Introduction to Java
Viska Mutiawani, M.Sc
Java: History

Computers of the past
Java: History (2)

The invention of the microprocessor revolutionized computers
Intel microprocessor
Commodore Pet microcomputer
Java: History (3)

It was believed that the logical next step for microprocessors was
to have them run intelligent consumer electronics
Java History (4)
Sun
Microsystems funded an internal
research project “Green” to investigate this
opportunity.
◦ Result: A programming language called “Oak”
Java History (5)
◦ Problem: There was already a programming
language called Oak.
◦ The “Green” team met at a local coffee shop to
come up with another name...
Java!
Java: History (6)
The
concept of intelligent devices
didn’t catch on.
Project Green and work on the
Java language was nearly canceled.
Java: History (7)
The
popularity of the Internet resulted in Sun’s refocusing of Java on computers.
Prior to the advent of Java, web pages allowed you to
download only text and images.
Server containing a
web page
Your computer at
home running a web
browser
User clicks on a link
Images and text get downloaded
Java: History (8)


Java enabled web browsers allowed for the downloading of
programs (Applets).
Java is still used in this context today:
◦ Facebook (older version)
◦ Hotmail (older version)
Server containing
a web page
Your computer at
home running a web
browser
User clicks on a link
Java Applet downloaded
Java version of the Game of Life: http://www.bitstorm.org/gameoflife/
Online checkers:
http://www.darkfish.com/checkers/index.html
What is java?

Developed by Sun Microsystems (James Gosling)

A general-purpose object-oriented language

Based on C/C++

Designed for easy Web/Internet applications

Widespread acceptance
Java: Write Once, Run Anywhere

Consequence of Java’s history: platform-independence
Click on link to Applet
Mac user running Safari
Web page stored on Unix server
Virtual machine translates byte code to
native Mac code and the Applet is run
Byte code is downloaded
Windows user running Internet Explorer
Byte code
(part of web
page)
Java: Write Once, Run Anywhere

Consequence of Java’s history: platform-independent
Mac user running Safari
Click on link to Applet
Windows user running Internet Explorer
Virtual machine translates byte code to
native Windows code and the Applet is run
Web page stored on Unix server
Byte code is
downloaded
Java: Write Once, Run Anywhere (2)

But Java can also create standard (nonweb based) programs
Dungeon Master (Java version)
http://homepage.mac.com/aberfield/dmj/
Kung Fu Panda 2: THQ
Examples of mobile Java games: http://www.mobilegamesarena.net
Java: Write Once, Run Anywhere (3)


Java has been used by
large and reputable
companies to create
serious stand-alone
applications.
Example:
◦ Eclipse1: started as a
programming
environment created by
IBM for developing Java
programs. The program
Eclipse was itself written
in Java.
1 For more information: http://www.eclipse.org/downloads/
Compiled Programs With Different
Operating Systems
Windows
compiler
Executable (Windows)
Computer
program
Mac OS
compiler
Executable (Mac)
UNIX
compiler
Executable (UNIX)
A High Level View Of
Translating/Executing Java Programs
Stage 1: Compilation
Filename.java
Java program
Java compiler
(javac)
Filename.class
Java bytecode
(generic
binary)
A High Level View Of
Translating/Executing Java Programs (2)
Stage 2: Interpreting and executing the byte code
Filename.class
Java bytecode
(generic
binary)
Java interpreter
(java)
Machine language
instruction (UNIX)
Machine language
instruction (Windows)
Machine language
instruction (Apple)
Java Features (1)

Simple
◦
◦
◦
◦

fixes some clumsy features of C++
no pointers
automatic garbage collection
rich pre-defined class library
http://www.oracle.com/technetwork/java/javase/documentation/index.
html
Object oriented
◦
◦
◦
◦
focus on the data (objects) and methods manipulating the data
all functions are associated with objects
almost all datatypes are objects (files, strings, etc.)
potentially better code organization and reuse
Java Features (2)

Interpreted
◦ java compiler generate byte-codes, not native machine code
◦ the compiled byte-codes are platform-independent
◦ java bytecodes are translated on the fly to machine readable
instructions in runtime (Java Virtual Machine)

Portable
◦ same application runs on all platforms
◦ the sizes of the primitive data types are always the same
◦ the libraries define portable interfaces
Java Features (3)

Reliable
◦ extensive compile-time and runtime error checking
◦ no pointers but real arrays. Memory corruptions or unauthorized
memory accesses are impossible
◦ automatic garbage collection tracks objects usage over time

Secure
◦ usage in networked environments requires more security
◦ memory allocation model is a major defense
◦ access restrictions are forced (private, public)
Java Features (4)

Multithreaded
◦ multiple concurrent threads of executions can run simultaneously
◦ utilizes a sophisticated set of synchronization primitives (based on
monitors and condition variables paradigm) to achieve this

