1. Introduction to Java API
ATS Application Programming: Java Programming
Introduction to Java API
5.1 Introduction to Java API
Java API Specifications
java.lang package
Object class
Class class
System class
String and StringBuffer classes
Math class
java.util package
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Course Code #Z16325

2. ATS Application Programming: Java Programming
Objectives
5.1 Introduction to Java API
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
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Course Code #Z16325

3. Java API Specifications
ATS Application Programming: Java Programming
Java API Specifications
5.1 Introduction to Java API
List of Packages
List of Classes
Notes:
The Java Application Programming Interface (API) is prewritten code, organized into packages of similar topics
Official website:
Package / Class Description
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Course Code #Z16325

4. ATS Application Programming: Java Programming
java.lang package
5.1 Introduction to Java API
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.
Notes:
wrapper classes: Boolean, Character, Short, Integer, Long, Float, and Double
System operations classes: ClassLoader, Process, Runtime, SecurityManager, and System
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Course Code #Z16325

5. ATS Application Programming: Java Programming
Object class
5.1 Introduction to Java API
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
protected  Object
clone()
 boolean
equals(Object obj)
protected  void
finalize()
 Class<? extends Object>
getClass()
 int
hashCode()
 void
notify()
notifyAll()
 String
toString()
wait()
wait(long timeout)
wait(long timeout, int nanos)
For the definitions of the methods, please refer to Java API Specifications
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Course Code #Z16325

6. ATS Application Programming: Java Programming
Class class
5.1 Introduction to Java API
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.
For the definitions of the methods, please refer to Java API Specifications
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Course Code #Z16325

7. ATS Application Programming: Java Programming
Class class
5.1 Introduction to Java API
Method Summary (Partial List)
static Class
forName(String className)
 Class[]
getClasses()
 Constructor[]
getConstructors()
 Field[]
getFields()
getInterfaces()
 Method[]
getMethods()
 int
getModifiers()
 String
getName()
 Package
getPackage()
getSimpleName()
 Class
getSuperclass()
 boolean
isArray()
isInstance(Object obj)
isInterface()
isLocalClass()
isMemberClass()
isPrimitive()
For a complete list of methods, please refer to Java API Specifications
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Course Code #Z16325

8. ATS Application Programming: Java Programming
System class
5.1 Introduction to Java API
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.
For the definitions of the methods, please refer to Java API Specifications
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Course Code #Z16325

9. ATS Application Programming: Java Programming
System class
5.1 Introduction to Java API
Field Summary
static PrintStream
err
static InputStream in
out
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()
exit(int status)
gc()
static Map<String,String>
getenv()
getenv(String name)
static Properties
getProperties() .
static SecurityManager
getSecurityManager()
load(String filename)
nanoTime()
runFinalization()
runFinalizersOnExit(boolean value)
setErr(PrintStream err)
setIn(InputStream in)
setOut(PrintStream out)
setProperties(Properties props)
setSecurityManager(SecurityManager s)
For a complete list of methods, please refer to Java API Specifications
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Course Code #Z16325

10. ATS Application Programming: Java Programming
String class
5.1 Introduction to Java API
Declaration: public final class String extends Object implements Serializable, Comparable<String>, 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.
For the definitions of the methods, please refer to Java API Specifications
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Course Code #Z16325

11. ATS Application Programming: Java Programming
String class
5.1 Introduction to Java API
Method Summary (Partial List)
 char
charAt(int index)
 int
compareTo(String anotherString)
 String
concat(String str)
 boolean
contains(CharSequence s)
endsWith(String suffix)
equals(Object anObject)
static String
format(String format, Object... args)
hashCode()
indexOf(int ch)
length()
matches(String regex)
replace(char oldChar, char newChar)
 String[]
split(String regex)
startsWith(String prefix)
substring(int beginIndex)
toLowerCase()
toUpperCase()
trim()
Talking Points:
The most common constructor simply takes another string (often a literal) as its argument, as follows:
String myString = new String(“My new string”);
OR String myString = “My new string”;
You should be aware of what happens when you use a string literal in this manner:
Every string literal is represented internally by an instance of String
Java classes have a pool of such strings called String Constant Pool
During compilation, the compiler adds an appropriate string to the pool, unless there is one already there (the literal has already been used in the class), in which case it reuses that
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Course Code #Z16325

