java.lang.reflect

Class Constructor<T>

java.lang.Object

java.lang.reflect.AccessibleObject

java.lang.reflect.Constructor<T>

All Implemented Interfaces:

AnnotatedElement, GenericDeclaration, Member

public final class Constructor<T>
extends AccessibleObject
implements GenericDeclaration, Member

The Constructor class represents a constructor of a class. It also allows dynamic creation of an object, via reflection. Invocation on Constructor objects knows how to do widening conversions, but throws IllegalArgumentException if a narrowing conversion would be necessary. You can query for information on this Constructor regardless of location, but construction access may be limited by Java language access controls. If you can't do it in the compiler, you can't normally do it here either.

Note: This class returns and accepts types as Classes, even primitive types; there are Class types defined that represent each different primitive type. They are java.lang.Boolean.TYPE, java.lang.Byte.TYPE,, also available as boolean.class, byte.class, etc. These are not to be confused with the classes java.lang.Boolean, java.lang.Byte, etc., which are real classes.

Also note that this is not a serializable class. It is entirely feasible to make it serializable using the Externalizable interface, but this is on Sun, not me.

Since:

1.1

See Also:

Member, Class, Class.getConstructor(Class[]), Class.getDeclaredConstructor(Class[]), Class.getConstructors(), Class.getDeclaredConstructors()

Field Summary

Fields inherited from interface java.lang.reflect.Member

DECLARED, PUBLIC

Method Summary

Methods

Modifier and Type	Method and Description
boolean	equals(java.lang.Object o) Compare two objects to see if they are semantically equivalent.
<T extends java.lang.annotation.Annotation> T	getAnnotation(java.lang.Class<T> annotationClass) Returns the element's annotation for the specified annotation type, or null if no such annotation exists.
java.lang.annotation.Annotation[]	getDeclaredAnnotations() Returns all annotations directly defined by the element.
java.lang.Class<T>	getDeclaringClass() Gets the class that declared this constructor.
java.lang.Class<?>[]	getExceptionTypes() Get the exception types this constructor says it throws, in no particular order.
Type[]	getGenericExceptionTypes() Returns an array of Type objects that represents the exception types declared by this constructor, in declaration order.
Type[]	getGenericParameterTypes() Returns an array of Type objects that represents the parameter list for this constructor, in declaration order.
int	getModifiers() Gets the modifiers this constructor uses.
java.lang.String	getName() Gets the name of this constructor (the non-qualified name of the class it was declared in).
java.lang.annotation.Annotation[][]	getParameterAnnotations() Return an array of arrays representing the annotations on each of the constructor's parameters.
java.lang.Class<?>[]	getParameterTypes() Get the parameter list for this constructor, in declaration order.
TypeVariable<Constructor<T>>[]	getTypeParameters() Returns an array of TypeVariable objects that represents the type variables declared by this constructor, in declaration order.
int	hashCode() Get the hash code for the Constructor.
boolean	isSynthetic() Return true if this constructor is synthetic, false otherwise.
boolean	isVarArgs() Return true if this is a varargs constructor, that is if the constructor takes a variable number of arguments.
T	newInstance(java.lang.Object... args) Create a new instance by invoking the constructor.
java.lang.String	toGenericString()
java.lang.String	toString() Get a String representation of the Constructor.

Methods inherited from class java.lang.reflect.AccessibleObject

getAnnotations, isAccessible, isAnnotationPresent, setAccessible, setAccessible

Methods inherited from class java.lang.Object

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

Method Detail

getDeclaringClass

public java.lang.Class<T> getDeclaringClass()

Gets the class that declared this constructor.

Specified by:

getDeclaringClass in interface Member

Returns:

the class that declared this member

getName

public java.lang.String getName()

Gets the name of this constructor (the non-qualified name of the class it was declared in).

Specified by:

getName in interface Member

Returns:

the name of this constructor

getModifiers

public int getModifiers()

Gets the modifiers this constructor uses. Use the Modifier class to interpret the values. A constructor can only have a subset of the following modifiers: public, private, protected.

Specified by:

getModifiers in interface Member

Returns:

an integer representing the modifiers to this Member

See Also:

Modifier

isSynthetic

public boolean isSynthetic()

Return true if this constructor is synthetic, false otherwise. A synthetic member is one which is created by the compiler, and which does not appear in the user's source code.

Specified by:

isSynthetic in interface Member

Returns:

true if the member is synthetic

Since:

1.5

isVarArgs

public boolean isVarArgs()

Return true if this is a varargs constructor, that is if the constructor takes a variable number of arguments.

Since:

1.5

getParameterTypes

public java.lang.Class<?>[] getParameterTypes()

Get the parameter list for this constructor, in declaration order. If the constructor takes no parameters, returns a 0-length array (not null).

Returns:

a list of the types of the constructor's parameters

getExceptionTypes

public java.lang.Class<?>[] getExceptionTypes()

Get the exception types this constructor says it throws, in no particular order. If the constructor has no throws clause, returns a 0-length array (not null).

Returns:

a list of the types in the constructor's throws clause

equals

public boolean equals(java.lang.Object o)

Compare two objects to see if they are semantically equivalent. Two Constructors are semantically equivalent if they have the same declaring class and the same parameter list. This ignores different exception clauses, but since you can't create a Method except through the VM, this is just the == relation.

