Method (Java Platform SE 8 )
Keywords: java.lang.reflect.Method class
Date: 2020-03-26

compact1, compact2, compact3
java.lang.reflect

## Class Method

- java.lang.Object
- - java.lang.reflect.AccessibleObject
  - - java.lang.reflect.Executable
    - - java.lang.reflect.Method

- All Implemented Interfaces:
    AnnotatedElement, GenericDeclaration, Member

      public final class Method
      extends Executable

  A `Method` provides information about, and access to, a single method on a class or interface. The reflected method may be a class method or an instance method (including an abstract method).

  A `Method` permits widening conversions to occur when matching the actual parameters to invoke with the underlying method's formal parameters, but it throws an `IllegalArgumentException` if a narrowing conversion would occur.

  See Also:
    `Member`, `Class`, `Class.getMethods()`, `Class.getMethod(String, Class[])`, `Class.getDeclaredMethods()`, `Class.getDeclaredMethod(String, Class[])`

- - ### Field Summary

    - ### Fields inherited from interface java.lang.reflect.Member

      `DECLARED, PUBLIC`

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `boolean` | `equals(Object obj)` Compares this `Method` against the specified object.
    `AnnotatedType` | `getAnnotatedReturnType()` Returns an `AnnotatedType` object that represents the use of a type to specify the return type of the method/constructor represented by this Executable.
    `<T extends Annotation> T` | `getAnnotation(Class<T> annotationClass)` Returns this element's annotation for the specified type if such an annotation is present, else null.
    `Annotation[]` | `getDeclaredAnnotations()` Returns annotations that are directly present on this element.
    `Class<?>` | `getDeclaringClass()` Returns the `Class` object representing the class or interface that declares the executable represented by this object.
    `Object` | `getDefaultValue()` Returns the default value for the annotation member represented by this `Method` instance.
    `Class<?>[]` | `getExceptionTypes()` Returns an array of `Class` objects that represent the types of exceptions declared to be thrown by the underlying executable represented by this object.
    `Type[]` | `getGenericExceptionTypes()` Returns an array of `Type` objects that represent the exceptions declared to be thrown by this executable object.
    `Type[]` | `getGenericParameterTypes()` Returns an array of `Type` objects that represent the formal parameter types, in declaration order, of the executable represented by this object.
    `Type` | `getGenericReturnType()` Returns a `Type` object that represents the formal return type of the method represented by this `Method` object.
    `int` | `getModifiers()` Returns the Java language modifiers for the executable represented by this object.
    `String` | `getName()` Returns the name of the method represented by this `Method` object, as a `String`.
    `Annotation[][]` | `getParameterAnnotations()` Returns an array of arrays of `Annotation`s that represent the annotations on the formal parameters, in declaration order, of the `Executable` represented by this object.
    `int` | `getParameterCount()` Returns the number of formal parameters (whether explicitly declared or implicitly declared or neither) for the executable represented by this object.
    `Class<?>[]` | `getParameterTypes()` Returns an array of `Class` objects that represent the formal parameter types, in declaration order, of the executable represented by this object.
    `Class<?>` | `getReturnType()` Returns a `Class` object that represents the formal return type of the method represented by this `Method` object.
    `TypeVariable<Method>[]` | `getTypeParameters()` Returns an array of `TypeVariable` objects that represent the type variables declared by the generic declaration represented by this `GenericDeclaration` object, in declaration order.
    `int` | `hashCode()` Returns a hashcode for this `Method`.
    `Object` | `invoke(Object obj, Object... args)` Invokes the underlying method represented by this `Method` object, on the specified object with the specified parameters.
    `boolean` | `isBridge()` Returns `true` if this method is a bridge method; returns `false` otherwise.
    `boolean` | `isDefault()` Returns `true` if this method is a default method; returns `false` otherwise.
    `boolean` | `isSynthetic()` Returns `true` if this executable is a synthetic construct; returns `false` otherwise.
    `boolean` | `isVarArgs()` Returns `true` if this executable was declared to take a variable number of arguments; returns `false` otherwise.
    `String` | `toGenericString()` Returns a string describing this `Method`, including type parameters.
    `String` | `toString()` Returns a string describing this `Method`.

