Module java.base

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.

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.

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
    Provides classes that are fundamental to the design of the Java programming language.
  • Interface Summary
    Interface
    Description
    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.
    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.
    InvocationHandler is the interface implemented by the invocation handler of a proxy instance.
    Member is an interface that reflects identifying information about a single member (a field or a method) or a constructor.
    ParameterizedType represents a parameterized type such as Collection<String>.
    Type is the common superinterface for all types in the Java programming language.
    TypeVariable is the common superinterface for type variables of kinds.
    WildcardType represents a wildcard type expression, such as ?, ? extends Number, or ? super Integer.
  • Class Summary
    Class
    Description
    The AccessibleObject class is the base class for Field, Method, and Constructor objects (known as reflected objects).
    The Array 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 of Method and Constructor.
    A Field provides information about, and dynamic access to, a single field of a class or an interface.
    A Method provides information about, and access to, a single method on a class or interface.
    The Modifier class provides static methods and constants to decode class and member access modifiers.
    Information about method parameters.
    Proxy provides static methods for creating objects that act like instances of interfaces but allow for customized method invocation.
    A RecordComponent provides information about, and dynamic access to, a component of a record class.
    The Permission class for reflective operations.
  • Exception Summary
    Exception
    Description
    Thrown when Java language access checks cannot be suppressed.
    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 when the java.lang.reflect package attempts to read method parameters from a class file and determines that one or more parameters are malformed.
    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.
  • Error Summary
    Error
    Description
    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.