1. Review Java

2. Objectives
To understand the essentials of object- oriented programming in Java
To review the primitive data types of Java, how to use the control structures of Java
To learn how to use predefined classes such as Math, JOptionPane, String, StringBuffer, and StringTokenizer
To review how to write and document your own Java classes
Appendix A: Introduction to Java

3. Chapter Objectives (continued)
To understand how to use arrays in Java
To learn how to perform I/O in Java using simple dialog windows
To learn how to perform I/O in Java using streams
Appendix A: Introduction to Java

4. Compiling and Executing a Java Program
Appendix A: Introduction to Java

5. Classes and Objects The class is the fundamental programming unit
Every program is written as a collection of classes
Class definitions are stored in separate files with the extension .java and the file name must be the same as the class name
A class is a named description for a group of entities
A class is a general description of a group of entities that all have the same characteristics; each entity is an object
Appendix A: Introduction to Java

6. The Java API
Java consists of small core language augmented by an extensive collection of packages
Each package contains a collection of related Java classes, such as:
Swing
AWT
util
Appendix A: Introduction to Java

7. Review of Java fundamentals
Template for Class Definition
class { }
Import Statements
Class Comment
Class Name
Data Members
Methods
(incl. Constructor)

8. Primitive Data Types and Reference Variables
Java distinguishes two kinds of entities
Primitive types: data is stored in primitive type variables
Objects: are associated with reference variables which store an object’s address
Appendix A: Introduction to Java

9. Primitive Data Types Represent numbers, characters, and Boolean values
Integers: byte, short, int, and long
Real numbers: float and double
Characters: char
Appendix A: Introduction to Java

10. 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.

11. Variable declaration
Format: <data type> <variable_name>; If more than one variable has the same data type: <data type> <name1>, <name2>..;

12. Assignment statement
<variable name> = <expression>; Example: x =2*5+6-1;

13. Variable names It must be a legal identifier.
It must not be a keyword, a boolean literal (true or false), or the reserved word null.
It must be unique within its scope.

14. Variable name (cont.)
Legal identifier:be composed of letters, numbers, _ and $. Identifiers may only begin with a letter, _, or $.
Keyword:
nutsandbolts/_keywords.html
Java styles:
Variable names begin with a lowercase letter
Class names begin with an uppercase letter

15. Review question Which of the following is not a valid Java identifier?
a. my Value
b. $_AAA1
c. width
d. m_x
Appendix A: Introduction to Java

16. Review question Which of the following is not a valid Java identifier?
a. my Value
b. $_AAA1
c. width
d. m_x
Appendix A: Introduction to Java

17. Review question
Which of the following is a correct variable declaration statement?
a. int x - float y;
b. int x: float y;
c. int x,y;
d. Long int x;
Appendix A: Introduction to Java

18. Review question
Which of the following is a correct variable declaration statement?
a. int x - float y;
b. int x: float y;
c. int x,y;
d. Long int x;
Appendix A: Introduction to Java

19. Constant and variables
Value it contains doesn’t change
final int MONTHS_IN_YEAR = 12;
Variables:
Value it contains may vary
double loanAmount;
loanAmount =0;
loanAmount = ;

20. Integer division and type casting
Integer/integer = integer, 7/2 = 3
Integer/double = double, 7/2.0 = 3.5
Double/integer = double, 7.0/2 = 3.5
Type casting: a process that converts a value of one data type to another data type. Implicit casting
Explicit casting

21. Type casting (cont.) Implicit casting:
Operand is converted from a lower to a higher precision
Higher precision: a data type with a larger range of values
Double has a higher precision than float
Int has a higher precision than short
Operand: can be a constant, variable, method call or another arithmetic expression

22. Type casting (cont.) Explicit casting
(<data type>) <expression>
Example:
float result;
result = (float) ((3+5)/6);
and
result = ((float) (5+3))/6;

23. Type Compatibility and Conversion
Widening conversion: operations involving mixed-type operands, the numeric type of the smaller range is converted to the numeric type of the larger range
In an assignment operation, a numeric type of smaller range can be assigned to a numeric type of larger range
Appendix A: Introduction to Java

24. Control Statements: Simple Choice Statement
if (<boolean expression>)
<block>;
else
if (<boolean expression>)
single statement;
else

25. Boolean expression
Boolean expression: is a conditional expression that is evaluated to either true or false.
Conditional expression: is a three part expression:
<exp.> <relational operators> <exp.>
Boolean expressions can be combined by boolean operators

26. Relational Operators

27. && means AND || means OR ! means NOT
Boolean operators
&& means AND || means OR ! means NOT

28. Pre-review question
How many times the method readData() will be called in the following code segnment?
int i; i = 0;
while ( i <= 4 ) {
readData();
i = i + 1;
} // end while 5
Appendix A: Introduction to Java

29. Pre-review question
.          can be used to traverse a two- dimensional array.
a. A do while statement.
b. A for statement.
c. Two nested for statements.
d. Three nested for statements.
Appendix A: Introduction to Java

30. Pre-review question
.          can be used to traverse a two- dimensional array.
a. A do while statement.
b. A for statement.
c. Two nested for statements.
d. Three nested for statements.
Appendix A: Introduction to Java

31. The While Loop while(<boolean expression>){
// Repeat multiple statements.
statement 1
statement 2
statement 3
... }

32. The Do-While Loop do { // Repeat multiple statements. statement 1
...
} while(<boolean expression);
Note that the statements in the body of the loop are always executed at least one.
Note the final semicolon, which is required.

