Java lang reflect method api

Package java.lang.reflect

Provides classes and interfaces for obtaining reflective information about classes and objects. Reflection allows programmatic access to information about the fields, methods, and constructors of loaded classes, and the use of reflected fields, methods, and constructors to operate on their underlying counterparts, within encapsulation and security restrictions.

Classes in this package, along with java.lang.Class accommodate applications such as debuggers, interpreters, object inspectors, class browsers, and services such as Object Serialization and JavaBeans that need access to either the public members of a target object (based on its runtime class) or the members declared by a given class.

AccessibleObject allows suppression of access checks if the necessary ReflectPermission is available.

Array provides static methods to dynamically create and access arrays.

Java programming language and JVM modeling in core reflection

The components of core reflection, which include types in this package as well as Class , Package , and Module , fundamentally present a JVM model of the entities in question rather than a Java programming language model. A Java compiler, such as javac , translates Java source code into executable output that can be run on a JVM, primarily class files. Compilers for source languages other than Java can and do target the JVM as well.

The translation process, including from Java language sources, to executable output for the JVM is not a one-to-one mapping. Structures present in the source language may have no representation in the output and structures not present in the source language may be present in the output. The latter are called synthetic structures. Synthetic structures can include methods, fields, parameters, classes and interfaces. One particular kind of synthetic method is a bridge method. It is possible a synthetic structure may not be marked as such. In particular, not all class file versions support marking a parameter as synthetic. A source language compiler generally has multiple ways to translate a source program into a class file representation. The translation may also depend on the version of the class file format being targeted as different class file versions have different capabilities and features. In some cases the modifiers present in the class file representation may differ from the modifiers on the originating element in the source language, including final on a parameter and protected , private , and static on classes and interfaces.

Besides differences in structural representation between the source language and the JVM representation, core reflection also exposes runtime specific information. For example, the class loaders and protection domains of a Class are runtime concepts without a direct analogue in source code.

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Java lang reflect method api

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.

Field Summary

Fields inherited from interface java.lang.reflect.Member

Method Summary

Returns an AnnotatedType object that represents the use of a type to specify the return type of the method/constructor represented by this Executable.

Returns this element’s annotation for the specified type if such an annotation is present, else null.

Returns the Class object representing the class or interface that declares the executable represented by this object.

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 Type objects that represent the exceptions declared to be thrown by this executable object.

Returns an array of Type objects that represent the formal parameter types, in declaration order, of the executable represented by this object.

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

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.

Returns the number of formal parameters (whether explicitly declared or implicitly declared or neither) for the executable represented by this object.

Returns an array of Class objects that represent the formal parameter types, in declaration order, of the executable represented by this object.

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

Returns an array of TypeVariable objects that represent the type variables declared by the generic declaration represented by this GenericDeclaration object, in declaration order.

Invokes the underlying method represented by this Method object, on the specified object with the specified parameters.

Returns true if this executable was declared to take a variable number of arguments; returns false otherwise.

Methods inherited from class java.lang.reflect.Executable

Methods inherited from class java.lang.reflect.AccessibleObject

Methods inherited from class java.lang.Object

Methods inherited from interface java.lang.reflect.AnnotatedElement

Method Detail

getDeclaringClass

Returns the Class object representing the class or interface that declares the executable represented by this object.

getName

getModifiers

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.

getReturnType

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

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.

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.

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.

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.

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.

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.

equals

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.

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.

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 .

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 .

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.

isBridge

isVarArgs

Returns true if this executable was declared to take a variable number of arguments; returns false otherwise.

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