience method formethodType.- Parameters:
- nrtype- a return parameter type to replace the old one with
- Returns:
- the same type, except with the return type change
- Throws:
- NullPointerException- if- nrtypeis null
 
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hasPrimitivespublic boolean hasPrimitives() Reports if this type contains a primitive argument or return value. The return typevoidcounts as a primitive.- Returns:
- true if any of the types are primitives
 
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hasWrapperspublic boolean hasWrappers() Reports if this type contains a wrapper argument or return value. Wrappers are types which box primitive values, such asInteger. The reference typejava.lang.Voidcounts as a wrapper, if it occurs as a return type.- Returns:
- true if any of the types are wrappers
 
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erasepublic MethodType erase() Erases all reference types toObject. Convenience method formethodType. All primitive types (includingvoid) will remain unchanged.- Returns:
- a version of the original type with all reference types replaced
 
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genericpublic MethodType generic() Converts all types, both reference and primitive, toObject. Convenience method forgenericMethodType. The expressiontype.wrap().erase()produces the same value astype.generic().- Returns:
- a version of the original type with all types replaced
 
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wrappublic MethodType wrap() Converts all primitive types to their corresponding wrapper types. Convenience method formethodType. All reference types (including wrapper types) will remain unchanged. Avoidreturn type is changed to the typejava.lang.Void. The expressiontype.wrap().erase()produces the same value astype.generic().- Returns:
- a version of the original type with all primitive types replaced
 
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unwrappublic MethodType unwrap() Converts all wrapper types to their corresponding primitive types. Convenience method formethodType. All primitive types (includingvoid) will remain unchanged. A return type ofjava.lang.Voidis changed tovoid.- Returns:
- a version of the original type with all wrapper types replaced
 
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parameterTypepublic Class<?> parameterType(int num) Returns the parameter type at the specified index, within this method type.- Parameters:
- num- the index (zero-based) of the desired parameter type
- Returns:
- the selected parameter type
- Throws:
- IndexOutOfBoundsException- if- numis not a valid index into- parameterArray()
 
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parameterCountpublic int parameterCount() Returns the number of parameter types in this method type.- Returns:
- the number of parameter types
 
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returnTypepublic Class<?> returnType() Returns the return type of this method type.- Returns:
- the return type
 
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parameterListpublic List<Class<?>> parameterList() Presents the parameter types as a list (a convenience method). The list will be immutable.- Returns:
- the parameter types (as an immutable list)
 
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lastParameterTypepublic Class<?> lastParameterType() Returns the last parameter type of this method type. If this type has no parameters, the sentinel valuevoid.classis returned instead.- API Note:
- The sentinel value is chosen so that reflective queries can be made directly against the result value. The sentinel value cannot be confused with a real parameter, since - voidis never acceptable as a parameter type. For variable arity invocation modes, the expression- lastParameterType().getComponentType()is useful to query the type of the "varargs" parameter.
- Returns:
- the last parameter type if any, else void.class
- Since:
- 10
 
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parameterArraypublic 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:
- the parameter types (as a fresh copy if necessary)
 
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equalspublic boolean equals(Object x) Compares the specified object with this type for equality. That is, it returnstrueif and only if the specified object is also a method type with exactly the same parameters and return type.- Overrides:
- equalsin class- Object
- Parameters:
- x- object to compare
- Returns:
- trueif this object is the same as the obj argument;- falseotherwise.
- See Also:
- Object.equals(Object)
 
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hashCodepublic 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.- Overrides:
- hashCodein class- Object
- Returns:
- the hash code value for this method type
- See Also:
- Object.hashCode(),- equals(Object),- List.hashCode()
 
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toStringpublic 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.
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fromMethodDescriptorStringpublic static MethodType fromMethodDescriptorString(String descriptor, ClassLoader loader) throws IllegalArgumentException, TypeNotPresentException Finds or creates an instance of a method type, given the spelling of its bytecode descriptor. Convenience method formethodType. Any class or interface name embedded in the descriptor string will be resolved by callingClassLoader.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- a bytecode-level type descriptor string "(T...)T"
- loader- the class loader in which to look up the types
- Returns:
- 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
 
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toMethodDescriptorStringpublic 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:
- the bytecode type descriptor representation
 
 
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