    - ### Methods inherited from class java.lang.reflect.Executable

      `getAnnotatedExceptionTypes, getAnnotatedParameterTypes, getAnnotatedReceiverType, getAnnotationsByType, getParameters`

    - ### Methods inherited from class java.lang.reflect.AccessibleObject

      `getAnnotations, getDeclaredAnnotation, getDeclaredAnnotationsByType, isAccessible, isAnnotationPresent, setAccessible, setAccessible`

    - ### Methods inherited from class java.lang.Object

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

    - ### Methods inherited from interface java.lang.reflect.AnnotatedElement

      `getAnnotations, getDeclaredAnnotation, getDeclaredAnnotationsByType, isAnnotationPresent`

- - ### Method Detail

    - #### getDeclaringClass

          public Class<?> getDeclaringClass()

      Returns the `Class` object representing the class or interface that declares the executable represented by this object.
      Specified by:
        `getDeclaringClass` in interface `Member`
      Specified by:
        `getDeclaringClass` in class `Executable`
      Returns:
        an object representing the declaring class of the underlying member

    - #### getName

          public String getName()

      Returns the name of the method represented by this `Method` object, as a `String`.
      Specified by:
        `getName` in interface `Member`
      Specified by:
        `getName` in class `Executable`
      Returns:
        the simple name of the underlying member

    - #### getModifiers

          public int getModifiers()

      Returns the Java language modifiers for the executable represented by this object.
      Specified by:
        `getModifiers` in interface `Member`
      Specified by:
        `getModifiers` in class `Executable`
      Returns:
        the Java language modifiers for the underlying member
      See Also:
        `Modifier`

    - #### getTypeParameters

          public TypeVariable<Method>[] getTypeParameters()

      Returns an array of `TypeVariable` objects that represent the type variables declared by the generic declaration represented by this `GenericDeclaration` object, in declaration order. Returns an array of length 0 if the underlying generic declaration declares no type variables.
      Specified by:
        `getTypeParameters` in interface `GenericDeclaration`
      Specified by:
        `getTypeParameters` in class `Executable`
      Returns:
        an array of `TypeVariable` objects that represent the type variables declared by this generic declaration
      Throws:
        `GenericSignatureFormatError` - if the generic signature of this generic declaration does not conform to the format specified in The Java™ Virtual Machine Specification
      Since:
        1.5

    - #### getReturnType

          public Class<?> getReturnType()

      Returns a `Class` object that represents the formal return type of the method represented by this `Method` object.
      Returns:
        the return type for the method this object represents

    - #### getGenericReturnType

          public Type getGenericReturnType()

      Returns a `Type` object that represents the formal return type of the method represented by this `Method` object.

      If the return type is a parameterized type, the `Type` object returned must accurately reflect the actual type parameters used in the source code.

      If the return type is a type variable or a parameterized type, it is created. Otherwise, it is resolved.

      Returns:
        a `Type` object that represents the formal return type of the underlying method
      Throws:
        `GenericSignatureFormatError` - if the generic method signature does not conform to the format specified in The Java™ Virtual Machine Specification
        `TypeNotPresentException` - if the underlying method's return type refers to a non-existent type declaration
        `MalformedParameterizedTypeException` - if the underlying method's return typed refers to a parameterized type that cannot be instantiated for any reason
      Since:
        1.5

    - #### getParameterTypes

          public Class<?>[] getParameterTypes()

      Returns an array of `Class` objects that represent the formal parameter types, in declaration order, of the executable represented by this object. Returns an array of length 0 if the underlying executable takes no parameters.
      Specified by:
        `getParameterTypes` in class `Executable`
      Returns:
        the parameter types for the executable this object represents

    - #### getParameterCount

          public int getParameterCount()

      Returns the number of formal parameters (whether explicitly declared or implicitly declared or neither) for the executable represented by this object.
      Overrides:
        `getParameterCount` in class `Executable`
      Returns:
        The number of formal parameters for the executable this object represents
      Since:
        1.8

    - #### getGenericParameterTypes

          public Type[] getGenericParameterTypes()

      Returns an array of `Type` objects that represent the formal parameter types, in declaration order, of the executable represented by this object. Returns an array of length 0 if the underlying executable takes no parameters.

