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1
JAVA PROGRAMMING
2 - Introduction to Java Applications
Indriani Noor Hapsari, ST, MT
Contents
2

Introduction

A First Program in Java

Text Displaying

Value Input: Integer Addition

Arithmetic

Equality and Relational Operators
Keywords

keyword: An identifier that you cannot use because it
already has a reserved meaning in Java.
abstract
boolean
break
byte
case
catch
char
class
const
continue
default
do
double
else
extends
final
finally
float
for
goto
if
implements
import
instanceof
int
interface
long
native
new
package
private
protected
public
return
short
static
strictfp
super
switch
synchronized
this
throw
throws
transient
try
void
volatile
while
Introduction
4

Identifier Rule
 Series
of characters consisting of letters, digits,
underscores ( _ ) and dollar signs ( $ )
Identifier = (letter | '_' | ' $ ') {letter | digit | '_'}.
 “Welcome1”,
 “7button”
 Case
 a1
“$value”, “_value”, “button7” are valid
is invalid
sensitive (capitalization matters)
and A1 are different
Introduction
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
Primitive Data Type
Data Type
Purpose
Contents
Default Value*
boolean
Truth value
true or false
false
char
Character
Unicode characters
\u0000
byte
Signed integer
8 bit two's complement
(byte) 0
short
Signed integer
16 bit two's complement
(short) 0
int
Signed integer
32 bit two's complement
0
long
Signed integer
64 bit two's complement
0L
float
Real number
32 bit IEEE 754 floating point
0.0f
double
Real number
64 bit IEEE 754 floating point
0.0d
A First Program in Java
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
Function: printing a line of text
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// Fig. 2.1: Welcome1.java
// Text-printing program.
public class Welcome1 {
// main method begins execution of Java application
public static void main( String args[] )
{
System.out.println( "Welcome to Java Programming!" );
} // end method main
} // end class Welcome1
Welcome to Java Programming!
A First Program in Java
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
Comments
 //
remainder of line is comment
 Comments
ignored
 Document and describe code
1 // Fig. 2.1: Welcome1.java
 Multiple
line comments: /* ... */
/*
This is a multiple line comment.
It can be split over many lines
*/
A First Program in Java
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
Class Declaration
4 public class Welcome1 {
 Every
Java program has at least one defined class
 Keyword:
words reserved for use by Java
 class
 The
 Naming
keyword followed by class name
class name has to be an identifier
Convention: capitalize every word
 Example:
SampleClassName
A First Program in Java
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
Body Delimiter
 Left
brace {
 Begins
body of every class
 A corresponding right brace “}” ends definition (line 13)
4 public class Welcome1 {
13}/* End of Class Welcome1 */
 Indentation
Convention
 Whenever
you type an left brace “{“, immediately type the
right brace “}”.
 Then,
indent to begin type the body.
A First Program in Java
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
Program Entry
 Applications
 Exactly
one method must be called main
 Parenthesis
 Java
5
begin executing at main()
indicate main is a method
applications contain one or more methods
public static void main( String args[] )
 Methods
can perform tasks and return result
means main returns no information
 args[]:input arguments in String data type.
 void:
A First Program in Java
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
Statements
 Statements
are instructions to commend hardware to
perform some operations.
 It must end with semicolon “;”
7
System.out.println("Welcome to Java
Programming!" );
standard output object
 System.out.println: displays line of text
 System.out:
A First Program in Java
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
Execution Steps
JAVA PROGRAM EXECUTION
Java
source code
Java
compiler
Welcome.java
javac Welcome.java
byte-code
.class
byte-code
interpreter
JVM
java Welcome EXECUTION
A First Program in Java
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
Execution Steps
 Compiling
 Open
 Type
 If
a program
a command window, go to program’s directory.
javac Welcome.java
no errors, Welcome.class created
 Executing
a program
 Type
java Welcome to start JVM and then run the
program Welcome.class
 Interpreter
calls method main
A First Program in Java
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

Demonstration
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public class Welcome1 {
// main method begins execution of Java application
public static void main( String args[] )
{
System.out.println( "Welcome to Java Programming!" );
} // end method main
} // end class Welcome1
Text Displaying
15

Displaying Methods
 System.out.println
 Prints
argument, puts cursor on new line
 System.out.print
 Prints
argument, keeps cursor on same line
 System.out.printf
 Prints
7
8
argument which is a format string
System.out.print("Welcome
toto
“);
System.out.println("Welcome
Java
System.out.println(“JavaProgramming!"
Programming!");
);
Text Displaying
16

Escape Sequences
 The
backslash “\” is called an escape character to
indicate a “special character” is to be output.
 Backslash
combined with character makes escape
sequence.
Escape Sequence
Description
\n
Newline
\t
Horizontal Tab
\r
Carriage Return. Position the cursor at the beginning of the
current line
\\
Backslash
\”
Double Quote
Text Displaying
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
7
Escape Sequences
System.out.println("Welcome\nto\nJava\n
Programming!" );
Welcome
to
Java
Programming!
7
System.out.println(“\”in quotes\”" );
“in quotes”
Text Displaying
18

