# Package java.lang

package java.lang
Provides classes that are fundamental to the design of the Java programming language. The most important classes are `Object`, which is the root of the class hierarchy, and `Class`, instances of which represent classes at run time.

Frequently it is necessary to represent a value of primitive type as if it were an object.The wrapper classes `Boolean`, `Byte`, `Character`, `Short`, `Integer`, `Long`, `Float`, and `Double` serve this purpose. An object of type `Double`, for example, contains a field whose type is `double`, representing that value in such a way that a reference to it can be stored in a variable of reference type. As discussed in The Java Language Specification, the wrapper classes are involved in boxing (JLS 5.1.7) and unboxing (JLS 5.1.8) conversions. These classes provide a number of methods for converting among primitive values, as well as methods supporting such standard functionality as `equals` and `hashCode`. The `Void` class is a non-instantiable class that holds a reference to a `Class` object representing the type `void`.

The class `Math` provides commonly used mathematical functions such as sine, cosine, and square root. The classes `String`, `StringBuffer`, and `StringBuilder` similarly provide commonly used operations on character strings.

Classes `ClassLoader`, `Process`, `ProcessBuilder`, `Runtime`, and `System` provide "system operations" that manage the dynamic loading of classes, creation of external processes, and host environment inquiries such as the time of day.

Class `Throwable` encompasses objects that may be thrown by the `throw` statement. Subclasses of `Throwable` represent errors and exceptions.

## Character Encodings

The specification of the `java.nio.charset.Charset` class describes the naming conventions for character encodings as well as the set of standard encodings that must be supported by every implementation of the Java platform.

