1. Chapter 3 : Basic Concept Of Java
Prepared By Madam Zanariah Idrus

2. CONTENT Identifiers in Java Data types Wrapper classes
The ‘+’ operator
How to design main class
Control structures

3. Identifiers in Java
An identifier is a sequence of characters that can be used to name entities such as variables, methods, classes and packages in a java program.
Rules for naming identifiers in java:
must start with an alphabet or the underscore symbol.
the remaining characters must be letters, digit, or the underscore symbol.
spaces and other special characters are not permitted.
keywords are also not allowed to be used as identifiers.
identifiers are also case-sensitive, that is Number and NumBer are treated as two different identifiers.
Examples:
MySalaryRM
Number19
computeDiscount

4. Data Types There are two categories of data types which are:
Primitive data types
Predefined class

5. Primitive Data type Primitive data types
When writing programs we need to specify the data types that we are working with.
Examples java primitive data types are:
int, double, float, char and boolean.

6. Predefined Class Predefined class
Predefined class is the class that provide by Java program.
String data type is not a primitive data type in Java.
A string is sequence of character enclosed by the double quotes (“ “).
Java provides the String class, the StringBuffer class and StringTokenizer class for storing and processing strings.
Examples creating a string:
String message= “Welcome to UiTM!”;
String message= new String (“Welcome to UiTM!”);