      If a formal parameter type is a parameterized type, the `Type` object returned for it must accurately reflect the actual type parameters used in the source code.

      If a formal parameter type is a type variable or a parameterized type, it is created. Otherwise, it is resolved.

      Overrides:
        `getGenericParameterTypes` in class `Executable`
      Returns:
        an array of `Type`s that represent the formal parameter types of the underlying executable, in declaration order
      Throws:
        `GenericSignatureFormatError` - if the generic method signature does not conform to the format specified in The Java™ Virtual Machine Specification
        `TypeNotPresentException` - if any of the parameter types of the underlying executable refers to a non-existent type declaration
        `MalformedParameterizedTypeException` - if any of the underlying executable's parameter types refer to a parameterized type that cannot be instantiated for any reason
      Since:
        1.5

    - #### getExceptionTypes

          public Class<?>[] getExceptionTypes()

      Returns an array of `Class` objects that represent the types of exceptions declared to be thrown by the underlying executable represented by this object. Returns an array of length 0 if the executable declares no exceptions in its `throws` clause.
      Specified by:
        `getExceptionTypes` in class `Executable`
      Returns:
        the exception types declared as being thrown by the executable this object represents

    - #### getGenericExceptionTypes

          public Type[] getGenericExceptionTypes()

      Returns an array of `Type` objects that represent the exceptions declared to be thrown by this executable object. Returns an array of length 0 if the underlying executable declares no exceptions in its `throws` clause.

      If an exception type is a type variable or a parameterized type, it is created. Otherwise, it is resolved.

      Overrides:
        `getGenericExceptionTypes` in class `Executable`
      Returns:
        an array of Types that represent the exception types thrown by the underlying executable
      Throws:
        `GenericSignatureFormatError` - if the generic method signature does not conform to the format specified in The Java™ Virtual Machine Specification
        `TypeNotPresentException` - if the underlying executable's `throws` clause refers to a non-existent type declaration
        `MalformedParameterizedTypeException` - if the underlying executable's `throws` clause refers to a parameterized type that cannot be instantiated for any reason
      Since:
        1.5

    - #### equals

          public boolean equals(Object obj)

      Compares this `Method` against the specified object. Returns true if the objects are the same. Two `Methods` are the same if they were declared by the same class and have the same name and formal parameter types and return type.
      Overrides:
        `equals` in class `Object`
      Parameters:
        `obj` - the reference object with which to compare.
      Returns:
        `true` if this object is the same as the obj argument; `false` otherwise.
      See Also:
        `Object.hashCode()`, `HashMap`

    - #### hashCode

          public int hashCode()

      Returns a hashcode for this `Method`. The hashcode is computed as the exclusive-or of the hashcodes for the underlying method's declaring class name and the method's name.
      Overrides:
        `hashCode` in class `Object`
      Returns:
        a hash code value for this object.
      See Also:
        `Object.equals(java.lang.Object)`, `System.identityHashCode(java.lang.Object)`

    - #### toString

          public String toString()

      Returns a string describing this `Method`. The string is formatted as the method access modifiers, if any, followed by the method return type, followed by a space, followed by the class declaring the method, followed by a period, followed by the method name, followed by a parenthesized, comma-separated list of the method's formal parameter types. If the method throws checked exceptions, the parameter list is followed by a space, followed by the word throws followed by a comma-separated list of the thrown exception types. For example:

              public boolean java.lang.Object.equals(java.lang.Object)

      The access modifiers are placed in canonical order as specified by "The Java Language Specification". This is `public`, `protected` or `private` first, and then other modifiers in the following order: `abstract`, `default`, `static`, `final`, `synchronized`, `native`, `strictfp`.