Dynamic
◦ java is designed to adapt to evolving environment
◦ libraries can freely add new methods and instance variables without any
effect on their clients
◦ interfaces promote flexibility and reusability in code by specifying a set
of methods an object can perform, but leaves open how these methods
should be implemented
◦ can check the class type in runtime
Java Disadvantages

Slower than compiled language such as C
◦ an experiment in 1999 showed that Java was 3 or 4 times slower
than C or C++
title of the article: “Comparing Java vs. C/C++ Efficiency Issues to
Interpersonal Issues” (Lutz Prechelt)
◦ adequate for all but the most time-intensive programs
Which Java?
Which Java?
Java Platform, Standard Edition (Java SE) lets you develop and deploy Java
applications ondesktops and servers, as well as in today's
demanding embedded environments. Java offers the rich user interface,
performance, versatility, portability, and security that today’s applicationsrequire.
Which Java?
Java
8+ (current is 8u20 version) JDK (Java
Development Kit), Standard Edition includes:
◦ JDK (Java development kit) – for developing Java
software (creating Java programs.)
◦ JRE (Java Runtime environment) – only good for
running pre-created Java programs.
Java Plug-in – a special version of the JRE designed to run
through web browsers.
http://www.oracle.com/technetwork/java/javase/downloads/index.html
Install JavaTM 2 Platform on your machine

Can be installed on different platforms:
◦ Unix/Linux
◦ Windows
◦ Mac OS

Follow the on-line instructions:
http://java.sun.com/docs/books/tutorial/getStarted/cupojava/index.html
Smallest Compilable And Executable
Java Program
The name of the online example is:
Smallest.java (Important note: file name matches the word after
the keyword ‘class’)
public class Smallest
{
public static void main (String[] args)
{
}
}
Creating, Compiling And Running Java
Programs On The Computer Science
Network
Java program
filename.java
Type it in with the text editor of your choice
(Unix file)
Java compiler
javac
Java byte code
filename.class
To compile the program at the
command line type "javac
filename.java"
(UNIX file)
Java Interpreter
java
To run the interpreter, at the
command line type "java filename"
Compiling The Smallest Java
Program
Smallest.java
public class Smallest
{
public static void main (String[] args)
{
}
}
Type “javac
Smallest.java”
javac
Smallest.class
(Java byte code)
10000100000001000
00100100000001001
:
:
Running The Smallest Java Program
Smallest.class
(Java byte code)
10000100000001000
00100100000001001
:
:
java
Type “java Smallest”
(Platform/Operating specific binary
10100111000001000
00100111001111001
:
:
Running The Java Compiler At
Home
After installing Java you will need to indicate to the
operating system where the java compiler has been
installed (‘setting the path’).
 For details of how to set your path variable for your
particular operating system try the Sun or Java website.
 Example of how to set the path in Windows:
◦ http://www.java.com/en/download/help/path.xml

Getting Started: (1)
(1) Create the source file:
◦ open a text editor, type in the code which defines a class
(HelloWorldApp) and then save it in a file (HelloWorldApp.java)
◦ file and class name are case sensitive and must be matched exactly
(except the .java part)
Example Code: HelloWorldApp.java
/**
* The HelloWorldApp class implements an application
* that displays "Hello World!" to the standard output
*/
public class HelloWorldApp {
public static void main(String[] args) {
// Display "Hello World!"
System.out.println("Hello World!");
}
}
Java is
CASE SENSITIVE!
Getting Started: (2)
(2) Compile the program:
◦ compile HelloWorldApp.java by using the following command:
javac HelloWorldApp.java
it generates a file named HelloWorldApp.class
‘javac’ is not recognized as an internal or
external command, operable program or hatch file.
javac: Command not found
if you see one of these errors, you have two choices:
1) specify the full path in which the javac program locates every time. For
example:
C:\j2sdk1.4.2_09\bin\javac HelloWorldApp.java
2) set the PATH environment variable
Getting Started: (3)
(3) Run the program:
◦ run the code through:
java HelloWorldApp
◦ Note that the command is java, not javac, and you refer to
HelloWorldApp, not HelloWorldApp.java or
HelloWorldApp.class
Exception in thread "main" java.lang.NoClassDefFoundError:
HelloWorldApp
if you see this error, you may need to set the environment variable
CLASSPATH.
Documentation / Comments
Multi-line documentation
/* Start of documentation
End of documentation
*/
Documentation for a single line
//Everything until the end of the line is a comment
Doc secara otomatis
Komentar yang dimulai dengan /** dan berakhir
dengan */ akan menghasilkan doc secara otomatis.
 javadoc yang disediakan dalam java akan
melakukan proses searching terhadap /** terhadap
file program, jika ketemu maka akan dibuat file
HTML untuk dokumentasi
 Contoh doc versi Java