12. ATS Application Programming: Java Programming
StringBuffer class
5.1 Introduction to Java API
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.
For the definitions of the methods, please refer to Java API Specifications
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Course Code #Z16325

13. ATS Application Programming: Java Programming
StringBuffer class
5.1 Introduction to Java API
Method Summary (Partial List)
 StringBuffer
append(String str)
append(StringBuffer sb)
 int
capacity()
 char
charAt(int index)
delete(int start, int end)
deleteCharAt(int index)
indexOf(String str)
insert(int offset, String str)
lastIndexOf(String str)
length()
replace(int start, int end, String str)
reverse()
 void
setCharAt(int index, char ch)
setLength(int newLength)
 String
substring(int start)
substring(int start, int end)
toString()
trimToSize()
A StringBuffer object represents a string that can be dynamically modified
Its three constructors are:
StringBuffer() – creates an empty buffer
StringBuffer(int capacity) – creates an empty buffer of the length specified
StringBuffer(String initial) – creates a buffer initially populated with the specified string
One of the properties of a StringBuffer is its capacity, which is the maximum length string it can contain without needing more memory – However, it can grow beyond this capacity as and when required so it is not necessary to worry about it.
Faculty Notes:
StringBuffer needs more memory than String, but if many operations are being performed, StringBuffer takes less memory than the many Strings that would be the byproduct when still using String
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Course Code #Z16325

14. ATS Application Programming: Java Programming
Math class
5.1 Introduction to Java API
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.
Faculty note:
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Course Code #Z16325

15. ATS Application Programming: Java Programming
Math class
5.1 Introduction to Java API
Method Summary (Partial List)
static double
abs(double a)
ceil(double a)
cos(double a)
exp(double a)
floor(double a)
log(double a)
log10(double a)
log1p(double x)
max(double a, double b)
min(double a, double b)
pow(double a, double b)
random()
static long
round(double a)
sin(double a)
sqrt(double a)
tan(double a)
toDegrees(double angrad)
toRadians(double angdeg)
Field Summary
static double E PI
Talking Points:
A StringBuffer object represents a string that can be dynamically modified
Its three constructors are:
StringBuffer() – creates an empty buffer
StringBuffer(int capacity) – creates an empty buffer of the length specified
StringBuffer(String initial) – creates a buffer initially populated with the specified string
One of the properties of a StringBuffer is its capacity, which is the maximum length string it can contain without needing more memory – however, as it can grow beyond this capacity as and when required, it is not necessary to worry about it
Faculty Notes:
StringBuffer needs more memory than String, but if many operations are being performed, StringBuffer takes less memory than the many Strings that would be the byproduct when still using String
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Course Code #Z16325

16. ATS Application Programming: Java Programming
Wrapper Classes
5.1 Introduction to Java API
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.
Faculty Notes:
Describe the significance of wrapper classes, including making appropriate selections in the wrapper classes to suit specified behavior requirements, stating the result of executing a fragment of code that includes an instance of one of the wraper classes, and writing code using the following methods of wrapper classes (e.g. Integer, Double, etc.): doubleValue, floatValue, intValue, longValue, parseXxx, getXxx, toString, toHexString.
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Course Code #Z16325

17. Wrapper Classes Constructors
ATS Application Programming: Java Programming
Wrapper Classes Constructors
5.1 Introduction to Java API
short or String
Short
short
long or String
Long
long
int or String
Integer
int
float, double, or String
Float
float
double or String
Double
double
char
Character
byte of String
Byte
byte
boolean or String or null
Boolean
boolean
Constructor Arguments
Wrapper Class
Primitive
Faculty Notes:
Wrapper classes is one of the features of Java that complies with Object Oriented Programming. Primitive data types can be encapsulated and manipulated using these Wrapper Classes.
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Course Code #Z16325

18. ATS Application Programming: Java Programming
java.util package
5.1 Introduction to Java API
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
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Course Code #Z16325

19. ATS Application Programming: Java Programming
Key Points
5.1 Introduction to Java API
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
© Accenture All Rights Reserved
Course Code #Z16325