7. Intro to OOP with Java, C. Thomas Wu
Characters
In Java, single characters are represented using the data type char.
Character constants are written as symbols enclosed in single quotes.
Characters are stored in a computer memory using some form of encoding.
ASCII, which stands for American Standard Code for Information Interchange, is one of the document coding schemes widely used today.
Java uses Unicode, which includes ASCII, for representing char constants.
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8. Intro to OOP with Java, C. Thomas Wu
ASCII Encoding
For example, character 'O' is 79 (row value 70 + col value 9 = 79). O 9 70
Characters can be stored in a computer memory using the ASCII encoding. The ASCII codes range from 0 to 127. The character 'A' is represented as 65, for example. The ASCII values from 0 to 32 are called nonprintable control characters. For example, ASCII code 04 eot stands for End of Transmission. We can use this character to signal the end of transmission of data when sending data over a communication line.
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9. Intro to OOP with Java, C. Thomas Wu
Unicode Encoding
The Unicode Worldwide Character Standard (Unicode) supports the interchange, processing, and display of the written texts of diverse languages.
Java uses the Unicode standard for representing char constants.
char ch1 = 'X';
System.out.println(ch1);
System.out.println( (int) ch1);
ASCII works well for English-language documents because all characters and punctuation marks are included in the ASCII codes. But ASCII codes cannot be used to represent character sets of other languages. To overcome this limitation, unicode encoding was proposed. Unicode uses two bytes to represent characters and adopts the same encoding for the first 127 values as the ASCII codes.
Encoding value of a character can be accessed by converting it to an int as the sample code illustrates. X 88
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10. Intro to OOP with Java, C. Thomas Wu
Character Processing
Declaration and initialization
char ch1, ch2 = ‘X’;
Type conversion between int and char.
System.out.print("ASCII code of character X is " + (int) 'X' );
System.out.print("Character with ASCII code 88 is " + (char)88 );
This comparison returns true because ASCII value of 'A' is 65 while that of 'c' is 99.
‘A’ < ‘c’
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11. Intro to OOP with Java, C. Thomas Wu
Strings
A string is a sequence of characters that is treated as a single value.
Instances of the String class are used to represent strings in Java.
We can access individual characters of a string by calling the charAt method of the String object.
We introduced the String class in Chapter 2. We will study additional String methods.
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12. Accessing Individual Elements
Intro to OOP with Java, C. Thomas Wu
Accessing Individual Elements
Individual characters in a String accessed with the charAt method.
String name = "Sumatra"; 1 2 3 4 5 6 S u m a t r
name
This variable refers to the whole string.
name.charAt( 3 )
The method returns the character at position # 3.
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13. Example: Counting Vowels
Intro to OOP with Java, C. Thomas Wu
Example: Counting Vowels
char letter;
String name = JOptionPane.showInputDialog(null,"Your name:");
int numberOfCharacters = name.length();
int vowelCount = 0;
for (int i = 0; i < numberOfCharacters; i++) {
letter = name.charAt(i);
if ( letter == 'a' || letter == 'A' ||
letter == 'e' || letter == 'E' ||
letter == 'i' || letter == 'I' ||
letter == 'o' || letter == 'O' ||
letter == 'u' || letter == 'U' ) {
vowelCount++; }
System.out.print(name + ", your name has " + vowelCount + " vowels");
Here’s the code to count the number of vowels in the input string.
This sample code counts the number of vowels in a given input.
Using the toUpperCase method, that converts all alphabetic characters to uppercase, we can rewrite the code as
char letter;
String name = inputBox.getString("What is your name?");
int numberOfCharacters = name.length();
int vowelCount = 0;
String nameUpper = name.toUpperCase();
for (int i = 0; i < numberOfCharacters; i++) {
letter = nameUpper.charAt(i);
if ( letter == 'A' ||
letter == 'E' ||
letter == 'I' ||
letter == 'O' ||
letter == 'U' ) {
vowelCount++; }
System.out.print(name + ", your name has " + vowelCount + " vowels");
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14. Example: Counting ‘Java’
Intro to OOP with Java, C. Thomas Wu
Example: Counting ‘Java’
int javaCount = 0;
boolean repeat = true;
String word;
while ( repeat ) {
word = JOptionPane.showInputDialog(null,"Next word:");
if ( word.equals("STOP") ) {
repeat = false;
} else if ( word.equalsIgnoreCase("Java") ) {
javaCount++; }
Continue reading words and count how many times the word Java occurs in the input, ignoring the case.
Notice how the comparison is done. We are not using the == operator.
This sample code counts the number of times the word 'Java' is entered.
Notice that we wrote
word.equals( “STOP”)
not
word == “STOP”
We described the differences in Lesson 5-2. In this situation, we need to use 'equals' because we are testing whether two String objects have the same sequence of characters.
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15. Other Useful String Operators
Intro to OOP with Java, C. Thomas Wu
Other Useful String Operators
Method
Meaning
compareTo
Compares the two strings. str1.compareTo( str2 )
substring
Extracts the a substring from a string. str1.substring( 1, 4 )
trim
Removes the leading and trailing spaces. str1.trim( )
valueOf
Converts a given primitive data value to a string. String.valueOf( )
startsWith
Returns true if a string starts with a specified prefix string. str1.startsWith( str2 )
endsWith
Returns true if a string ends with a specified suffix string. str1.endsWith( str2 )
Here are some examples:
String str1 = “Java”, str2 = “ Wow “;
str1.compareTo( “Hello” ); //returns positive integer
//because str1 >= “Hello”
str1.substring( 1, 4 ); //returns “ava”
str2.trim( ) //returns “Wow”, str2 stays same
str1.startsWith( “Ja” ); //returns true
str1.endsWith( “avi” ); //returns false
See the String class documentation for details.
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16. Intro to OOP with Java, C. Thomas Wu
Pattern Example
Suppose students are assigned a three-digit code:
The first digit represents the major (5 indicates computer science);
The second digit represents either in-state (1), out-of-state (2), or foreign (3);
The third digit indicates campus housing:
On-campus dorms are numbered 1-7.
Students living off-campus are represented by the digit 8.
The 3-digit pattern to represent computer science majors living on-campus is
We can use a pattern to represent a range of valid codes succintly. Without using the sample 3-digit pattern for computer science majors living on-campus, we must spell out 21 separate codes.
5[123][1-7]
first
character
is 5
second
character
is 1, 2, or 3
third
character
is any digit
between 1 and 7
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17. Intro to OOP with Java, C. Thomas Wu
Regular Expressions
The pattern is called a regular expression.
Rules
The brackets [ ] represent choices
The asterisk symbol * means zero or more occurrences.
The plus symbol + means one or more occurrences.
The hat symbol ^ means negation.
The hyphen – means ranges.
The parentheses ( ) and the vertical bar | mean a range of choices for multiple characters.
Regular expression allows us to express a large set of “words” (any sequence of symbols) succinctly. We use specially designated symbols such as the asterisk to formulate regular expressions.
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18. Regular Expression Examples
Intro to OOP with Java, C. Thomas Wu
Regular Expression Examples
Expression
Description
[013]
A single digit 0, 1, or 3.
[0-9][0-9]
Any two-digit number from 00 to 99.
[0-9&&[^4567]]
A single digit that is 0, 1, 2, 3, 8, or 9.
[a-z0-9]
A single character that is either a lowercase letter or a digit.
[a-zA-z][a-zA-Z0-9_$]*
A valid Java identifier consisting of alphanumeric characters, underscores, and dollar signs, with the first character being an alphabet.
[wb](ad|eed)
Matches wad, weed, bad, and beed.
(AZ|CA|CO)[0-9][0-9]
Matches AZxx,CAxx, and COxx, where x is a single digit.
Here are some examples of regular expressions.
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19. Data Types Predefined class Some method in the class String
Method Name
Description 1
int length( )
Return the length of string
message.length( ) return 16 2
charAt(index)
Return the character at a particular index in a string.
Note that the index of first character is 0.
message.charAt(0)  returns the letter W
message.charAt(11)  returns the letter U 3
substring (startIndex)
Gets more than one consecutive character from a string.
Returns a new string begins at the specified startindex until the end of the string.
substring(11)  returns the string UiTM 4
substring(startIndex, endIndex)
Returns a new string begins at the specified startindex until the character at index endindex -1
substring(11,15)  returns the string UiTM