Review: What Should You Document?
Program (or that portion of the program) author
What does the program as a while do e.g., tax
program.
 What are the specific features of the program e.g., it
calculates personal or small business tax.
 What are it’s limitations e.g., it only follows Canadian
tax laws and cannot be used in the US. In Canada it
doesn’t calculate taxes for organizations with yearly
gross earnings over $1 billion.
 What is the version of the program


◦ If you don’t use numbers for the different versions of your
program then consider using dates (tie versions with
program features).
Important Note

Each Java instruction must be followed by
a semi-colon!
General format
Examples
Instruction1;
int num = 0;
Instruction2;
System.out.println(num);
Instruction3;
:
:
:
:
Java Output
Format:
System.out.print(<string or variable name one> + <string or variable
name two>..);
OR
System.out.println(<string or variable name one> + <string or variable
name two>..);
Examples
public class OutputExample1
{
public static void main (String [] args)
{
int num = 123; // More on this shortly
System.out.println("Good-night gracie!");
System.out.print(num);
System.out.println("num="+num);
}
}
Output : Some Escape Sequences For
Formatting
Escape sequence
Description
\t
Horizontal tab
\r
Carriage return
\n
New line
\”
Double quote
\\
Backslash
Example Formatting Codes

Example: FormattingExample.java
public class FormattingExample
{
public static void main (String [] args)
{
System.out.print("lol\tz\n");
System.out.println("hello\rworld");
System.out.println("\"Geek\" talk slash (\\)
com");
}
}
Language basics

Data types
◦ 8 primitive types:
 boolean, byte, short, int, long, float, double, char
◦ Class types, either provided by Java, or made by programmers
 String, Integer, Array, Frame, Object, Person, Animal, …
◦ Array types

Variables
◦ dataType identifier [ = Expression]:
◦ Example variable declarations and initializations:
int x; x=5;
boolean b = true;
Frame win = new Frame();
String x = “how are you?”;
int[] intArray;
intArray = new int[2];
intArray[0] = 12;
intArray[1] = 6;
Person pArray = new Person[10];
Variables


Variables must be declared before they can be used.
Variable declaration:
◦ Creates a variable in memory.
◦ Specify the name of the variable as well as the type of
information that it will store.
◦ E.g. int num;
◦ Although requiring variables to be explicitly declared
appears to be an unnecessary chore it can actually be
useful for minimizing insidious logic errors.

Using variables
◦ Only after a variable has been declared can it be used.
◦ E.g., num = 12;
Declaring Variables: Syntax

Format:
<type of information> <name of variable>;

Example:
char myFirstInitial;

Variables can be initialized (set to a
starting value) as they’re declared:
char myFirstInitial = ‘j’;
int age = 30;
Some Built-In Types Of Variables In
Java
Type
Description
byte
8 bit signed integer
short
16 but signed integer
int
32 bit signed integer
long
64 bit signed integer
float
32 bit signed real number
double
64 bit signed real number
char
16 bit Unicode character (ASCII and
beyond)
boolean
1 bit true or false value
String
A sequence of characters between double
quotes ("")
Location Of Variable Declarations
public class <name of class>
{
public static void main (String[] args)
{
// Local variable declarations occur here
<< Program statements >>
:
:
}
}
Style Hint: Initializing Variables

Always initialize your variables prior to using them!
◦ Do this whether it is syntactically required or not.

Example how not to approach:
public class OutputExample1
{
public static void main (String [] args)
{
int num;
System.out.print(num);
}
}
OutputExample1.java:7: error: variable
num might not have been initialized
System.out.print(num);
^
Boolean
Tipe data boolean hanya bernilai true dan
false.
 Digunakan untuk menguji ungkapan, dapat
digunakan pada seleksi dan looping
 Dalam bahasa C tidak ada jenis data boolean.
Biasanya 0 dan 1 (atau bukan nol) digunakan
untuk mewakili nilai benar dan salah
 Dalam C++, jenis data bool digunakan

Boolean: contoh
boolean lapar;
lapar = true;
while(lapar){
System.out.println(“Kasih Makan dong...”);
lapar = false;
}
◦ lapar hanya mungkin bernilai true/false.
◦ Looping while akan berhenti apabila nilai lapar
bernilai false.
Explicit Casting
Ada kalanya kita ingin menganggap variable bernilai
double sebagai integer
 Contoh:

◦ double hasilBagi = 20.997;
◦ int hasil = (int) hasilBagi;

Nilai hasil adalah 20. Artinya terdapat data yang
akan hilang.
Rounding/Pembulatan




