Download Introduction to JAVA

INTRODUCTION TO JAVA
CHAPTER 1
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WHAT IS JAVA ?
• Java is a programming language and computing platform first
released by Sun Microsystems in 1995.
• The language derives much of its syntax from C
and C++ but has a simpler object model and fewer lowlevel facilities.
• The Java language is accompanied by a library of extra
software that we can use when developing programs.
• The library provides the ability to create graphics,
communicate over networks, and interact with databases.
• The set of supporting libraries is huge.
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JAVA APPLICATIONS AND APPLETS
Applications – standalone Java programs
Applets – Java programs that run inside web browsers
Java is the first programming language to deliberately embrace
the concept of writing programs that
can be executed on the Web.
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COMPILING JAVA PROGRAMS
 The Java compiler produces bytecode (a “.class” file) not machine
code from the source code (the “.java” file).
 Bytecode is converted into machine code using a Java
Interpreter
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PLATFORM INDEPENDENT JAVA
PROGRAMS COMPILING
 You can run bytecode on any computer that has a Java
Interpreter installed
“Hello.java”
“Hello.class”
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FUNDAMENTALS
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HELLO WORLD JAVA PROGRAM
// import section
public class MyFirstprogram {
// main method
public static void main( String args[] ){
System.out.println(“Hello World”);
} // end main
} // end class
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SAVING, COMPILING AND RUNNING JAVA
PROGRAMS
 Saving a Java program :
 A file having a name same as the class name should be used to
save the program. The extension of this file is ”.java”.
“MyFirstprogram.java”.
 Compiling a Java program : Call the Java compiler javac
The Java compiler generates a file called” MyFirstprogram.class”
(the bytecode).
 Running a Java program
 Call the Java Virtual Machine java:
• java MyFirstprogram.class
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COMMENTS IN A JAVA PROGRAM
• Comments are used to describe what your code does its
improve the code readability.
• The Java compiler ignores them.
• Comments are made using
 // which comments to the end of the line,
 /* */, everything inside of it is considered a comment
(including multiple lines).
 Examples:
/* This comment begins at this line.
This line is included in this comment
It ends at this line. */
// This comment starts here and ends at the end of this line.
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GOOD PROGRAMMING PRACTICE
• Be careful java is a sensitive language.
• It is good to begin every program with a comment that states the
purpose of the program and the author.
• Every java program consist of at least one class that the
programmer define.
• Begin each class name with capital letter.
• The class name doesn’t begin with a digit and doesn’t contain a
space.
• Use blank lines and spaces to enhance program readability
• When you type an opining left brace{ immediately type
the closing right brace}
• Indent the entire body of each class declaration
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PROGRAMS AND DATA
 Most programs require the temporary storage of data. The
data to be processed is stored in a temporary storage in the
computer's memory: space memory.
 A space memory has three characteristics
• Identifier
• Data Type
• State
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IDENTIFIER
is a sequence of characters that denotes the name of the space memory to be used.
•This name is unique within a program.
Identifier Rules
•It cannot begin with a digit (0 – 9).
•It may contain the letters a to z, A to Z, the digits 0 to 9, and the underscore
symbol, _.
•No spaces or punctuation, except the underscore symbol, _, are allowed.
Identifiers in Java are case-sensitive. The identifiers myNumber and mynumber, are seen
as two different identifiers by the compiler.
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STATE
My be changed
 variable
All lowercase.
Capitalizing the first letter of each word in a multiword identifier, except for the
first word.
Cannot be changed  constant
All uppercase, separating words within a multiword identifier with the
underscore symbol, _.
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DATA TYPE
•The data type defines what kinds of values a space memory is allowed to
store.
•All values stored in the same space memory should be of the same data
type.
•All constants and variables used in a Java program must be defined prior to
their use in the program.
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JAVA BUILT-IN DATA TYPES
Constant or Variable
First Decision Level
Second Decision Level
Third Decision Level
Integer
Boolean
Character
Numeric
Floating-point
byte
float
short
double
char
String
boolean
Fourth Decision Level
int
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long
PRIMITIVE DATA TYPES
Size
(bits)
Type
boolean
Range
Description
true, false
Stores a value that is either
true or false.
char
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0 to 65535
Stores a single 16-bit Unicode
character.
byte
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-128 to +127
Stores an integer.
short
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-32768 to +32767
Stores an integer.
int
32 bits
-2,147,483,648 to
+2,147,483,647
Stores an integer.
long
64 bits
-9,223,372,036,854,775,808
to
+9,223,372,036,854,775,807
Stores an integer.
float
32 bits
accurate to 8 significant digits
Stores a single-precision
floating point number.
double
64 bits
accurate to 16 significant digits
Stores a double-precision
floating point number.
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VARIABLE/CONSTANT DECLARATION
 When the declaration is made, memory space is allocated to
store the values of the declared variable or constant.
 The declaration of a variable means allocating a space
memory which state (value) may change.
 The declaration of a constant means allocating a space
memory which state (value) cannot change.
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CONSTANT DECLARATION
final dataType constIdentifier = literal | expression;
final double PI
= 3.14159;
final int
MONTH_IN_YEAR
= 12;
final short FARADAY_CONSTANT = 23060;
These are called
literals.
final int MAX
= 1024;
final int MIN
= 128;
final int AVG
= (MAX + MIN) / 2;
This is called
expression.
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VARIABLE DECLARATION
 A variable may be declared:
 With initial value.
 Without initial value
 Variable declaration with initial value;
dataType variableIdentifier = literal | expression;
double avg
int
i
int
= 0.0;
= 1;
x =5, y = 7, z = (x+y)*3;
 Variable declaration without initial value;
dataType variableIdentifier;
double avg;
int
i;
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MORE DECLARATION EXAMPLES
 String declaration
 with initial value:
 String word="Apple";
 without initial value:
 String word;