20. Data Types Predefined class Some method in the class String
Method Name
Description 5
equals(String2)
Returns true if the calling object and string2 are identical, otherwisw returns false.
String greeting1=“Hai”;
String greeting2= “Hello”;
greeting1.equals(greeting2) returns false
greeting1.equals(“Hai”) returns true
greeting1.equals(“HAi”) returns false 6
equalsIgnoreCase (String2)
Returns true if the calling object is equal (ignoring whether the characters are lower case or uppercase).
greeting1.equalsIgnoreCase(“HAI”) returns true

21. Data Types Predefined class Some method in the class String
Method Name
Description 7
toLowerCase()
Converts and returns all the characters in the string to lower case letter.
message.toLowerCase() returns welcome to uitm 8
toUpperCase()
Converts and returns all the characters in the string to upper case letter.
message.toLowerCase() returns WELCOME TO UITM

22. Predefined class Usage Package Method Example Dialog Box javax.swing
showInputDialog(String)
showMessageDialog(String)
String w = JOptionPane.showInputDialog(null, “Enter name”);
showMessageDialog(null, “Good Morning!”);
Format output
java.text
class name = DecimalFormat
format(String)
DecimalFormat n = new DecimalFormat(“00.00”)
To diplay decimal placeholder
Mathematical Methods
Static methods in class Math are used.
abs(n)
pow(n1, n2)
sqrt(n1)
round(n)
min(x, y)
int x = Math.pow(4,2);

23. Example:

24. Intro to OOP with Java, C. Thomas Wu
The replaceAll Method
The replaceAll method replaces all occurrences of a substring that matches a given regular expression with a given replacement string.
Replace all vowels with the
String originalText, modifiedText;
originalText = ...; //assign string
modifiedText =
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25. The StringBuffer Class
Intro to OOP with Java, C. Thomas Wu
The StringBuffer Class
In many string processing applications, we would like to change the contents of a string. In other words, we want it to be mutable /changeable.
Manipulating the content of a string, such as replacing a character, appending a string with another string, deleting a portion of a string, and so on, may be accomplished by using the StringBuffer class.
If the situation calls for directing changing the contents of a string, then we use the StringBuffer class.
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26. Intro to OOP with Java, C. Thomas Wu
StringBuffer Example
word
: StringBuffer
Java
Before
word
: StringBuffer
Diva
After
Changing a string Java to Diva
This sample code illustrates how the original string is changed. Notice that the String class does not include the setCharAt method. The method is only defined in the mutable StringBuffer class.
StringBuffer word = new StringBuffer("Java");
word.setCharAt(0, 'D');
word.setCharAt(1, 'i');
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27. Intro to OOP with Java, C. Thomas Wu
Sample Processing
char letter;
String inSentence = JOptionPane.showInputDialog(null, "Sentence:");
StringBuffer tempStringBuffer = new StringBuffer(inSentence);
int numberOfCharacters = tempStringBuffer.length();
for (int index = 0; index < numberOfCharacters; index++) {
letter = tempStringBuffer.charAt(index);
if ( letter == 'a' || letter == 'A' || letter == 'e' || letter == 'E' ||
letter == 'i' || letter == 'I' || letter == 'o' || letter == 'O' ||
letter == 'u' || letter == 'U' ) {
tempStringBuffer.setCharAt(index,'X'); }
JOptionPane.showMessageDialog(null, tempStringBuffer );
Replace all vowels in the sentence with ‘X’.
Notice how the input routine is done. We are reading in a String object and converting it to a StringBuffer object, because we cannot simply assign a String object to a StringBuffer variable.
For example, the following code is invalid:
StringBuffer strBuffer = inputBox.getString( );
We are required to create a StringBuffer object from a String object as in
String str = "Hello";
StringBuffer strBuf = new StringBuffer( str );
You cannot input StringBuffer objects. You have to input String objects and convert them to StringBuffer objects.
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28. Wrapper Classes
Java provides routine for converting String to a primitive data types or vice versa
It is called wrapper classes because the classes constructed by wrapping a class structure around the primitive data types

