java.lang

  • The java.lang package provides essential classes and interfaces for the Java programming language, including core classes like Object, String, and Math, and interfaces like Runnable and Comparable.

  • This package also defines annotations used for code clarity and compiler instructions, such as @Deprecated, @Override, and @SuppressWarnings.

  • It includes a hierarchy of classes for exception handling, including Throwable, Error, and Exception, as well as specific exception types like ArithmeticException and NullPointerException.

  • The java.lang package is fundamental to Java development and provides the building blocks for basic functionalities and runtime behavior.

  • Developers utilize this package extensively for object manipulation, string processing, mathematical calculations, and handling runtime errors.
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 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, 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. 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.

Annotations

Deprecated A program element annotated @Deprecated is one that programmers are discouraged from using, typically because it is dangerous, or because a better alternative exists. 
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. 
Override Indicates that a method declaration is intended to override a method declaration in a supertype. 
SafeVarargs A programmer assertion that the body of the annotated method or constructor does not perform potentially unsafe operations on its varargs parameter. 
SuppressWarnings Indicates that the named compiler warnings should be suppressed in the annotated element (and in all program elements contained in the annotated element). 

Interfaces

Appendable An object to which char sequences and values can be appended. 
AutoCloseable An object that may hold resources (such as file or socket handles) until it is closed. 
CharSequence A CharSequence is a readable sequence of char values. 
Cloneable This (empty) interface must be implemented by all classes that wish to support cloning. 
Comparable<T> This interface imposes a total ordering on the objects of each class that implements it. 
Iterable<T> Implementing this interface allows an object to be the target of the "for-each loop" statement. 
Readable A Readable is a source of characters. 
Runnable The Runnable interface should be implemented by any class whose instances are intended to be executed by a thread. 

Classes

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<T> 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. 
Double The Double class wraps a value of the primitive type double in an object. 
Enum<E extends Enum<E>> This is the common base class of all Java language enumeration types. 
Float The Float class wraps a value of primitive type float in an object. 
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. 
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 platform classes representing numeric values that are convertible to the primitive types byte, double, float, int, long, and short. 
Object The root class of the Java class hierarchy. 
Package Package objects contain version information about the implementation and specification of a Java package. 
RuntimePermission Legacy security code; do not use. 
SecurityManager Legacy security code; do not use. 
Short The Short class wraps a value of primitive type short in an object. 
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. 
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. 
Void The Void class is an uninstantiable placeholder class to hold a reference to the Class object representing the Java keyword void. 

Enums

Character.UnicodeScript A family of character subsets representing the character scripts defined in the Unicode Standard Annex #24: Script Names. 

Exceptions

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. 
EnumConstantNotPresentException Thrown when an application tries to access an enum constant by name and the enum type contains no constant with the specified name. 
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. 
InterruptedException Thrown when a thread is waiting, sleeping, or otherwise occupied, and the thread is interrupted, either before or during the activity. 
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. 
ReflectiveOperationException Common superclass of exceptions thrown by reflective operations in core reflection. 
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. 
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. 
UnsupportedOperationException Thrown to indicate that the requested operation is not supported. 

Errors

AbstractMethodError Thrown when an application tries to call an abstract method. 
AssertionError Thrown to indicate that an assertion has failed. 
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. 
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 (deprecated) Thread.stop() method is invoked. 
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. 
VirtualMachineError Thrown to indicate that the Java Virtual Machine is broken or has run out of resources necessary for it to continue operating.