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## Package java.lang

Provides classes that are fundamental to the design of the Java programming language.

See:
Description

Interface Summary
CharSequence | A `CharSequence` is a readable sequence of characters.
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.
Comparable | This interface imposes a total ordering on the objects of each class that implements it.
Runnable | The `Runnable` interface should be implemented by any class whose instances are intended to be executed by a thread.

Class Summary
Boolean | The Boolean class wraps a value of the primitive type `boolean` in an object.
Byte | The `Byte` class wraps a value of primitive type `byte` in an object.
Character | The `Character` class wraps a value of the primitive type `char` in an object.
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.
Class | Instances of the class `Class` represent classes and interfaces in a running Java application.
ClassLoader | A class loader is an object that is responsible for loading classes.
Compiler | The `Compiler` class is provided to support Java-to-native-code compilers and related services.
Double | The `Double` class wraps a value of the primitive type `double` in an object.
Float | The `Float` class wraps a value of primitive type `float` in an object.
InheritableThreadLocal | 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.
Integer | The `Integer` class wraps a value of the primitive type `int` in an object.
Long | The `Long` class wraps a value of the primitive type `long` in an object.
Math | The class `Math` contains methods for performing basic numeric operations such as the elementary exponential, logarithm, square root, and trigonometric functions.
Number | The abstract class `Number` is the superclass of classes `BigDecimal`, `BigInteger`, `Byte`, `Double`, `Float`, `Integer`, `Long`, and `Short`.
Object | Class `Object` is the root of the class hierarchy.
Package | `Package` objects contain version information about the implementation and specification of a Java package.
Process | The `Runtime.exec` methods create a native process and return an instance of a subclass of `Process` that can be used to control the process and obtain information about it.
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.
RuntimePermission | This class is for runtime permissions.
SecurityManager | The security manager is a class that allows applications to implement a security policy.
Short | The `Short` class wraps a value of primitive type `short` in an object.
StackTraceElement | An element in a stack trace, as returned by `Throwable.getStackTrace()`.
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 string buffer implements a mutable sequence of characters.
System | The `System` class contains several useful class fields and methods.
Thread | A thread is a thread of execution in a program.
ThreadGroup | A thread group represents a set of threads.
ThreadLocal | This class provides thread-local variables.
Throwable | The `Throwable` class is the superclass of all errors and exceptions in the Java language.
Void | The Void class is an uninstantiable placeholder class to hold a reference to the Class object representing the Java keyword void.

Exception Summary
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.
ClassCastException | Thrown to indicate that the code has attempted to cast an object to a subclass of which it is not an instance.
ClassNotFoundException | Thrown when an application tries to load in a class through its string name using: The `forName` method in class `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.
Exception | The class `Exception` and its subclasses are a form of `Throwable` that indicates conditions that a reasonable application might want to catch.
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.
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.
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.
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 because it is an interface or is an abstract class.
InterruptedException | Thrown when a thread is waiting, sleeping, or otherwise paused for a long time and another thread interrupts it using the `interrupt` method in class `Thread`.
NegativeArraySizeException | Thrown if an application tries to create an array with negative size.
NoSuchFieldException | Signals that the class doesn't have a field of a specified name.
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.
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.
RuntimeException | `RuntimeException` is the superclass of those exceptions that can be thrown during the normal operation of the Java Virtual Machine.
SecurityException | Thrown by the security manager to indicate a security violation.
StringIndexOutOfBoundsException | Thrown by `String` methods to indicate that an index is either negative or greater than the size of the string.
UnsupportedOperationException | Thrown to indicate that the requested operation is not supported.

Error Summary
AbstractMethodError | Thrown when an application tries to call an abstract method.
AssertionError | Thrown to indicate that an assertion has failed.
ClassCircularityError | Thrown when a circularity has been detected while initializing a class.
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.
Error | An `Error` is a subclass of `Throwable` that indicates serious problems that a reasonable application should not try to catch.
ExceptionInInitializerError | Signals that an unexpected exception has occurred in a static initializer.
IllegalAccessError | Thrown if an application attempts to access or modify a field, or to call a method that it does not have access to.
IncompatibleClassChangeError | Thrown when an incompatible class change has occurred to some class definition.
InstantiationError | Thrown when an application tries to use the Java `new` construct to instantiate an abstract class or an interface.
InternalError | Thrown to indicate some unexpected internal error has occurred in the Java Virtual Machine.
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.
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.
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.
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.
StackOverflowError | Thrown when a stack overflow occurs because an application recurses too deeply.
ThreadDeath | An instance of `ThreadDeath` is thrown in the victim thread when the `stop` method with zero arguments in class `Thread` is called.
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.
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.

## Package java.lang Description

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`, `Character`, `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. These classes also provide a number of methods for converting among primitive values, as well as supporting such standard methods as equals and hashCode. The `Void` class is a non-instantiable class that holds a reference to a `Class` object represening the primitive type void.

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

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

Class `Throwable` encompasses objects that may be thrown by the throw statement (§14.16). Subclasses of `Throwable` represent errors and exceptions.

## Package Specification

### 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:
  JDK1.0

Overview | Package | Class | Use | Tree | Deprecated | Index | Help
| JavaTM 2 Platform Std. Ed. v1.4.1
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For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

Copyright 2002 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms.