Constructor (Java SE 11 & JDK 11 )
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Module java.base
Package java.lang.reflect
Class Constructor<T>
java.lang.Object
java.lang.reflect.AccessibleObject
java.lang.reflect.Executable
java.lang.reflect.Constructor<T>
Type Parameters:
T - the class in which the constructor is declared
All Implemented Interfaces:
AnnotatedElement, GenericDeclaration, Member
public final class Constructor<T>
extends Executable
Constructor provides information about, and access to, a single
constructor for a class.
Constructor permits widening conversions to occur when matching the
actual parameters to newInstance() with the underlying
constructor's formal parameters, but throws an
IllegalArgumentException if a narrowing conversion would occur.
Since:
1.1
See Also:
Member,
Class,
Class.getConstructors(),
Class.getConstructor(Class[]),
Class.getDeclaredConstructors()
Field Summary
Fields declared in interface java.lang.reflect.Member
DECLARED, PUBLIC
Method Summary
All Methods Instance Methods Concrete Methods 
Modifier and Type
Method
Description
boolean
equals​(Object obj)
Compares this Constructor against the specified object.
AnnotatedType
getAnnotatedReceiverType()
Returns an AnnotatedType object that represents the use of a
type to specify the receiver type of the method/constructor represented
by this Executable 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<T>
getDeclaringClass()
Returns the Class object representing the class that
declares the constructor 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.
String
getName()
Returns the name of this constructor, as a string.
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.
int
getParameterCount()
Returns the number of formal parameters (whether explicitly
declared or implicitly declared or neither) for the executable
represented by this object.
TypeVariable<Constructor<T>>[]
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 Constructor.
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.
T
newInstance​(Object... initargs)
Uses the constructor represented by this Constructor object to
create and initialize a new instance of the constructor's
declaring class, with the specified initialization parameters.
void
setAccessible​(boolean flag)
Set the accessible flag for this reflected object to
the indicated boolean value.
String
toGenericString()
Returns a string describing this Constructor,
including type parameters.
String
toString()
Returns a string describing this Constructor.
Methods declared in class java.lang.reflect.Executable
getAnnotatedExceptionTypes, getAnnotatedParameterTypes, getAnnotationsByType, getExceptionTypes, getModifiers, getParameters, getParameterTypes
Methods declared in class java.lang.reflect.AccessibleObject
canAccess, getAnnotations, getDeclaredAnnotation, getDeclaredAnnotationsByType, isAccessible, isAnnotationPresent, setAccessible, trySetAccessible
Methods declared in class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
Methods declared in interface java.lang.reflect.AnnotatedElement
getAnnotations, getDeclaredAnnotation, getDeclaredAnnotationsByType, isAnnotationPresent
Method Detail
setAccessible
public void setAccessible​(boolean flag)
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.
If there is a security manager, its
checkPermission method is first called with a
ReflectPermission("suppressAccessChecks") permission.
A SecurityException is also thrown if this object is a
Constructor object for the class Class and flag
is true.
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
or this is a constructor for java.lang.Class
See Also:
AccessibleObject.trySetAccessible(),
MethodHandles.privateLookupIn(java.lang.Class<?>, java.lang.invoke.MethodHandles.Lookup)
getDeclaringClass
public Class<T> getDeclaringClass()
Returns the Class object representing the class that
declares the constructor 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 this constructor, as a string.  This is
the binary name of the constructor's declaring class.
Specified by:
getName in interface Member
Specified by:
getName in class Executable
Returns:
the simple name of the underlying member
getTypeParameters
public TypeVariable<Constructor<T>>[] 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
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 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 Constructor against the specified object.
Returns true if the objects are the same.  Two Constructor objects are
the same if they were declared by the same class and have the
same formal parameter types.
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 Constructor. The hashcode is
the same as the hashcode for the underlying constructor's
declaring class 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 Constructor.  The string is
formatted as the constructor access modifiers, if any,
followed by the fully-qualified name of the declaring class,
followed by a parenthesized, comma-separated list of the
constructor's formal parameter types.  For example:
public java.util.Hashtable(int,float)
If the constructor 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
thrown exception types.
The only possible modifiers for constructors are the access
modifiers public, protected or
private.  Only one of these may appear, or none if the
constructor has default (package) access.
Overrides:
toString in class Object
Returns:
a string describing this Constructor
See The Java™ Language Specification:
8.8.3 Constructor Modifiers, 8.9.2 Enum Body Declarations
toGenericString
public String toGenericString()
Returns a string describing this Constructor,
including type parameters.  The string is formatted as the
constructor access modifiers, if any, followed by an
angle-bracketed comma separated list of the constructor's type
parameters, if any, followed by the fully-qualified name of the
declaring class, followed by a parenthesized, comma-separated
list of the constructor's generic formal parameter types.
If this constructor 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 class name.  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 constructor 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 only possible modifiers for constructors are the access
modifiers public, protected or
private.  Only one of these may appear, or none if the
constructor has default (package) access.
Specified by:
toGenericString in class Executable
Returns:
a string describing this Constructor,
include type parameters
Since:
1.5
See The Java™ Language Specification:
8.8.3 Constructor Modifiers, 8.9.2 Enum Body Declarations
newInstance
public T newInstance​(Object... initargs)
throws InstantiationException,
IllegalAccessException,
IllegalArgumentException,
InvocationTargetException
Uses the constructor represented by this Constructor object to
create and initialize a new instance of the constructor's
declaring class, with the specified initialization 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 number of formal parameters required by the underlying constructor
is 0, the supplied initargs array may be of length 0 or null.
If the constructor's declaring class is an inner class in a
non-static context, the first argument to the constructor needs
to be the enclosing instance; see section 15.9.3 of
The Java™ Language Specification.
If the required access and argument checks succeed and the
instantiation will proceed, the constructor's declaring class
is initialized if it has not already been initialized.
If the constructor completes normally, returns the newly
created and initialized instance.
Parameters:
initargs - array of objects to be passed as arguments to
the constructor call; values of primitive types are wrapped in
a wrapper object of the appropriate type (e.g. a float
in a Float)
Returns:
a new object created by calling the constructor
this object represents
Throws:
IllegalAccessException - if this Constructor object
is enforcing Java language access control and the underlying
constructor is inaccessible.
IllegalArgumentException - 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; if
this constructor pertains to an enum type.
InstantiationException - if the class that declares the
underlying constructor represents an abstract class.
InvocationTargetException - if the underlying constructor
throws an exception.
ExceptionInInitializerError - if the initialization provoked
by this method fails.
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
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 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.
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,
AnnotatedElement.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
getAnnotatedReceiverType
public AnnotatedType getAnnotatedReceiverType()
Returns an AnnotatedType object that represents the use of a
type to specify the receiver type of the method/constructor represented
by this Executable object.
The receiver type of a method/constructor is available only if the
method/constructor has a receiver parameter (JLS 8.4.1). If this
Executable object represents an instance method or represents a
constructor of an inner member class, and the
method/constructor either has no receiver parameter or has a
receiver parameter with no annotations on its type, then the return
value is an AnnotatedType object representing an element with no
annotations.
If this Executable object represents a static method or
represents a constructor of a top level, static member, local, or
anonymous class, then the return value is null.
Overrides:
getAnnotatedReceiverType in class Executable
Returns:
an object representing the receiver type of the method or
constructor represented by this Executable or null if
this Executable can not have a receiver parameter
Since:
1.8
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