      Overrides:
        `toString` in class `Object`
      Returns:
        a string describing this `Method`
      See The Java™ Language Specification:
        8.4.3 Method Modifiers

    - #### toGenericString

          public String toGenericString()

      Returns a string describing this `Method`, including type parameters. The string is formatted as the method access modifiers, if any, followed by an angle-bracketed comma-separated list of the method's type parameters, if any, followed by the method's generic return type, followed by a space, followed by the class declaring the method, followed by a period, followed by the method name, followed by a parenthesized, comma-separated list of the method's generic formal parameter types. If this method was declared to take a variable number of arguments, instead of denoting the last parameter as "`Type[]`", it is denoted as "`Type...`". A space is used to separate access modifiers from one another and from the type parameters or return type. If there are no type parameters, the type parameter list is elided; if the type parameter list is present, a space separates the list from the class name. If the method is declared to throw exceptions, the parameter list is followed by a space, followed by the word throws followed by a comma-separated list of the generic thrown exception types.

      The access modifiers are placed in canonical order as specified by "The Java Language Specification". This is `public`, `protected` or `private` first, and then other modifiers in the following order: `abstract`, `default`, `static`, `final`, `synchronized`, `native`, `strictfp`.

      Specified by:
        `toGenericString` in class `Executable`
      Returns:
        a string describing this `Method`, include type parameters
      Since:
        1.5
      See The Java™ Language Specification:
        8.4.3 Method Modifiers

    - #### invoke

          public Object invoke(Object obj,
                               Object... args)
                        throws IllegalAccessException,
                               IllegalArgumentException,
                               InvocationTargetException

      Invokes the underlying method represented by this `Method` object, on the specified object with the specified parameters. Individual parameters are automatically unwrapped to match primitive formal parameters, and both primitive and reference parameters are subject to method invocation conversions as necessary.

      If the underlying method is static, then the specified `obj` argument is ignored. It may be null.

      If the number of formal parameters required by the underlying method is 0, the supplied `args` array may be of length 0 or null.

      If the underlying method is an instance method, it is invoked using dynamic method lookup as documented in The Java Language Specification, Second Edition, section 15.12.4.4; in particular, overriding based on the runtime type of the target object will occur.

      If the underlying method is static, the class that declared the method is initialized if it has not already been initialized.

      If the method completes normally, the value it returns is returned to the caller of invoke; if the value has a primitive type, it is first appropriately wrapped in an object. However, if the value has the type of an array of a primitive type, the elements of the array are not wrapped in objects; in other words, an array of primitive type is returned. If the underlying method return type is void, the invocation returns null.

      Parameters:
        `obj` - the object the underlying method is invoked from
        `args` - the arguments used for the method call
      Returns:
        the result of dispatching the method represented by this object on `obj` with parameters `args`
      Throws:
        `IllegalAccessException` - if this `Method` object is enforcing Java language access control and the underlying method is inaccessible.
        `IllegalArgumentException` - if the method is an instance method and the specified object argument is not an instance of the class or interface declaring the underlying method (or of a subclass or implementor thereof); if the number of actual and formal parameters differ; if an unwrapping conversion for primitive arguments fails; or if, after possible unwrapping, a parameter value cannot be converted to the corresponding formal parameter type by a method invocation conversion.
        `InvocationTargetException` - if the underlying method throws an exception.
        `NullPointerException` - if the specified object is null and the method is an instance method.
        `ExceptionInInitializerError` - if the initialization provoked by this method fails.

    - #### isBridge

          public boolean isBridge()

      Returns `true` if this method is a bridge method; returns `false` otherwise.
      Returns:
        true if and only if this method is a bridge method as defined by the Java Language Specification.
      Since:
        1.5

    - #### isVarArgs

          public boolean isVarArgs()

      Returns `true` if this executable was declared to take a variable number of arguments; returns `false` otherwise.
      Overrides:
        `isVarArgs` in class `Executable`
      Returns:
        `true` if an only if this executable was declared to take a variable number of arguments.
      Since:
        1.5

    - #### isSynthetic

          public boolean isSynthetic()