Dalam Java, kita bisa membulatkan suatu nilai double/float
kepada integer terdekat, kita bisa menggunakan method
Math.round
◦ double nilaiRata2 = 20.997;
◦ int hasilPembulatan=(int) Math.round(nilaiRata2);
Nilai hasilPembulatan ialah 21 setelah dibulatkan.
Penggunaan casting (int) masih diperlukan karena nilai yang
dikembalikan oleh method round berjenis long.
Kita perlu tukarkan long kepada int, menggunakan casting.
Implicit Casting

Java membolehkan penukaran hasil suatu tipe data
tanpa menggunakan proses casting mengikuti
urutan berikut:
◦ byte  short  int  long  float  double
◦ char  int
**(dibaca: byte boleh ditukar kepada short
short boleh ditukar kepada int.. dll)
int x = 10; // occupies 4 bytes
double y = x; // occupies 8 bytes
System.out.println(y); // prints 10.0
Java Constants
Reminder: constants are like variables in
that they have a name and store a certain
type of information but unlike variables they
CANNOT change.
Format:
final <constant type> <CONSTANT NAME> = <value>;
Example:
final int SIZE = 100;
Location Of Constant Declarations
public class <name of class>
{
public static void main (String[] args)
{
// Local constant declarations occur here (more later)
// Local variable declarations
< Program statements >>
:
:
}
}
Why Use Constants?
1.
They make your program easier to read and
understand
populationChange = (0.1758 – 0.1257) *
currentPopulation;
Vs.
final float BIRTH_RATE = 17.58;
final float MORTALITY_RATE = 0.1257;
int currentPopulation = 1000000;
populationChange = (BIRTH_RATE MORTALITY_RATE) * currentPopulation;
Why Use Constants? (2)
2.
It can make your program easier to
maintain (update with changes).
◦ If the constant is referred to several times
throughout the program, changing the value of
the constant once will change it throughout
the program.
Why Use Constants? (3)
final float BIRTH_RATE = 0.1758;
final float MORTALITY_RATE = 0.1257;
float populationChange = 0;
float currentPopulation = 1000000;
populationChange = (BIRTH_RATE - MORTALITY_RATE) * currentPopulation;
if (populationChange > 0)
System.out.println("Increase“)
System.out.println("Birth rate:“+ BIRTH_RATE + " Mortality rate:“ +
MORTALITY_RATE, " + Population change:“ + populationChange);
else if (populationChange < 0)
System.out.println("Decrease“);
System.out.println("Birth rate:“+BIRTH_RATE, “+Mortality rate:“+
MORTALITY_RATE
+"Population change:“+populationChange);
else
System.out.print("No change“);
System.out.print("Birth rate:“+BIRTH_RATE, “+Mortality rate:“+
MORTALITY_RATE+
"Population change:“+populationChange);
Why Use Constants? (4)
One change in the
initialization of the
constant changes all
references to that
constant.
final float BIRTH_RATE = 0.5;
final float MORTALITY_RATE = 0.1257;
float populationChange = 0;
float currentPopulation = 1000000;
populationChange = (BIRTH_RATE - MORTALITY_RATE) * currentPopulation;
if (populationChange > 0)
System.out.println("Increase“)
System.out.println("Birth rate:“+ BIRTH_RATE + " Mortality rate:“ +
MORTALITY_RATE, " + Population change:“ + populationChange);
else if (populationChange < 0)
System.out.println("Decrease“);
System.out.println("Birth rate:“+BIRTH_RATE, “+Mortality rate:“+
MORTALITY_RATE
+"Population change:“+populationChange);
else
System.out.print("No change“);
System.out.print("Birth rate:“+BIRTH_RATE, “+Mortality rate:“+
MORTALITY_RATE+
"Population change:“+populationChange);
Variable Naming Conventions In
Java
 Compiler
requirements
◦ Can’t be a keyword nor can the names of the special constants:
true, false or null be used
◦ Can be any combination of letters, numbers, underscore or
dollar sign (first character must be a letter or underscore)
 Common
stylistic conventions
◦ The name should describe the purpose of the variable
◦ Avoid using the dollar sign
◦ With single word variable names, all characters are lower case
e.g., double grades;
◦ Multiple words are separated by capitalizing the first letter of
each word except for the first word
e.g., String firstName = “James”;
Java Keywords
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
super
switch
synchronized
this
throw
throws
transient
try
void
volatile
while
Operator
**Sama seperti dalam C
 Operator dasar:
◦ +, -, /, *, %

Contoh:
◦ bil += 5; setara dengan bil = bil + 5;

(++ dan –-)
◦ Contoh:
int i= 1;
int x = 5 - ++i;
//nilai x menjadi 3
//nilai i menjadi 2
Hubungan
**Sama seperti dalam C
 Operator dasar:
◦ ==, !=, <, >, <=, >=

