12 Introduction to Java API

1
12 Introduction to Java API
2
Contents

• Java API Specifications
• java.lang package
• Object class
• Class class
• System class
• String and StringBuffer classes
• Math class
• java.util package

3
Objectives

• Navigate the Java API Specifications
• Describe the java.lang package
• Explore fundamental classes in java.lang package
  
• Object
• Class
• System
• String
• StringBuffer
• Math
• Describe the java.util package

4
Java API Specifications
http//java.sun.com/j2se/1.5.0/docs/api/
List of Packages
List of Classes
Package / Class Description
5
java.lang package

• java.lang provides classes that are fundamental
  to the design of the Java programming language.
• Object class, the root of the class hierarchy.
• Class class, represents classes at run time.
• Wrapper classes represent primitive types as
  objects.
• Math class provides mathematical functions.
• String and StringBuffer classes provide
  operations on strings.
• System classes provide system operations.
• Throwable class represents errors and exceptions.
• java.lang is implicitly imported in every Java
  source file.

6
Object class

• Declaration public class Object
• Class Object is the root of the class hierarchy.
  Every class has Object as a superclass. All
  objects inherit the methods of this class.

Method Summary Method Summary
protected  Object clone()
 boolean equals(Object obj)
protected  void finalize()
 Classlt? extends Objectgt getClass()
 int hashCode()
 void notify()
 void notifyAll()
 String toString()
 void wait()
 void wait(long timeout)
 void wait(long timeout, int nanos)
7
Class class

• Declaration public final class Class extends
  Object
• implements Serializable, GenericDeclaration,
  Type, AnnotatedElement
• Instances of the class Class represent classes
  and interfaces in a running Java application.
• Every array also belongs to a class that is
  reflected as a Class object that is shared by all
  arrays with the same element type and number of
  dimensions.
• The primitive Java types (boolean, byte, char,
  short, int, long, float, and double), and the
  keyword void are also represented as Class
  objects.
• Class has no public constructor. Instead Class
  objects are constructed automatically by the Java
  Virtual Machine as classes are loaded in the
  class loader.

8
Class class
Method Summary (Partial List) Method Summary (Partial List)
static Class forName(String className)
 Class getClasses()
 Constructor getConstructors()
 Field getFields()
 Class getInterfaces()
 Method getMethods()
 int getModifiers()
 String getName()
 Package getPackage()
 String getSimpleName()
 Class getSuperclass()
 boolean isArray()
 boolean isInstance(Object obj)
 boolean isInterface()
 boolean isLocalClass()
 boolean isMemberClass()
 boolean isPrimitive()
9
System class

• Declaration public final class System extends
  Object
• The System class contains several useful class
  fields and methods which are related to the
  following operations
• standard input, standard output, and error output
  streams.
• access to externally defined properties and
  environment variables.
• a means of loading files and libraries.
• and a utility method for quickly copying a
  portion of an array.

10
System class
Method Summary (Partial List) Method Summary (Partial List)
static void arraycopy(Object src, int srcPos, Object dest, int destPos, int length)
static String clearProperty(String key)
static long currentTimeMillis()
static void exit(int status)
static void gc()
static MapltString,Stringgt getenv()
static String getenv(String name)
static Properties getProperties() .
static SecurityManager getSecurityManager()
static void load(String filename)
static long nanoTime()
static void runFinalization()
static void runFinalizersOnExit(boolean value)
static void setErr(PrintStream err)
static void setIn(InputStream in)
static void setOut(PrintStream out)
static void setProperties(Properties props)
static void setSecurityManager(SecurityManager s)
Field Summary Field Summary
static PrintStream err
static InputStream in
static PrintStream out
11
String class

• Declaration public final class String extends
  Object implements Serializable,
  ComparableltStringgt, CharSequence
• The String class represents character strings.
  All string literals in Java programs are
  implemented as instances of this class.
• Strings are immutable, their values cannot be
  changed after they are created
• The class String includes methods for examining
  individual characters of the sequence, for
  comparing strings, for searching strings, for
  extracting substrings, and for creating a copy of
  a string with all characters translated to
  uppercase or to lowercase.

