Java Platform, Standard Edition

The java.lang contains fundamental classes and interfaces that are closely tied to the language and system at runtime. This includes the root classes that form the hierarchy of classes, types that are tied to the language definition, the main exceptions , mathematical functions, multithreading support classes, security functions, as well as classes that provide information about the operating system on which the program is running.

The main classes in java.lang :

• Object - this class is the root of the class hierarchy in Java;
• Enum - the base class for the enumerated type (from version J2SE 5.0);
• Class - the class is the main one in the Java introspection subsystem;
• ClassLoader is an abstract class that defines how classes are loaded. Your application can create subclasses that extend ClassLoader by implementing its methods. This allows classes to be loaded in other ways than the one that normally loads in the Java runtime system. However, usually you should not do this;
• Throwable - the class is the base for the hierarchy of exception classes;
• Error , Exception , RuntimeException - base classes for each subtype of exceptions;
• Thread - a class containing operations on threads of execution;
• String - a class for representing strings and their values;
• StringBuffer and StringBuilder - classes for working with strings ( StringBuilder since version J2SE 5.0);
• Comparable - an interface to support generalized comparison and ordering of objects (since J2SE 1.2);
• Iterable - an interface to support the improved for loop (since J2SE version 5.0);
• Process , Runtime , SecurityManager , System - perform "system operations". They manage the dynamic loading of classes, the creation of external processes , obtaining information about the environment (for example, time of day), and monitor the implementation of security policies ;
• Math and StrictMath - contain basic mathematical functions, such as calculating the sine , cosine and square root ( StrictMath from version J2SE 1.3);
• Wrapping classes over primitive types that turn them into objects;
• Exclusion classes for basic language and runtime exceptions.

All classes from the java.lang automatically included in each source program file. Explicit connection is not required.

java.lang.annotation

This package defines the Annotation interface, as well as the ElementType and RetentionPolicy enumerations.

java.lang.instrument

The package defines the tools that can be used to add tools for various aspects of program execution. It defines the Instrumentation and ClassFileTransformer interfaces, as well as the ClassDefinition class.

java.lang.management

The package provides support for managing the Java Virtual Machine and runtime. Using the tools of the package, you can view and manage various aspects of program execution.

java.lang.ref

Provides the ability to interact with the garbage collector , so the program can be warned about changing the number of references to the object or about the actions performed by the garbage collector on the object.

java.lang.reflect

The java.lang.reflect provides a reflection mechanism — the ability of software to introspect (that is, to obtain information about the classes available in the system, their methods, fields and relationships). Reflection is an important feature required when using components called JavaBeans .

It contains classes for providing file input-output of information, several classes of input-output abstraction, as well as a set of classes for processing input information: token allocation, etc.

Contains classes for computing large integers ( BigInteger class) and arbitrary decimal fractions ( BigDecimal class). It also contains methods for performing operations on numbers: obtaining their absolute value, etc.

Contains classes that allow the application to work with the network, providing abstractions for network addresses, connections, socket implementations, etc.

A set of classes and utilities that allow you to organize work with various data formats, apply existing ones, or create your own formatting templates (for example, the format for displaying a date or a floating-point number).

Helper classes and interfaces. Very convenient and used in almost every program.

To work in the browser.

Contains classes for writing user interfaces, working with images, and drawing.

Java Database Connectivity

It contains a set of graphical components that allow you to create graphical interfaces that work as equally as possible on all platforms.

• http://java.sun.com/docs/books/tutorial/getStarted/index.html
• https://web.archive.org/web/20070524162037/http://doc.java.sun.com/DocWeb/

• Herbert Schildt . Complete Java SE 6 Reference = Java: The Complete Reference. - 7th ed. - M .: "Williams" , 2007. - S. 1040. - ISBN 0-07-226385-7 .