Apa bedanya?
◦ bil = 0;
◦ if(bil == 0)
Operator logik
**Sama seperti dalam C
 Operator dasar:
◦ &&
◦ ||
◦!
:
:
:
DAN
ATAU
BUKAN
Common Java Operators / Operator
Precedence
Precedence
level
Operator
1
expression++ Post-increment
expression--
2
Description
Associativity
Right to left
Post-decrement
++expression Pre-increment
--expression
Pre-decrement
+
Unary plus
-
Unary minus
!
Logical negation
~
Bitwise complement
(type)
Cast
Right to left
Common Java Operators / Operator
Precedence
Precedence
level
Operator
Description
Associativity
3
*
Multiplication
Left to right
/
Division
%
Remainder/modulus
+
Addition or String
concatenation
-
Subtraction
<<
Left bitwise shift
>>
Right bitwise shift
4
5
Left to right
Left to right
Common Java Operators / Operator
Precedence
Precedence Operator
level
Description
Associativity
6
<
Less than
Left to right
<=
Less than, equal to
>
Greater than
>=
Greater than, equal to
==
Equal to
!=
Not equal to
8
&
Bitwise AND
Left to right
9
^
Bitwise exclusive OR
Left to right
7
Left to right
Common Java Operators / Operator
Precedence
Precedence Operator
level
Description
Associativity
10
|
Bitwise OR
Left to right
11
&&
Logical AND
Left to right
12
||
Logical OR
Left to right
Common Java Operators / Operator
Precedence
Precedence Operator
level
Description
Associativity
13
=
Assignment
Right to left
+=
Add, assignment
-=
Subtract, assignment
*=
Multiply, assignment
/=
Division, assignment
%=
Remainder, assignment
&=
Bitwise AND, assignment
^=
Bitwise XOR, assignment
|=
Bitwise OR, assignment
<<=
Left shift, assignment
>>=
Right shift, assignment
Post/Pre Operators
The name of the example is: Order1.java
public class Order1
{
public static void main (String [] args)
{
int num = 5;
System.out.println(num);
num++;
System.out.println(num);
++num;
System.out.println(num);
System.out.println(++num);
System.out.println(num++);
}
}
Post/Pre Operators (2)
The name of the example is: Order2.java
public class Order2
{
public static void main (String [] args)
{
int num1;
int num2;
num1 = 5;
num2 = ++num1 * num1++;
System.out.println("num1=" + num1);
System.out.println("num2=" + num2);
}
}
Unary Operator/Order/Associativity
The name of the example: Unary_Order3.java
public class Unary_Order3.java
{
public static void main (String [] args)
{
int num = 5;
float fl;
System.out.println(num);
num = num * -num;
System.out.println(num);
}
}
Accessing Pre-Created Java Libraries
It’s accomplished by placing an ‘import’ of
the appropriate library at the top of your
program.
 Syntax:

import <Full library name>;

Example:
import java.util.Scanner;
Getting Text Input


You can use the pre-written methods (functions) in the
Scanner class.
General structure:
import java.util.Scanner;
main (String [] args)
{
Scanner <name of scanner> = new Scanner (System.in);
<variable> = <name of scanner> .<method> ();
}
Creating a
scanner object
(something
that can scan
user input)
Using the capability of
the scanner object
(actually getting user
input)
Getting Text Input (2)
The name of the example: MyInput.java
import java.util.Scanner;
public class MyInput
{
public static void main (String [] args)
{
String str1;
int num1;
Scanner in = new Scanner (System.in);
System.out.print ("Type in an integer: ");
num1 = in.nextInt ();
System.out.print ("Type in a line: ");
in.nextLine ();
str1 = in.nextLine ();
System.out.println ("num1:" +num1 +"\t str1:" + str1);
}
}
Useful Methods Of Class Scanner1





nextInt ()
nextLong ()
nextFloat ()
nextDouble ()
nextLine ();
1 Online documentation: docs.oracle.com/javase/7/docs/api/
Reading A Single Character
Text menu driven programs may require this
capability.
 Example:

GAME OPTIONS
(a)dd a new player
(l)oad a saved game
(s)ave game
(q)uit game
There’s different ways of handling this problem
but one approach is to extract the first character
from the string.
 Partial example:

String s = "boo“;
System.out.println(s.charAt(0));
Reading A Single Character

Name of the (more complete example):
MyInputChar.java
import java.util.Scanner;
public class MyInputChar
{
public static void main (String [] args)
{
final int FIRST = 0;
String selection;
Scanner in = new Scanner (System.in);
System.out.println("GAME OPTIONS");
System.out.println("(a)dd a new player");
System.out.println("(l)oad a saved game");
System.out.println("(s)ave game");
System.out.println("(q)uit game");
System.out.print("Enter your selection: ");
Reading A Single Character (2)
selection = in.nextLine ();
System.out.println ("Selection: " + selection.charAt(FIRST));
}
}
Decision Making In Java