Since:
  1.0

Related Packages
Module
Package
Description
java.base
java.lang.annotation
Provides library support for the Java programming language annotation facility.
java.base
java.lang.classfile
Provides classfile parsing, generation, and transformation library.
java.base
java.lang.constant
Classes and interfaces to represent nominal descriptors for run-time entities such as classes or method handles, and classfile entities such as constant pool entries or `invokedynamic` call sites.
java.base
java.lang.foreign
Provides low-level access to memory and functions outside the Java runtime.
java.instrument
java.lang.instrument
Provides services that allow Java programming language agents to instrument programs running on the Java Virtual Machine (JVM).
java.base
java.lang.invoke
The `java.lang.invoke` package provides low-level primitives for interacting with the Java Virtual Machine.
java.management
java.lang.management
Provides the management interfaces for monitoring and management of the Java virtual machine and other components in the Java runtime.
java.base
java.lang.module
Classes to support module descriptors and creating configurations of modules by means of resolution and service binding.
java.base
java.lang.ref
Provides reference-object classes, which support a limited degree of interaction with the garbage collector.
java.base
java.lang.reflect
Provides classes and interfaces for obtaining reflective information about classes and objects.
java.base
java.lang.runtime
The `java.lang.runtime` package provides low-level runtime support for the Java language.
Class
Description
AbstractMethodError
Thrown when an application tries to call an abstract method.
Appendable
An object to which `char` sequences and values can be appended.
ArithmeticException
Thrown when an exceptional arithmetic condition has occurred.
ArrayIndexOutOfBoundsException
Thrown to indicate that an array has been accessed with an illegal index.
ArrayStoreException
Thrown to indicate that an attempt has been made to store the wrong type of object into an array of objects.
AssertionError
Thrown to indicate that an assertion has failed.
AutoCloseable
An object that may hold resources (such as file or socket handles) until it is closed.
Boolean
The `Boolean` class is the wrapper class for values of the primitive type `boolean`.
BootstrapMethodError
Thrown to indicate that an `invokedynamic` instruction or a dynamic constant failed to resolve its bootstrap method and arguments, or for `invokedynamic` instruction the bootstrap method has failed to provide a call site with a target of the correct method type, or for a dynamic constant the bootstrap method has failed to provide a constant value of the required type.
Byte
The `Byte` class is the wrapper class for values of the primitive type `byte`.
Character
The `Character` class is the wrapper class for values of the primitive type `char`.
Character.Subset
Instances of this class represent particular subsets of the Unicode character set.
Character.UnicodeBlock
A family of character subsets representing the character blocks in the Unicode specification.
Character.UnicodeScript
A family of character subsets representing the character scripts defined in the Unicode Standard Annex #24: Script Names.
CharSequence
A `CharSequence` is a readable sequence of `char` values.
Class<T>
Instances of the class `Class` represent classes and interfaces in a running Java application.
ClassCastException
Thrown to indicate that the code has attempted to cast an object to a subclass of which it is not an instance.
ClassCircularityError
Thrown when the Java Virtual Machine detects a circularity in the superclass hierarchy of a class being loaded.
ClassFormatError
Thrown when the Java Virtual Machine attempts to read a class file and determines that the file is malformed or otherwise cannot be interpreted as a class file.
ClassLoader
A class loader is an object that is responsible for loading classes.
ClassNotFoundException
Thrown when an application tries to load in a class through its string name using: The `forName` method in class `Class`.
ClassValue<T>
Lazily associate a computed value with (potentially) every type.
Cloneable
A class implements the `Cloneable` interface to indicate to the `Object.clone()` method that it is legal for that method to make a field-for-field copy of instances of that class.
CloneNotSupportedException
Thrown to indicate that the `clone` method in class `Object` has been called to clone an object, but that the object's class does not implement the `Cloneable` interface.
Comparable<T>
This interface imposes a total ordering on the objects of each class that implements it.
Deprecated
A program element annotated `@Deprecated` is one that programmers are discouraged from using.
Double
The `Double` class is the wrapper class for values of the primitive type `double`.
Enum<E extends Enum<E>>
This is the common base class of all Java language enumeration classes.
Enum.EnumDesc<E extends Enum<E>>
A nominal descriptor for an `enum` constant.
EnumConstantNotPresentException
Thrown when an application tries to access an enum constant by name and the enum type contains no constant with the specified name.
Error
An `Error` is a subclass of `Throwable` that indicates serious problems that a reasonable application should not try to catch.
Exception
The class `Exception` and its subclasses are a form of `Throwable` that indicates conditions that a reasonable application might want to catch.
ExceptionInInitializerError
