Module java.base

Package java.lang.reflect

packagejava.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 withjava.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 necessaryReflectPermission 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 asClass,Package, andModule, fundamentally present a JVM model of the entities in question rather than a Java programming language model. A Java compiler, such asjavac, translates Java source code into executable output that can be run on a JVM, primarilyclass 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 structuresnot present in the source language may be present in the output. The latter are calledsynthetic structures. Synthetic structures can includemethods,fields,parameters,classes and interfaces. One particular kind of synthetic method is abridge method. It is possible a synthetic structure may not be marked as such. In particular, not allclass file versions support marking a parameter as synthetic. A source language compiler generally has multiple ways to translate a source program into aclass file representation. The translation may also depend on the version of theclass file format being targeted as different class file versions have different capabilities and features. In some cases the modifiers present in theclass file representation may differ from the modifiers on the originating element in the source language, includingfinal on aparameter andprotected,private, andstatic onclasses and interfaces.

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

SeeJava Language Specification:
13.1 The Form of a Binary
SeeJava 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
    Provides classes that are fundamental to the design of the Java programming language.
  • Class
    Description
    TheAccessibleObject class is the base class forField,Method, andConstructor objects (known asreflected objects).
    AnnotatedArrayType represents the potentially annotated use of an array type, whose component type may itself represent the annotated use of a type.
    Represents an annotated construct of the program currently running in this VM.
    AnnotatedParameterizedType represents the potentially annotated use of a parameterized type, whose type arguments may themselves represent annotated uses of types.
    AnnotatedType represents the potentially annotated use of a type in the program currently running in this VM.
    AnnotatedTypeVariable represents the potentially annotated use of a type variable, whose declaration may have bounds which themselves represent annotated uses of types.
    AnnotatedWildcardType represents the potentially annotated use of a wildcard type argument, whose upper or lower bounds may themselves represent annotated uses of types.
    TheArray class provides static methods to dynamically create and access Java arrays.
    Constructor provides information about, and access to, a single constructor for a class.
    A shared superclass for the common functionality ofMethod andConstructor.
    AField provides information about, and dynamic access to, a single field of a class or an interface.
    GenericArrayType represents an array type whose component type is either a parameterized type or a type variable.
    A common interface for all entities that declare type variables.
    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.
    Thrown when Java language access checks cannot be suppressed.
    InvocationHandler is the interface implemented by theinvocation handler of a proxy instance.
    InvocationTargetException is a checked exception that wraps an exception thrown by an invoked method or constructor.
    Thrown when a semantically malformed parameterized type is encountered by a reflective method that needs to instantiate it.
    Thrown whenthe java.lang.reflect package attempts to read method parameters from a class file and determines that one or more parameters are malformed.
    Member is an interface that reflects identifying information about a single member (a field or a method) or a constructor.
    AMethod provides information about, and access to, a single method on a class or interface.
    The Modifier class providesstatic methods and constants to decode class and member access modifiers.
    Information about method parameters.
    ParameterizedType represents a parameterized type such asCollection<String>.
    Proxy provides static methods for creating objects that act like instances of interfaces but allow for customized method invocation.
    ARecordComponent provides information about, and dynamic access to, a component of a record class.
    The Permission class for reflective operations.
    Type is the common superinterface for all types in the Java programming language.
    TypeVariable is the common superinterface for type variables of kinds.
    Thrown by a method invocation on a proxy instance if its invocation handler'sinvoke method throws a checked exception (aThrowable that is not assignable toRuntimeException orError) that is not assignable to any of the exception types declared in thethrows clause of the method that was invoked on the proxy instance and dispatched to the invocation handler.
    WildcardType represents a wildcard type expression, such as?,? extends Number, or? super Integer.