Java decision making constructs
◦
◦
◦
◦
if
if, else
if, else-if
switch
Decision Making: Logical Operators
Logical Operation
Java
AND
&&
OR
||
NOT
!
Decision Making: If
Format:
if (Boolean Expression)
Body
Example:
if (x != y)
System.out.println("X and Y are not equal");
if ((x > 0) && (y > 0))
{
System.out.println("X and Y are positive");
}
• Indenting the body
of the branch is an
important stylistic
requirement of Java.
• What distinguishes
the body is either:
1.A semi colon
(single statement
branch)
2.Braces (a body
that consists of
multiple
statements)
Decision Making: If, Else
Format:
if (Boolean expression)
Body of if
else
Body of else
Example:
if (x < 0)
System.out.println("X is negative");
else
System.out.println("X is non-negative");
Example Program: If-Else

Name of the example: BranchingExample1.java
import java.util.Scanner;
public class BranchingExample1
{
public static void main (String [] args)
{
Scanner in = new Scanner(System.in);
final int WINNING_NUMBER = 131313;
int playerNumber = -1;
System.out.print("Enter ticket number: ");
playerNumber = in.nextInt();
if (playerNumber == WINNING_NUMBER)
System.out.println("You're a winner!");
else
System.out.println("Try again.");
}
}
If, Else-If
Format:
if (Boolean expression)
Body of if
else if (Boolean expression)
Body of first else-if
:
:
:
else if (Boolean expression)
Body of last else-if
else
Body of else
If, Else-If (2)
Name of the example: BranchingExample.java
import java.util.Scanner;
public class BranchingExample2
{
public static void main (String [] args)
{
Scanner in = new Scanner(System.in);
int gpa = -1;
System.out.print("Enter letter grade: ");
gpa = in.nextInt();
If, Else-If (3)
if (gpa == 4)
System.out.println("A");
else if (gpa == 3)
System.out.println("B");
else if (gpa == 2)
System.out.println("C");
else if (gpa == 1)
System.out.println("D");
else if (gpa == 0)
System.out.println("F");
else
System.out.println("Invalid letter grade");
}
}
Branching: Common Mistakes

Recall that for single bodies: what lies between the
closing bracket of the Boolean expression and the next
semi-colon is the body.
if (Boolean Expression)
instruction;
body
body
if (Boolean Expression) instruction;
if (Boolean Expression)
body
instruction1;
Instruction2;
Branching: Now What Happens???
if (Boolean Expression):
instruction1;
instruction2;
Alternative To Multiple Else-If’s:
Switch
Format (character-based switch):
switch (character variable name)
{
case '<character value>':
Body
break;
Important! The break is
mandatory to separate
Boolean expressions
(must be used in all but
the last)
case '<character value>':
Body
break;
:
default:
Body
}
1 The type of variable in the brackets can be a byte, char, short, int or long
Alternative To Multiple Else-If’s:
Switch (2)
Format (integer based switch):
switch (integer variable name)
{
case <integer value>:
Body
break;
case <integer value>:
Body
break;
:
default:
Body
}
1 The type of variable in the brackets can be a byte, char, short, int or long
Switch: When To Use/When Not To
Use

Benefit (when to use):
◦ It may produce simpler code than using an ifelseif (e.g., if there are multiple compound
conditions)
Switch: When To Use/When Not To
Use (2)

Name of the example: SwitchExample.java
import java.util.Scanner;
public class SwitchExample
{
public static void main (String [] args)
{
final int FIRST = 0;
String line;
char letter;
int gpa;
Scanner in = new Scanner (System.in);
System.out.print("Enter letter grade: ");
Switch: When To Use/When Not To
Use (3)
line = in.nextLine ();
letter = line.charAt(FIRST);
switch (letter)
{
case 'A':
case 'a':
gpa = 4;
break;
case 'B':
case 'b':
gpa = 3;
break;
case 'C':
case 'c':
gpa = 2;
break;
Switch: When To Use/When Not To
Use (4)
case 'D':
case 'd':
gpa = 1;
break;
case 'F':
case 'f':
gpa = 0;
break;
default:
gpa = -1;
}
System.out.println("Letter grade: " + letter);
System.out.println("Grade point: " + gpa);
}
}
Switch: When To Use/When Not To
Use (5)

When a switch can’t be used:
◦ For data types other than characters or integers
◦ Boolean expressions that aren’t mutually exclusive:
 As shown a switch can replace an ‘if-elseif’ construct
 A switch cannot replace a series of ‘if’ branches).
◦ Example when not to use a switch:
if (x > 0)
System.out.print(“X coordinate right of the origin”);
If (y > 0)
System.out.print(“Y coordinate above the origin”);
◦ Example of when not to use a switch:
String name = in.readLine()
switch (name)
{
}
Switch Example: Modified