Signals that an unexpected exception has occurred in a static initializer.
Float
The `Float` class is the wrapper class for values of the primitive type `float`.
FunctionalInterface
An informative annotation type used to indicate that an interface type declaration is intended to be a functional interface as defined by the Java Language Specification.
IllegalAccessError
Thrown if an application attempts to access or modify a field, or to call a method that it does not have access to.
IllegalAccessException
An IllegalAccessException is thrown when an application tries to reflectively create an instance (other than an array), set or get a field, or invoke a method, but the currently executing method does not have access to the definition of the specified class, field, method or constructor.
IllegalArgumentException
Thrown to indicate that a method has been passed an illegal or inappropriate argument.
IllegalCallerException
Thrown to indicate that a method has been called by an inappropriate caller.
IllegalMonitorStateException
Thrown to indicate that a thread has attempted to wait on an object's monitor or to notify other threads waiting on an object's monitor without owning the specified monitor.
IllegalStateException
Signals that a method has been invoked at an illegal or inappropriate time.
IllegalThreadStateException
Thrown to indicate that a thread is not in an appropriate state for the requested operation.
IncompatibleClassChangeError
Thrown when an incompatible class change has occurred to some class definition.
IndexOutOfBoundsException
Thrown to indicate that an index of some sort (such as to an array, to a string, or to a vector) is out of range.
InheritableThreadLocal<T>
This class extends `ThreadLocal` to provide inheritance of values from parent thread to child thread: when a child thread is created, the child receives initial values for all inheritable thread-local variables for which the parent has values.
InstantiationError
Thrown when an application tries to use the Java `new` construct to instantiate an abstract class or an interface.
InstantiationException
Thrown when an application tries to create an instance of a class using the `newInstance` method in class `Class`, but the specified class object cannot be instantiated.
Integer
The `Integer` class is the wrapper class for values of the primitive type `int`.
InternalError
Thrown to indicate some unexpected internal error has occurred in the Java Virtual Machine.
InterruptedException
Thrown when a thread is waiting, sleeping, or otherwise occupied, and the thread is interrupted, either before or during the activity.
Iterable<T>
Implementing this interface allows an object to be the target of the enhanced `for` statement (sometimes called the "for-each loop" statement).
LayerInstantiationException
Thrown when creating a module layer fails.
LinkageError
Subclasses of `LinkageError` indicate that a class has some dependency on another class; however, the latter class has incompatibly changed after the compilation of the former class.
Long
The `Long` class is the wrapper class for values of the primitive type `long`.
MatchException
Thrown to indicate an unexpected failure in pattern matching.
Math
The class `Math` contains methods for performing basic numeric operations such as the elementary exponential, logarithm, square root, and trigonometric functions.
Module
Represents a run-time module, either `named` or unnamed.
ModuleLayer
A layer of modules in the Java virtual machine.
ModuleLayer.Controller
Controls a module layer.
NegativeArraySizeException
Thrown if an application tries to create an array with negative size.
NoClassDefFoundError
Thrown if the Java Virtual Machine or a `ClassLoader` instance tries to load in the definition of a class (as part of a normal method call or as part of creating a new instance using the `new` expression) and no definition of the class could be found.
NoSuchFieldError
Thrown if an application tries to access or modify a specified field of an object, and that object no longer has that field.
NoSuchFieldException
Signals that the class doesn't have a field of a specified name.
NoSuchMethodError
Thrown if an application tries to call a specified method of a class (either static or instance), and that class no longer has a definition of that method.
NoSuchMethodException
Thrown when a particular method cannot be found.
NullPointerException
Thrown when an application attempts to use `null` in a case where an object is required.
Number
The abstract class `Number` is the superclass of platform classes representing numeric values that are convertible to the primitive types `byte`, `double`, `float`, `int`, `long`, and `short`.
NumberFormatException
Thrown to indicate that the application has attempted to convert a string to one of the numeric types, but that the string does not have the appropriate format.
Object
Class `Object` is the root of the class hierarchy.
OutOfMemoryError
Thrown when the Java Virtual Machine cannot allocate an object because it is out of memory, and no more memory could be made available by the garbage collector.
Override
Indicates that a method declaration is intended to override a method declaration in a supertype.
Package
Represents metadata about a run-time package associated with a class loader.
Process
`Process` provides control of native processes started by ProcessBuilder.start and Runtime.exec.
ProcessBuilder
This class is used to create operating system processes.
ProcessBuilder.Redirect
