OpenJDK 1.23 · java.lang.reflect · APIdia, the JavaDoc alternative

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.

Interface Summary

Modifier and Type	Interface and Description
public interface	AnnotatedArrayType `AnnotatedArrayType` represents the potentially annotated use of an array type, whose component type may itself represent the annotated use of a type.
public interface	AnnotatedElement Represents an annotated construct of the program currently running in this VM.
public interface	AnnotatedParameterizedType `AnnotatedParameterizedType` represents the potentially annotated use of a parameterized type, whose type arguments may themselves represent annotated uses of types.
public interface	AnnotatedType `AnnotatedType` represents the potentially annotated use of a type in the program currently running in this VM.
public interface	AnnotatedTypeVariable `AnnotatedTypeVariable` represents the potentially annotated use of a type variable, whose declaration may have bounds which themselves represent annotated uses of types.
public interface	AnnotatedWildcardType `AnnotatedWildcardType` represents the potentially annotated use of a wildcard type argument, whose upper or lower bounds may themselves represent annotated uses of types.
public interface	GenericArrayType `GenericArrayType` represents an array type whose component type is either a parameterized type or a type variable.
public interface	GenericDeclaration A common interface for all entities that declare type variables.
public interface	InvocationHandler `InvocationHandler` is the interface implemented by the invocation handler of a proxy instance.
public interface	Member Member is an interface that reflects identifying information about a single member (a field or a method) or a constructor.
public interface	ParameterizedType ParameterizedType represents a parameterized type such as `Collection<String>`.
public interface	Type Type is the common superinterface for all types in the Java programming language.
public interface	TypeVariable< the type of generic declaration that declared the underlying type variable. D extends GenericDeclaration> TypeVariable is the common superinterface for type variables of kinds.
public interface	WildcardType WildcardType represents a wildcard type expression, such as `?`

Class Summary

Modifier and Type	Class and Description
public class	AccessibleObject The `AccessibleObject` class is the base class for `Field`, `Method`, and `Constructor` objects (known as reflected objects).
public class	Array The `Array` class provides static methods to dynamically create and access Java arrays.
public class	Constructor< the class in which the constructor is declared T> `Constructor` provides information about, and access to, a single constructor for a class.
public abstract class	Executable A shared superclass for the common functionality of `Method` and `Constructor`.
public class	Field A `Field` provides information about, and dynamic access to, a single field of a class or an interface.
public class	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.
public class	InaccessibleObjectException Thrown when Java language access checks cannot be suppressed.
public class	InvocationTargetException InvocationTargetException is a checked exception that wraps an exception thrown by an invoked method or constructor.
public class	MalformedParameterizedTypeException Thrown when a semantically malformed parameterized type is encountered by a reflective method that needs to instantiate it.
public class	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.
public class	Method A `Method` provides information about, and access to, a single method on a class or interface.
public class	Modifier The Modifier class provides `static` methods and constants to decode class and member access modifiers.
public class	Parameter Information about method parameters.
public class	Proxy `Proxy` provides static methods for creating objects that act like instances of interfaces but allow for customized method invocation.
pack-priv class	ProxyGenerator ProxyGenerator contains the code to generate a dynamic proxy class for the java.lang.reflect.Proxy API.
public class	RecordComponent A `RecordComponent` provides information about, and dynamic access to, a component of a record class.
pack-priv class	ReflectAccess Package-private class implementing the jdk.internal.access.JavaLangReflectAccess interface, allowing the java.lang package to instantiate objects in this package.
public class	ReflectPermission The Permission class for reflective operations.
public class	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.

Modifier and Type	Enum and Description
public enum	AccessFlag Represents a JVM access or module-related flag on a runtime member, such as a class, field, or method.
public enum	ClassFileFormatVersion Class file format versions of the Java virtual machine.

Package java.lang.reflect

Java programming language and JVM modeling in core reflection

Interface Summary

Class Summary

Enum Summary