Format String
 The
first argument of printf() is a format string
 Fixed
Text
 Format
Specifier
 Format
specifier is a placeholder for a value and
specifies the type of data.
 Percent
Sign (“%”)
 Data Type
Text Displaying
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
Format String
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Type Character Input
String Result
%c
char
character
%d
signed int
signed decimal integer
%f
float
real number, standard notation
%s
string
string
System.out.printf(“%s\n%s\n”, “Welcome to”,
“Java Programming!" );
Welcome to
Java Programming!
Value Input: Integer Addition
20

Requirements
 Read
in two integers from users
 Compute the summation of them
 Print out the result on the screen
Enter first integer:1
Enter second integer:3
Sum is: 4
Value Input: Integer Addition
21

Variable Declaration
 Every
variable has a name, a type, a size and a value
 Name
corresponds to location in memory
 When
new value is placed into a variable, replaces
(and destroys) previous value
 Reading
them from memory does not change them
int number1=10;
int number1;
number1=10;
Value Input: Integer Addition
22

Variable Declaration
public class Addition {
// main method begins execution of Java application
public static void main( String args[] ){
int number1;
int number2;
int sum;
……
……
}/* End of main */
}/* End of class Addition */
Value Input: Integer Addition
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import java.util.Scanner;
public class Addition {
// main method begins execution of Java application
public static void main( String args[] ){
……
// create Scanner to obtain input from command window
Scanner input = new Scanner( System.in );
// read the first integer
System.out.print("Enter first integer:");
number1 = input.nextInt();
// read the second integer
System.out.print("Enter second integer:");
number2 = input.nextInt();
……
}/* End of main */
}/* End of class Addition */
Value Input: Integer Addition
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import java.util.Scanner;
public class Addition {
// main method begins execution of Java application
public static void main( String args[] ){
……
sum = number1 + number2;
System.out.printf("Sum is: %d\n", sum);}/* End of main */
}/* End of class Addition */
Arithmetic
25

Description
 Arithmetic
calculations used in most programs
 Asterisk
‘*’ indicates multiplication
 Percent sign ‘%’ is the remainder (modulus) operator
 Integer
division truncates remainder
7 / 5 evaluates to 1
 Modulus
operator % returns the remainder
7 % 5 evaluates to 2
Arithmetic
26

Operator precedence
 Some
arithmetic operators act before others
Operator(s)
Operation(s)
Order of evaluation (precedence)
()
Parentheses
*, /, or %
Multiplication
Division
Modulus
Addition
Subtraction
Evaluated first. If the parentheses
are nested, the expression in the
innermost pair is evaluated first. If
there are several pairs of parentheses
“on the same level” (i.e., not
nested), they are evaluated left to
right.
Evaluated second. If there are
several, they are
evaluated left to right.
Evaluated last. If there are several,
they are
evaluated left to right.
+ or -
Equality and Relational Operators
27

Description
A
condition is an expression that can be either true or
false.
 It
is used in control statements (if, for, while) to change
the execution flow of program
 Conditions
 Equality
can be formed by using
Operators
 Relational Operators
Equality and Relational Operators
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
Equality/Relational Operators
Standard
Algebraic
Java Equality
Sample
Meaning
=
==
x == y
x is equal to y?
!=
x != y
x is not equal to y ?
>
>
x>y
x is greater than y ?
<
<
x<y
x is less than y?
>=
x >= y
x is greater than or equal to y
<=
x <= y
x is less than or equal to y



Equality and Relational Operators
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
Example
import java.util.Scanner;
public class Comparison {
public static void main( String args[] ){
int number1=100;
int number2=200;
if(number1 == number2){
System.out.printf(“%d == %d \n”, number1, number2);
}/* End of if-condition */
if(number1 != number2){
System.out.printf(“%d != %d \n”, number1, number2);
}/* End of if-condition */
}/* End of main */
}/* End of class Addition */
CREATING FIRST
STATIC METHODS USING JAVA
Static methods

static method: A named group of statements.
class
denotes the structure of a program
 eliminates redundancy by code reuse



procedural decomposition:
dividing a problem into methods





Writing a static method is like
adding a new command to Java.



method A
statement
statement
statement
method B
statement
statement
method C
statement
statement
statement
Using static methods
1. Design the algorithm.
 Look
at the structure, and which commands are repeated.
 Decide what are the important overall tasks.
2. Declare (write down) the methods.
 Arrange
statements into groups and give each group a
name.
3. Call (run) the methods.
 The
program's main method executes the other methods to
perform the overall task.
Individual Assignment:
Drawing with methods

Write a program to print these figures using methods.
/
______
\
/
\
\
/
\______/
\
/
\______/
+--------+
______
/
\
/
|
\
\
STOP |
/
\______/
______
/
\
/
\
+--------+
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END OF SLIDES.