Represents a source of subprocess input or a destination of subprocess output.
ProcessBuilder.Redirect.Type
The type of a `ProcessBuilder.Redirect`.
ProcessHandle
ProcessHandle identifies and provides control of native processes.
ProcessHandle.Info
Information snapshot about the process.
Readable
A `Readable` is a source of characters.
Record
This is the common base class of all Java language record classes.
ReflectiveOperationException
Common superclass of exceptions thrown by reflective operations in core reflection.
Runnable
Represents an operation that does not return a result.
Runtime
Every Java application has a single instance of class `Runtime` that allows the application to interface with the environment in which the application is running.
Runtime.Version
A representation of a version string for an implementation of the Java SE Platform.
RuntimeException
`RuntimeException` is the superclass of those exceptions that can be thrown during the normal operation of the Java Virtual Machine.
RuntimePermission
This class is for runtime permissions.
SafeVarargs
A programmer assertion that the body of the annotated method or constructor does not perform potentially unsafe operations on its varargs parameter.
ScopedValuePREVIEW<T>
Preview.
A value that may be safely and efficiently shared to methods without using method parameters.
ScopedValue.CallableOpPREVIEW<T, X extends Throwable>
Preview.
An operation that returns a result and may throw an exception.
ScopedValue.CarrierPREVIEW
Preview.
A mapping of scoped values, as keys, to values.
SecurityException
Thrown to indicate a security violation.
SecurityManager
Deprecated, for removal: This API element is subject to removal in a future version.
There is no replacement for this class.
Short
The `Short` class is the wrapper class for values of the primitive type `short`.
StackOverflowError
Thrown when a stack overflow occurs because an application recurses too deeply.
StackTraceElement
An element in a stack trace, as returned by `Throwable.getStackTrace()`.
StackWalker
A stack walker.
StackWalker.Option
Stack walker option to configure the stack frame information obtained by a `StackWalker`.
StackWalker.StackFrame
A `StackFrame` object represents a method invocation returned by `StackWalker`.
StrictMath
The class `StrictMath` contains methods for performing basic numeric operations such as the elementary exponential, logarithm, square root, and trigonometric functions.
String
The `String` class represents character strings.
StringBuffer
A thread-safe, mutable sequence of characters.
StringBuilder
A mutable sequence of characters.
StringIndexOutOfBoundsException
Thrown by `String` methods to indicate that an index is either negative or greater than the size of the string.
SuppressWarnings
Indicates the warnings to be suppressed at compile time in the annotated element, and in all elements contained in the annotated element.
System
The `System` class contains several useful class fields and methods.
System.Logger
`System.Logger` instances log messages that will be routed to the underlying logging framework the `LoggerFinder` uses.
System.Logger.Level
System loggers levels.
System.LoggerFinder
The `LoggerFinder` service is responsible for creating, managing, and configuring loggers to the underlying framework it uses.
Thread
A thread is a thread of execution in a program.
Thread.Builder
A builder for `Thread` and `ThreadFactory` objects.
Thread.Builder.OfPlatform
A builder for creating a platform `Thread` or `ThreadFactory` that creates platform threads.
Thread.Builder.OfVirtual
A builder for creating a virtual `Thread` or `ThreadFactory` that creates virtual threads.
Thread.State
A thread state.
Thread.UncaughtExceptionHandler
Interface for handlers invoked when a `Thread` abruptly terminates due to an uncaught exception.
ThreadDeath
Deprecated, for removal: This API element is subject to removal in a future version.
`Thread.stop()` was originally specified to "stop" a victim thread by causing the victim thread to throw a `ThreadDeath`.
ThreadGroup
A thread group represents a set of threads.
ThreadLocal<T>
This class provides thread-local variables.
Throwable
The `Throwable` class is the superclass of all errors and exceptions in the Java language.
TypeNotPresentException
Thrown when an application tries to access a type using a string representing the type's name, but no definition for the type with the specified name can be found.
UnknownError
Thrown when an unknown but serious exception has occurred in the Java Virtual Machine.
UnsatisfiedLinkError
Thrown if the Java Virtual Machine cannot find an appropriate native-language definition of a method declared `native`.
UnsupportedClassVersionError
Thrown when the Java Virtual Machine attempts to read a class file and determines that the major and minor version numbers in the file are not supported.
UnsupportedOperationException
Thrown to indicate that the requested operation is not supported.
VerifyError
Thrown when the "verifier" detects that a class file, though well formed, contains some sort of internal inconsistency or security problem.
VirtualMachineError
Thrown to indicate that the Java Virtual Machine is broken or has run out of resources necessary for it to continue operating.
Void
The `Void` class is an uninstantiable placeholder class to hold a reference to the `Class` object representing the Java keyword void.
WrongThreadException
Thrown to indicate that a method has been called on the wrong thread.