What happens if all the ‘break’ instructions
have been removed?
STRUKTUR KAWALAN

STRUKTUR PEMILIHAN
◦ if-else
◦ switch-break

STRUKTUR PENGULANGAN
◦ while
◦ do-while
◦ for
STRUKTUR PEMILIHAN

if-else
if (ungkapan)
kenyataan
◦ Contoh:
if (skorPelajar >= 60)
System.out.println(“LULUS”);
◦ Sintaksnya sama dengan C, kecuali dalam Java, ungkapan
mesti bernilai boolean (true or false).
◦ Oleh itu penggalan berikut tidak dibenarkan dalam Java:
int bilangan =10;
if(bilangan)
System.out.print(“*”);
STRUKTUR PEMILIHAN

switch-case
**sintaksnya sama seperti C
◦ Hanya boleh jenis integer dan aksara: byte, char, short, int
atau long
int pilihan =1;
switch(pilihan){
case 1: …
break;
case 2: ..
break;
default: …
break;
}
STRUKTUR PENGULANGAN

while, do-while dan for
**sintaksnya sama seperti C
◦ Buatkan program Java dengan menggunakan
while dan do-while bagi pseudokod di bawah:
lapar = benar
Selagi lapar benar
tampilkan “beri makanan”
lapar = false
Tamat selagi
Loops
Java Pre-test loops
• For
• While
Java Post-test loop
• Do-while
While Loops
Format:
while (Boolean expression)
Body
Example:
int i = 1;
while (i <= 4)
{
// Call function
createNewPlayer();
i = i + 1;
}
For Loops
Format:
for (initialization; Boolean expression; update control)
Body
Example:
for (i = 1; i <= 4; i++)
{
// Call function
createNewPlayer();
i = i + 1;
}
Post-Test Loop: Do-While
Recall: Post-test loops evaluate the
Boolean expression after the body of the
loop has executed.
 This means that post test loops will
execute one or more times.
 Pre-test loops generally execute zero or
more times.

Do-While Loops
Format:
do
Body
while (Boolean expression);
Example:
char ch = 'A';
do
{
System.out.println(ch);
ch++;
}
while (ch <= 'K');
Contrasting Pre Vs. Post Test Loops



Although slightly more work to implement
the while loop is the most powerful type of
loop.
Program capabilities that are implemented
with either a ‘for’ or ‘do-while’ loop can be
implemented with a while loop.
Implementing a post test loop requires that
the loop control be primed correctly (set to
a value such that the Boolean expression will
evaluate to true the first it’s checked).
Example: Post-Test Implementation

Name of the example: PostTestExample.java
public class PostTestExample
{
public static void main (String [] args)
{
final int FIRST = 0;
Scanner in = new Scanner(System.in);
char answer;
String temp;
do
{
System.out.println("JT's note: Pretend that we play our game");
System.out.print("Play again? Enter 'q' to quit: ");
temp = in.nextLine();
answer = temp.charAt(FIRST);
} while ((answer != 'q') && (answer != 'Q'));
}
}
Example: Pre-Test Implementation

Name of the example: PreTestExample.java
public class PreTestExample
{
public static void main (String [] args)
{
final int FIRST = 0;
Scanner in = new Scanner(System.in);
char answer = ' ';
String temp;
while ((answer != 'q') && (answer != 'Q'))
{
System.out.println("JT's note: Pretend that we play our game");
System.out.print("Play again? Enter 'q' to quit: ");
temp = in.nextLine();
answer = temp.charAt(FIRST);
}
}
}
Now What Happens???
import java.util.Scanner;
public class PreTestExample
{
public static void main (String [] args)
{
final int FIRST = 0;
Scanner in = new Scanner(System.in);
char answer = ' ';
String temp;
while ((answer != 'q') && (answer != 'Q'))
System.out.println("JT's note: Pretend that we play our game");
System.out.print("Play again? Enter 'q' to quit: ");
temp = in.nextLine();
answer = temp.charAt(FIRST);
}
}
Array

Sintaks
◦ Tipe_data[] nama_variable = new
tipe_data[ukuran];

Contoh:
int[] tts = new int[100];
int[] tts;
tts = new int[100];
int tts[]= new int[100];
ATAU
ATAU
Array (2)

Memberi nilai kepada array:
int[] nilai = {2, 3, 4, 5};
char[] abjad= {a, b, c, d};

Kita juga bisa membuat array tanpa nama:
new int[]{2, 3, 5, 7, 11};
menyediakan satu array baru dengan
nilai-nilai tersebut. Sering dipakai untuk mengirim parameter
ke method.
Array (3)

