Module java.base

Class 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.

Since:
1.1
See Also:
Member, Class, Class.getMethods(), Class.getMethod(String, Class[]), Class.getDeclaredMethods(), Class.getDeclaredMethod(String, Class[])
  • Method Details

    • setAccessible

      public void setAccessible​(boolean flag)
      Description copied from class: AccessibleObject
      Set the accessible flag for this reflected object to the indicated boolean value. A value of true indicates that the reflected object should suppress checks for Java language access control when it is used. A value of false indicates that the reflected object should enforce checks for Java language access control when it is used, with the variation noted in the class description.

      This method may be used by a caller in class C to enable access to a member of declaring class D if any of the following hold:

      • C and D are in the same module.
      • The member is public and D is public in a package that the module containing D exports to at least the module containing C.
      • The member is protected static, D is public in a package that the module containing D exports to at least the module containing C, and C is a subclass of D.
      • D is in a package that the module containing D opens to at least the module containing C. All packages in unnamed and open modules are open to all modules and so this method always succeeds when D is in an unnamed or open module.

      This method cannot be used to enable access to private members, members with default (package) access, protected instance members, or protected constructors when the declaring class is in a different module to the caller and the package containing the declaring class is not open to the caller's module.

      This method cannot be used to enable write access to a non-modifiable final field. The following fields are non-modifiable:

      • static final fields declared in any class or interface
      • final fields declared in a hidden class
      • final fields declared in a record

      The accessible flag when true suppresses Java language access control checks to only enable read access to these non-modifiable final fields.

      If there is a security manager, its checkPermission method is first called with a ReflectPermission("suppressAccessChecks") permission.

      Overrides:
      setAccessible in class AccessibleObject
      Parameters:
      flag - the new value for the accessible flag
      Throws:
      InaccessibleObjectException - if access cannot be enabled
      SecurityException - if the request is denied by the security manager
      See Also:
      AccessibleObject.trySetAccessible(), MethodHandles.privateLookupIn(java.lang.Class<?>, java.lang.invoke.MethodHandles.Lookup)
    • getDeclaringClass

      public Class<?> getDeclaringClass()
      Returns the Class object representing the class or interface that declares the method 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
    • 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 arguments 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
    • 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. Note that the constructors of some inner classes may have an implicitly declared parameter in addition to explicitly declared ones.

      If a formal parameter type is a parameterized type, the Type object returned for it must accurately reflect the actual type arguments 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 Types 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
    • 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 Java Language Specification:
      8.4.3 Method Modifiers
      9.4 Method Declarations
      9.6.1 Annotation Type Elements
    • 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, including informative bounds of the 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
      See Java Language Specification:
      8.4.3 Method Modifiers
      9.4 Method Declarations
      9.6.1 Annotation Type Elements
      Since:
      1.5
    • invoke

      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, section 15.12.4.4; in particular, overriding based on the runtime type of the target object may 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.
      See Java Language Specification:
      13.1 The Form of a Binary
      Since:
      1.5
    • 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.

      Note that any annotation returned by this method is a declaration annotation.

      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.

      Note that any annotations returned by this method are declaration annotations.

      Specified by:
      getDeclaredAnnotations in interface AnnotatedElement
      Overrides:
      getDeclaredAnnotations in class AccessibleObject
      Returns:
      annotations directly present on this element
      Since:
      1.5
    • getParameterAnnotations

      public Annotation[][] getParameterAnnotations()
      Returns an array of arrays of Annotations 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.

      Note that any annotations returned by this method are declaration annotations.

      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