Boolean declaration:
 with initial value:
 boolean flag=false;
 boolean valid=true;
 without initial value:
 boolean flag;
 char declaration
 with initial value:
 char symbol ='*';
 without initial value:
 char symbol;
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VARIABLES
 Float
 The default type of floating point numbers is double .
 The declaration :
float rate = 15.5f ;
without the f , the compiler will generate an error
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VARIABLES
 Char

When using the char data type, you enclose each character represented within single
quotations marks.

Ex:
char c = ‘A’
char space = ‘ ‘

Each character is represented by a value (‘A’ is represented by the value 65)
char aCharecter='A';
char aAscii =65;
System.out.println(aCharecter);
System.out.println(aAscii);
A
A
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TYPE CONVERSION (CASTING)
 Used:
• to change one data type to another .
• to avoid implicit type correction.
 Syntax:
(dataTypeName) expression
 Expression evaluated first, then the value is converted to
dataTypeName
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TYPE CONVERSION (CASTING)

Examples:
1. (int)(7.9 + 6.7) = 14
2. (int)(7.9) + (int)(6.7) = 13
3. (double)(17) = 17.0
4. (double)(7) /2 = 7.0/2 = 3.5
5. (double)(7/2) = 3.0
6. (int)(7.8+(double)(15)/2) =(int)15.3 =15
double x=7.9 ,y= 6.7;
int result;
result=(int)(7.9 + 6.7);
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TYPE CONVERSION (CASTING)
8. (int)(‘A’)
9. (int)(‘8’)
10. (char)(65)
11. (char)(56)
= 65
= 56
= ‘A’
= ‘8’
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THE CLASS STRING
 Contains operations to manipulate strings.
 String:
 Sequence of zero or more characters.
 Enclosed in double quotation marks.
 Is processed as a single unit .
 Null or empty strings have no characters. “ “
 Every character has a relative position , the first character is in position
0.
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THE CLASS STRING
 Java system automatically makes the class String available (i.e no need
to import this class )
 Example :
Consider the following declaration :
String
sentence ;
sentence = “programming with java”
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Java Programming: From Problem Analysis to Program Design, Second Edition
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THE CLASS STRING
 Length of the string is the number of characters in it .
 When determining the length of a string , blanks count
.
 Example :
 “ “  has length = 0
 “abc”  has length = 3 , position of a = 0 ,b= 1 , c= 2
 “a boy”  has length = 5
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SOME COMMONLY USED STRING METHODS
String mystr=new String("programming with Java is fun");
System.out.println(mystr);
System.out.println(mystr.charAt(3));
System.out.println(mystr.indexOf('J'));
System.out.println(mystr.indexOf(‘j'));
programming with Java is fun
g
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-1
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Java Programming: From Problem Analysis to Program Design, Second Edition
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SOME COMMONLY USED STRING METHODS
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Java Programming: From Problem Analysis to Program Design, Second Edition
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EXAMPLE
String mystr=new String("programming with Java is fun");
System.out.println(mystr);
System.out.println(mystr.indexOf('a',10));
System.out.println(mystr.indexOf("with"));
System.out.println(mystr.indexOf("ing"));
programming with Java is fun
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12
8
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SOME COMMONLY USED STRING METHODS
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Java Programming: From Problem Analysis to Program Design, Second Edition
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EXAMPLES ON STRING METHODS
String s1 , s2 , s3 ;
s1 = “abcdefeg” ;
System.out.println( s1.length() );
// 8
System.out.println(s1.charAt(3));
//d
System.out.println(s1.indexOf(‘e’));
//4
System.out.println(s1.indexOf(“cd”)); //2
System.out.println(s1.toUpperCase()); //ABCDEFEG
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Java Programming: From Problem Analysis to Program Design, Second Edition
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EXAMPLES ON STRING METHODS
System.out.println(s1.substring(1 , 4)); //bcd
System.out.println(s1 + “xyz”); // abcdefegxyz
System.out.println( s1.replace(‘d’ ,’D’)); // abcDefeg
System.out.println(s1.charAt(4) );
// e
System.out.println(s1.indexOf(‘b’));
System.out.println(s1.indexOf(‘e’,5));
// 1
// 6
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