Digunakan apabila kita ingin mengirimkan
array sebagai parameter pada method.
cetakLimaPrima(new int[] {2,3,5,7,11} );
ATAU
int[] nomPrima = {2,3,5,7,11};
cetakLimaPrima(nomPrima);
Array Sebagai Objek
Apabila ia dianggap sebagai objek, maka ia
mempunyai atribut dan method
 Atribut length

◦ Menentukan ukuran suatu array:
nama_array.length
int nomPrima={2, 3, 5, 7, 11};
for(int i=0; i<nomPrima.length;i++)
System.out.println(nomPrima[i]);

Method arraycopy()
◦ Mengcopy dari satu array ke array yang lain.
Sintaksnya:
◦ System.arraycopy(sumber,indekSumber,sasaran,
indekSasaran,bil);
sumber :nama array yang hendak dicopy
indekSumber :permulaan kedudukan array yang akan di copy dari sumber
sasaran : array baru yang akan menyimpan
kandungan array sumber
indekSasaran :permulaan kedudukan pada array
sasaran untuk menyimpan nilai yang dicopy
bil
:
jumlah nilai yang dicopy
Metod arraycopy()
int[] nomGanjil ={1, 3, 5, 7, 9};
int[] nomPositif={10, 20, 30, 40, 50, 60};
System.arraycopy(nomGanjil, 1, nomPositif, 2, 3);
for(int i=0; i<nomPositif.length; i++){
Sysem.out.println(“nomPositif[“ + i + “] selepas copy:”
+nomPositif[i]);
}
OUTPUT
nomPositif[0] selepas copy ialah 10
nomPositif[1] selepas copy ialah 20
nomPositif[2] selepas copy ialah 3
nomPositif[3] selepas copy ialah 5
nomPositif[4] selepas copy ialah 7
nomPositif[5] selepas copy ialah 60
System.arraycopy(nomGanjil, 1, nomPositif, 2, 3);
Sebelum copy
1
10
3
20
5
30
7
40
9
50
60
Selepas copy
1
10
3
20
5
3
7
5
9
7
60
String
Berbeda dengan C, Java mempunyai kelas String.
Kita tidak perlu tipe data array char untuk
menyimpan rentetan aksara.
 Tipe data berjenis String akan menyimpan aksara di
antara tanda “ “, termasuk ruang kosong


◦ Contoh: String kosong=“”; //suatu rentetan kosong
◦ String namaSaya = “Mohammad Muktasim”;
Operasi Terhadap String

Menggabung string
◦ Menggunakan operator ‘+’
String judul = “OO”;
String buku = “.Java”;
String judulBuku = judul + buku;
System.out.println(judulBuku);
OUTPUT
OO.Java
//tanpa spasi
Operasi Terhadap String
Java mengira subrentetan
bermula dari 0 hingga 4
0: kedudukan ‘P’
 Substring
4: kedudukan ‘i’
◦ Mendapatkan sebahagian daripada string yang lengkap
◦ Metod substring() digunakan
String senikata = “Puji dan syukur kepada Ilahi”;
String s = senikata.substring(0,4);
System.out.println(“Subrentetan bernilai ”+s);
OUTPUT
Subrentetan bernilai Puji
Operasi Terhadap String

Panjang string
◦ Mendapatkan panjang suatu string
◦ Metod length() digunakan
String kata = “Salam Sejahtera”;
int panjang = kata.length();
// panjang bernilai 15

Membanding string
◦ Menguji apakah dua string mempunyai nilai yang sama
◦ Metod equals() digunakan
“salam”.equals(kata);
// bernilai false
“Salam sejahtera”.equalIgnoreCase(kata);
// bernilai true
Method parser

Contoh: weight = Integer.parseInt(kilo);
Nilai yang berjenis String yang disimpan dalam kilo akan
ditukar menjadi integer dan disimpan dalam weight

Jenis parser yang lain:
◦ parseInt(), parseFloat(), parseLong(),
parseDouble, parseShort(), parseByte().
Many Pre-Created Classes Have
Been Created
Rule of thumb: Before writing new
program code to implement the features
of your program you should check to see
if a class has already been written with
the features that you need.
 The Java API is Sun Microsystems's
collection of pre-built Java classes:

◦ http:// docs.oracle.com/javase/7/docs/api/
I hear, I forget
I write, I remember
I do, I understand..
so..
just do it!
:-)
Supplemental reading

Getting Started
http://java.sun.com/docs/books/tutorial/getStarted/index.html

Nuts and bolts of the Java Language
http://java.sun.com/docs/books/tutorial/java/nutsandbolts/index.html

Compiling and Running a Simple Program
http://developer.java.sun.com/developer/onlineTraining/Programming/BasicJ
ava1/compile.html