Overrides:

equals in class java.lang.Object

Parameters:

o - the object to compare to

Returns:

true if they are equal; false if not.

See Also:

Object.hashCode()

hashCode

public int hashCode()

Get the hash code for the Constructor. The Constructor hash code is the hash code of the declaring class's name.

Overrides:

hashCode in class java.lang.Object

Returns:

the hash code for the object

See Also:

Object.equals(Object), System.identityHashCode(Object)

toString

public java.lang.String toString()

Get a String representation of the Constructor. A Constructor's String representation is "<modifier> <classname>(<paramtypes>) throws <exceptions>", where everything after ')' is omitted if there are no exceptions.
Example: public java.io.FileInputStream(java.lang.Runnable) throws java.io.FileNotFoundException

Overrides:

toString in class java.lang.Object

Returns:

the String representation of the Constructor

See Also:

Object.getClass(), Object.hashCode(), Class.getName(), Integer.toHexString(int)

toGenericString

public java.lang.String toGenericString()

newInstance

public T newInstance(java.lang.Object... args)
              throws java.lang.InstantiationException,
                     java.lang.IllegalAccessException,
                     InvocationTargetException

Create a new instance by invoking the constructor. Arguments are automatically unwrapped and widened, if needed.

If this class is abstract, you will get an InstantiationException. If the constructor takes 0 arguments, you may use null or a 0-length array for args.

If this Constructor enforces access control, your runtime context is evaluated, and you may have an IllegalAccessException if you could not create this object in similar compiled code. If the class is uninitialized, you trigger class initialization, which may end in a ExceptionInInitializerError.

Then, the constructor is invoked. If it completes normally, the return value will be the new object. If it completes abruptly, the exception is wrapped in an InvocationTargetException.

Parameters:

args - the arguments to the constructor

Returns:

the newly created object

Throws:

java.lang.IllegalAccessException - if the constructor could not normally be called by the Java code (i.e. it is not public)

java.lang.IllegalArgumentException - if the number of arguments is incorrect; or if the arguments types are wrong even with a widening conversion

java.lang.InstantiationException - if the class is abstract

InvocationTargetException - if the constructor throws an exception

java.lang.ExceptionInInitializerError - if construction triggered class initialization, which then failed

getTypeParameters

public TypeVariable<Constructor<T>>[] getTypeParameters()

Returns an array of TypeVariable objects that represents the type variables declared by this constructor, in declaration order. An array of size zero is returned if this constructor has no type variables.

Specified by:

getTypeParameters in interface GenericDeclaration

Returns:

the type variables associated with this constructor.

Throws:

GenericSignatureFormatError - if the generic signature does not conform to the format specified in the Virtual Machine specification, version 3.

Since:

1.5

getGenericExceptionTypes

public Type[] getGenericExceptionTypes()

Returns an array of Type objects that represents the exception types declared by this constructor, in declaration order. An array of size zero is returned if this constructor declares no exceptions.

Returns:

the exception types declared by this constructor.

Throws:

GenericSignatureFormatError - if the generic signature does not conform to the format specified in the Virtual Machine specification, version 3.

Since:

1.5

getGenericParameterTypes

public Type[] getGenericParameterTypes()

Returns an array of Type objects that represents the parameter list for this constructor, in declaration order. An array of size zero is returned if this constructor takes no parameters.

Returns:

a list of the types of the constructor's parameters

Throws:

GenericSignatureFormatError - if the generic signature does not conform to the format specified in the Virtual Machine specification, version 3.

Since:

1.5

getParameterAnnotations

public java.lang.annotation.Annotation[][] getParameterAnnotations()

Return an array of arrays representing the annotations on each of the constructor's parameters. The outer array is aligned against the parameters of the constructors and is thus equal in length to the number of parameters (thus having a length zero if there are none). Each array element in the outer array contains an inner array which holds the annotations. This array has a length of zero if the parameter has no annotations.

The returned annotations are serialized. Changing the annotations has no affect on the return value of future calls to this method.

Returns:

an array of arrays which represents the annotations used on the parameters of this constructor. The order of the array elements matches the declaration order of the parameters.

Since:

1.5

getAnnotation

public <T extends java.lang.annotation.Annotation> T getAnnotation(java.lang.Class<T> annotationClass)

Returns the element's annotation for the specified annotation type, or null if no such annotation exists.

Specified by:

getAnnotation in interface AnnotatedElement

Overrides:

getAnnotation in class AccessibleObject

Parameters:

annotationClass - the type of annotation to look for.

Returns:

this element's annotation for the specified type, or null if no such annotation exists.

Throws:

java.lang.NullPointerException - if the annotation class is null.

getDeclaredAnnotations

public java.lang.annotation.Annotation[] getDeclaredAnnotations()

Returns all annotations directly defined by the element. If there are no annotations directly associated with the element, then a zero-length array will be returned. The returned array may be modified by the client code, but this will have no effect on the annotation content of this class, and hence no effect on the return value of this method for future callers.

Specified by:

getDeclaredAnnotations in interface AnnotatedElement

Overrides:

getDeclaredAnnotations in class AccessibleObject

Returns:

the annotations directly defined by the element.

Since:

1.5