java.lang.reflect (Java SE 26 & JDK 26)
Description: declaration: module: java.base, package: java.lang.reflect
Keywords: java.lang.reflect package

# Package java.lang.reflect

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.

`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.

See Java Language Specification:
  13.1 The Form of a Binary
See Java Virtual Machine Specification:
  1.2 The Java Virtual Machine
  4.7.8 The Synthetic Attribute
  5.3.1 Loading Using the Bootstrap Class Loader
  5.3.2 Loading Using a User-defined Class Loader
Since:
  1.1

- Related Packages
  Package
  Description
  java.lang
  Provides classes that are fundamental to the design of the Java programming language.
- Class
  Description
  AccessFlag
  Represents a JVM access or module-related flag on a runtime member, such as a class, field, or method.
  AccessFlag.Location
  A location within a `class` file where flags can be applied.
  AccessibleObject
  The `AccessibleObject` class is the base class for `Field`, `Method`, and `Constructor` objects (known as reflected objects).
  AnnotatedArrayType
  `AnnotatedArrayType` represents the potentially annotated use of an array type, whose component type may itself represent the annotated use of a type.
  AnnotatedElement
  Represents an annotated construct of the program currently running in this VM.
  AnnotatedParameterizedType
  `AnnotatedParameterizedType` represents the potentially annotated use of a parameterized type, whose type arguments may themselves represent annotated uses of types.
  AnnotatedType
  `AnnotatedType` represents the potentially annotated use of a type in the program currently running in this VM.
  AnnotatedTypeVariable
  `AnnotatedTypeVariable` represents the potentially annotated use of a type variable, whose declaration may have bounds which themselves represent annotated uses of types.
  AnnotatedWildcardType
  `AnnotatedWildcardType` represents the potentially annotated use of a wildcard type argument, whose upper or lower bounds may themselves represent annotated uses of types.
  Array
  The `Array` class provides static methods to dynamically create and access Java arrays.
  ClassFileFormatVersion
  Class file format versions of the Java virtual machine.
  Constructor<T>
  `Constructor` provides information about, and access to, a single constructor for a class.
  Executable
  A shared superclass for the common functionality of `Method` and `Constructor`.
  Field
  A `Field` provides information about, and dynamic access to, a single field of a class or an interface.
  GenericArrayType
  `GenericArrayType` represents an array type whose component type is either a parameterized type or a type variable.
  GenericDeclaration
  A common interface for all entities that declare type variables.
  GenericSignatureFormatError
  Thrown when a syntactically malformed signature attribute is encountered by a reflective method that needs to interpret the generic signature information for a class or interface, method or constructor.
  InaccessibleObjectException
  Thrown when Java language access checks cannot be suppressed.
  InvocationHandler
  `InvocationHandler` is the interface implemented by the invocation handler of a proxy instance.
  InvocationTargetException
  InvocationTargetException is a checked exception that wraps an exception thrown by an invoked method or constructor.
  MalformedParameterizedTypeException
  Thrown when a semantically malformed parameterized type is encountered by a reflective method that needs to instantiate it.
  MalformedParametersException
  Thrown when `the java.lang.reflect package` attempts to read method parameters from a class file and determines that one or more parameters are malformed.
  Member
  Member is an interface that reflects identifying information about a single member (a field or a method) or a constructor.
  Method
  A `Method` provides information about, and access to, a single method on a class or interface.
  Modifier
  The Modifier class provides `static` methods and constants to decode class and member access modifiers.
  Parameter
  Information about method parameters.
  ParameterizedType
  ParameterizedType represents a parameterized type such as `Collection<String>`.
  Proxy
  `Proxy` provides static methods for creating objects that act like instances of interfaces but allow for customized method invocation.
  RecordComponent
  A `RecordComponent` provides information about, and dynamic access to, a component of a record class.
  ReflectPermission
  Deprecated, for removal: This API element is subject to removal in a future version.
  This permission cannot be used for controlling access to resources as the Security Manager is no longer supported.
  Type
  Type is the common superinterface for all types in the Java programming language.
  TypeVariable<D extends GenericDeclaration>
  TypeVariable is the common superinterface for type variables of kinds.
  UndeclaredThrowableException
  Thrown by a method invocation on a proxy instance if its invocation handler's `invoke` method throws a checked exception (a `Throwable` that is not assignable to `RuntimeException` or `Error`) that is not assignable to any of the exception types declared in the `throws` clause of the method that was invoked on the proxy instance and dispatched to the invocation handler.
  WildcardType
  WildcardType represents a wildcard type expression, such as `?`, `? extends Number`, or `? super Integer`.