JavaTM 2 Platform
Std. Ed. v1.3

Package java.lang

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


Interface Summary
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 is the standard wrapper for byte values.
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 defined by the Unicode 2.0 specification.
Class Instances of the class Class represent classes and interfaces in a running Java application.
ClassLoader The class ClassLoader is an abstract class.
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 InheritableThreadLocals 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 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 is the standard wrapper for short values.
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 ThreadLocal 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 primitive Java type 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 Thrown when an application tries to load in a class, but the currently executing method does not have access to the definition of the specified class, because the class is not public and in another package.
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 the charAt method in class String and by other String methods to indicate that an index is either negative or greater than or equal to 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.
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 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

Various constructors and methods in the java.lang and packages accept string arguments that specify the character encoding to be used when converting between raw eight-bit bytes and sixteen-bit Unicode characters. Such encodings are named by strings composed of the following characters: An encoding name must begin with either a letter or a digit. The empty string is not a legal encoding name.

An encoding may have more than one name. One of an encoding's names is considered to be its canonical name. The canonical name of an encoding is the name returned by the getEncoding methods of the InputStreamReader and OutputStreamWriter classes.

Encoding names generally follow the conventions documented in RFC2278: IANA Charset Registration Procedures. If an encoding listed in the IANA Charset Registry is supported by an implementation of the Java platform then one of its names must be the name listed in the registry. Many encodings are given more than one name in the registry, in which case the registry identifies one of the names as MIME-preferred. An implementation of the Java platform must support the MIME-preferred registry name for a supported encoding if there is one; for convenience it may additionally support other registry names. The IANA MIME-preferred name of an encoding, if there is one, is often, but not necessarily, its canonical name. Following IANA convention, the mapping from IANA registry names to encodings is not case-sensitive.

Every implementation of the Java platform is required to support the following character encodings. Consult the release documentation for your implementation to see if any other encodings are supported.

US-ASCII Seven-bit ASCII, a.k.a. ISO646-US, a.k.a. the Basic Latin block of the Unicode character set
ISO-8859-1   ISO Latin Alphabet No. 1, a.k.a. ISO-LATIN-1
UTF-8 Eight-bit Unicode Transformation Format
UTF-16BE Sixteen-bit Unicode Transformation Format, big-endian byte order
UTF-16LE Sixteen-bit Unicode Transformation Format, little-endian byte order
UTF-16 Sixteen-bit Unicode Transformation Format, byte order specified by a mandatory initial byte-order mark (either order accepted on input, big-endian used on output)
The various Unicode Transformation Formats are described in detail in The Unicode Standard and in the Unicode FAQ.

Every instance of the Java virtual machine has a default character encoding. The default encoding is determined during virtual-machine startup and typically depends upon the locale and encoding being used by the underlying operating system.


JavaTM 2 Platform
Std. Ed. v1.3

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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.

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