29. Wrapper Classes Wrapper Class Method Description Example Integer
parseInt(String)
Converts a string to int
int x = Integer.parseInt(s);
toString(x)
Converts an int to string
String s = Integer.toString(x);
Long
parseLong(string)
Converts a string to long int
Long x = Long.parseLong(s);
Converts a long int to string
String s = Long.toString(x);
Float
parseFloat(s)
Converts a string to float
float x = Float.parseFloat(s);
Converts a float to string
String s = Float.toString(x);
Double
parseDouble(s)
Converts a string to double
double x = Double.parseDouble(s);
Converts a double to string
String s = Double.toString(x);

30. Wrapper Classes

31. The “+” Operator
The + operator denotes concatenation when used with Strings.
Examples:
String string1 = “Hello”;
String string2= “Students”;
The statement string1 + string2  Hello Students
If one of the operands is a String, the other is not, then the non-string operand will be converted to a String.
int integer1 = 122;
string2 + integer1  “Students122”
integer1 + string2  “122Students”
“$” integer1  “$3122”

32. How to design main class
Design main/ application class
Step 1: Define import statement package.
The import statement package contains classes that perform input and output process.
There are three import statements package that you can choose:
import java.io.*; // for bufferedReader package
import javax.swing.JOptionPane; //for GUI (pop up) interface
import java.util.Scanner; // for Scanner package OR OR

33. How to design main class
Design main/ application class
Step 2: Define main class name
public class mainApp( you can choose your own name) {
Step 3: Define main method
public static void main ( String args [ ])
If you choose bufferedReader package for your input/output process, your main method must required to handle/throw the IOException:
Examples: public static void main ( String args [ ]) throws IOException

34. How to design main class
Design main/ application class
Step 4: Declare variable to hold input data
String insert
Step 5: Create object if you used bufferedReader or Scanner package
BufferedReader package
BufferedReader input = new BufferedReader ( new InputStreamReader ( System.in));
Scanner package
Scanner sc = new Scanner ( System.in);

35. How to design main class
Design main/ application class
Step 6: Input statement. If you choose:
BufferedReader
System.out.print(“Enter num 1: ”)
//hold the input line
insert = input. readLine( ); //read first line
//data conversion
num1= Integer.parseInt (insert);
System.out.print(“Enter num 2: ”)
num2= Integer.parseInt (insert);

36. How to design main class
Design main/ application class
Step 6: Input statement. If you choose:
JOptionPane
insert= JOptionPane.showInputDialog (“Enter num1: ”);
num1= Integer.parseInt(insert);
insert= JOptionPane.showInputDialog (“Enter num2: ”);
num2= Integer.parseInt(insert);
Scanner
System.out.print(“Enter num1:”);
num1= sc.nextInt( );
System.out.print(“Enter num2:”);
num2= sc.nextInt( );

37. How to design main class
Design main/ application class
Step 7: Process/calculation
total = num1 + num2;
Step 8: Output statement. If you choose:
BufferedReader OR Scanner
System.out.println (num1 + “+” + num2 + “=“ + total);
JOptionPane
JOptionPane.showMessageDialog( null, num1 + “ +” num2 + “=“ + total);

38. How to design main class

39. Example main class definition
BufferedReader package

40. Example main class definition
JOptionPane package

41. Example main class definition
Scanner package

42. Control Structures There are three control structures 1. Sequence
Program start from the left to right, top to bottom statements in main ( ).
2. Selection/decision
Program will carry out different actions depending on the nature of the inputs (condition).
One-way, two-ways and multiple-ways.
Including switch-case ( round number and character only).
3. Repetition/iteration
Program will repeatedly execute one or more statements while the condition is true.
Three types of repetition  while loop, do..while loop and for loop.

43. Control Structures

44. Examples of using control structures

45. Example program selection

46. Example program selection (switch)

47. Example program selection (switch)

48. Example program repetition

49. THE END