12
String class
Method Summary (Partial List) Method Summary (Partial List)
 char charAt(int index)
 int compareTo(String anotherString)
 String concat(String str)
 boolean contains(CharSequence s)
 boolean endsWith(String suffix)
 boolean equals(Object anObject)
static String format(String format, Object... args)
 int hashCode()
 int indexOf(int ch)
 int length()
 boolean matches(String regex)
 String replace(char oldChar, char newChar)
 String split(String regex)
 boolean startsWith(String prefix)
 String substring(int beginIndex)
 String toLowerCase()
 String toUpperCase()
 String trim()
13
StringBuffer class

• Declaration public final class StringBuffer
• extends Object implements Serializable,
  CharSequence
• StringBuffer is a thread-safe, mutable sequence
  of characters. A StringBuffer is like a String,
  but can be modified.
• StringBuffer class has been supplemented with an
  equivalent class designed for use by a single
  thread, StringBuilder.
• The StringBuilder class should generally be used
  in preference to StringBuffer as it supports all
  of the same operations but is faster as it
  performs no synchronization.

14
StringBuffer class
Method Summary (Partial List) Method Summary (Partial List)
 StringBuffer append(String str)
 StringBuffer append(StringBuffer sb)
 int capacity()
 char charAt(int index)
 StringBuffer delete(int start, int end)
 StringBuffer deleteCharAt(int index)
 int indexOf(String str)
 StringBuffer insert(int offset, String str)
 int lastIndexOf(String str)
 int length()
 StringBuffer replace(int start, int end, String str)
 StringBuffer reverse()
 void setCharAt(int index, char ch)
 void setLength(int newLength)
 String substring(int start)
 String substring(int start, int end)
 String toString()
 void trimToSize()
15
Math class

• Declaration public final class Math extends
  Object
• Math class contains methods for performing basic
  numeric operations such as elementary
  exponential, logarithm, square root, and
  trigonometric functions.
• Math class cannot be extended (it is declared
  final) nor instantiated (its constructor is
  private).
• Its methods are declared static and can be
  invoked using its class name.

16
Math class
Method Summary (Partial List) Method Summary (Partial List)
static double abs(double a)
static double ceil(double a)
static double cos(double a)
static double exp(double a)
static double floor(double a)
static double log(double a)
static double log10(double a)
static double log1p(double x)
static double max(double a, double b)
static double min(double a, double b)
static double pow(double a, double b)
static double random()
static long round(double a)
static double sin(double a)
static double sqrt(double a)
static double tan(double a)
static double toDegrees(double angrad)
static double toRadians(double angdeg)
Field Summary Field Summary
static double E
static double PI
17
Wrapper Classes

• The wrapper classes serve two primary purposes
• To provide a mechanism to "wrap" primitive values
  in an object so that the primitives can be
  included in activities reserved for objects, such
  as being added to collections, or returned from a
  method with an object return value.
• To provide an assortment of utility functions for
  primitives. Most of these functions are related
  to various conversions converting primitives to
  and from String objects, and converting
  primitives and String objects to and from
  different bases (or radix), such as binary,
  octal, and hexadecimal.

18
Wrapper Classes Constructors
19
java.util package

• Contains classes related to the following
• Collections framework
• Legacy collection classes
• Event model
• Date and time facilities
• Internationalization
• Miscellaneous utility classes
• StringTokenizer, random-number generator, and bit
  array

20
Key Points

• The Java API is prewritten code organized into
  packages of similar topics
• java.lang provides classes that are fundamental
  to the design of the Java programming language
• java.lang contains the following classes Object,
  Class, Math, String, StringBuffer,
  Throwable,Wrapper classes and System classes
• java.lang package is implicitly imported in every
  Java source file
• Object is the superclass of all classes
• String objects are immutable
• java.util contains classes related to the
  following
• Collections framework
• Legacy collection classes
• Event model
• Date and time facilities
• Internationalization
• Miscellaneous utility classes