      Returns `true` if this executable is a synthetic construct; returns `false` otherwise.
      Specified by:
        `isSynthetic` in interface `Member`
      Overrides:
        `isSynthetic` in class `Executable`
      Returns:
        true if and only if this executable is a synthetic construct as defined by The Java™ Language Specification.
      Since:
        1.5
      See The Java™ Language Specification:
        13.1 The Form of a Binary

    - #### isDefault

          public boolean isDefault()

      Returns `true` if this method is a default method; returns `false` otherwise. A default method is a public non-abstract instance method, that is, a non-static method with a body, declared in an interface type.
      Returns:
        true if and only if this method is a default method as defined by the Java Language Specification.
      Since:
        1.8

    - #### getDefaultValue

          public Object getDefaultValue()

      Returns the default value for the annotation member represented by this `Method` instance. If the member is of a primitive type, an instance of the corresponding wrapper type is returned. Returns null if no default is associated with the member, or if the method instance does not represent a declared member of an annotation type.
      Returns:
        the default value for the annotation member represented by this `Method` instance.
      Throws:
        `TypeNotPresentException` - if the annotation is of type `Class` and no definition can be found for the default class value.
      Since:
        1.5

    - #### getAnnotation

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

      Returns this element's annotation for the specified type if such an annotation is present, else null.
      Specified by:
        `getAnnotation` in interface `AnnotatedElement`
      Overrides:
        `getAnnotation` in class `Executable`
      Type Parameters:
        `T` - the type of the annotation to query for and return if present
      Parameters:
        `annotationClass` - the Class object corresponding to the annotation type
      Returns:
        this element's annotation for the specified annotation type if present on this element, else null
      Throws:
        `NullPointerException` - if the given annotation class is null
      Since:
        1.5

    - #### getDeclaredAnnotations

          public Annotation[] getDeclaredAnnotations()

      Returns annotations that are directly present on this element. This method ignores inherited annotations. If there are no annotations directly present on this element, the return value is an array of length 0. The caller of this method is free to modify the returned array; it will have no effect on the arrays returned to other callers.
      Specified by:
        `getDeclaredAnnotations` in interface `AnnotatedElement`
      Overrides:
        `getDeclaredAnnotations` in class `Executable`
      Returns:
        annotations directly present on this element
      Since:
        1.5

    - #### getParameterAnnotations

          public Annotation[][] getParameterAnnotations()

      Returns an array of arrays of `Annotation`s that represent the annotations on the formal parameters, in declaration order, of the `Executable` represented by this object. Synthetic and mandated parameters (see explanation below), such as the outer "this" parameter to an inner class constructor will be represented in the returned array. If the executable has no parameters (meaning no formal, no synthetic, and no mandated parameters), a zero-length array will be returned. If the `Executable` has one or more parameters, a nested array of length zero is returned for each parameter with no annotations. The annotation objects contained in the returned arrays are serializable. The caller of this method is free to modify the returned arrays; it will have no effect on the arrays returned to other callers. A compiler may add extra parameters that are implicitly declared in source ("mandated"), as well as parameters that are neither implicitly nor explicitly declared in source ("synthetic") to the parameter list for a method. See `Parameter` for more information.
      Specified by:
        `getParameterAnnotations` in class `Executable`
      Returns:
        an array of arrays that represent the annotations on the formal and implicit parameters, in declaration order, of the executable represented by this object
      Since:
        1.5
      See Also:
        `Parameter`, `Parameter.getAnnotations()`

    - #### getAnnotatedReturnType

          public AnnotatedType getAnnotatedReturnType()

      Returns an `AnnotatedType` object that represents the use of a type to specify the return type of the method/constructor represented by this Executable. If this `Executable` object represents a constructor, the `AnnotatedType` object represents the type of the constructed object. If this `Executable` object represents a method, the `AnnotatedType` object represents the use of a type to specify the return type of the method.
      Specified by:
        `getAnnotatedReturnType` in class `Executable`
      Returns:
        an object representing the return type of the method or constructor represented by this `Executable`
      Since:
        1.8

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