33. The For-Loop Outline Commonly used with increment
// Repeat multiple statements.
for(initialization; condition; post-body update){
// Statements to be repeated.
statement 1
statement 2
statement 3
... }
Commonly used with increment
and decrement operators.

34. Increment and Decrement
Used as a shorthand for add-one-to and subtract-one-from:
value = value+1;
value += 1;
value++;
Prefix and postfix forms:
++value;
--value;
value--;

35. Attributes (Data Member) Declaration
<modifiers> <data type> <name> ;
Modifiers
Data Type
Name
private String ownerName ;
Note: There’s only one modifier in this example.

36. Method Declaration
<modifier> <return type> <method name> ( <parameters> ){
<statements> }
Modifier
Return Type
Method Name
Parameter
public void setOwnerName ( String name ) {
ownerName = name; }
Statements

37. Constructor
A constructor is a special method that is executed when a new instance of the class is created.
public <class name> ( <parameters> ){ <statements> }
Modifier
Class Name
Parameter
public Bicycle ( ) {
ownerName = “Unassigned”; }
Statements

38. Arguments and Parameters
An argument is a value we pass to a method.
A parameter is a placeholder in the called method to hold the value of the passed argument.
class Sample {
public static void
main(String[] arg) {
Account acct = new Account();
. . .
acct.add(400); }
class Account {
. . .
public void add(double amt) {
balance = balance + amt; }
argument

39. Arguments and Parameters
An argument is a value we pass to a method.
A parameter is a placeholder in the called method to hold the value of the passed argument.
class Sample {
public static void
main(String[] arg) {
Account acct = new Account();
. . .
acct.add(400); }
class Account {
. . .
public void add(double amt) {
balance = balance + amt; }
parameter

40. Referencing and Creating Objects
You can declare reference variables that reference objects of specified types
Two reference variables can reference the same object
The new operator creates an instance of a class
A constructor executes when a new object is created
Appendix A: Introduction to Java

41. Methods
Programmers use methods to define a group of statements that perform a particular operation
The modifier static indicates a static or class method
A method that is not static is an instance method
All method arguments are call-by-value
If the argument is a primitive type, its value is passed to the method
The method can’t modify the argument value and have the modification remain after return from the method
Appendix A: Introduction to Java

42. Methods (continued)
If the argument is of a class type, the value of the reference variable is passed, not the value of the object itself
Reference variables point to the object and any modification to the object will remain after return from the method
Appendix A: Introduction to Java

43. Review question Consider the following Java statements: int x = 9;
double y = 5.3;
result = calculateValue( x, y );
Which of the following statements is false?
a. A method is called with its name and arguments inside parentheses.
b. x and y are parameters.
c. Copies of x and y are passed to the method calculateValue().
d. x and y are arguments
Appendix A: Introduction to Java

44. Review question Consider the following Java statements: int x = 9;
double y = 5.3;
result = calculateValue( x, y );
Which of the following statements is false?
a. A method is called with its name and arguments inside parentheses.
b. x and y are parameters.
c. Copies of x and y are passed to the method calculateValue().
d. x and y are arguments
Appendix A: Introduction to Java

45. The Class Math
Provides a collection of methods that are useful for performing common mathematical operations
Appendix A: Introduction to Java

46. Escape Sequences
An escape sequence is a sequence of two characters beginning with the character \
Represents characters or symbols that have a special meaning in Java
Appendix A: Introduction to Java

47. The String Class
String class defines a data type that is used to store a sequence of characters
You cannot modify a String object
If you attempt to do so, Java will create a new object that contains the modified character sequence
Appendix A: Introduction to Java

48. Comparing Objects
You can’t use the relational operators or equality operators to compare the values stored in strings or other objects
Appendix A: Introduction to Java

49. Examples We can do this because String objects are immutable.
By making String objects immutable, we can treat it much like a primitive data type for efficient processing. If we use the new operator to create a String object, a separate object is created as the top diagram illustrates. If we use a simple assignment as in the bottom diagram, then all literal constants refer to the same object. We can do this because String objects are immutable.

50. The StringBuffer Class
Stores character sequences
Unlike a String object, the contents of a StringBuffer object can be changed

51. Pre-review question 7 Consider the Java segment:
String line1 = new String( "c = " ) ;
StringTokenizer tok = new StringTokenizer( line1 );
int count = tok.countTokens();
What is the value of count ? 7
Appendix A: Introduction to Java

52. Pre-review question Consider the Java segment:
String line1 = new String( "c = " ) ;
StringTokenizer tok = new StringTokenizer( line1, delimArg );
For the String line1 to have 4 tokens, delimArg should be:
a. String delimArg = "+=";
b. String delimArg = "123"
c. String delimArg = "c+";
d. String delimArg = " ";

53. Pre-review question Consider the Java segment:
String line1 = new String( "c = " ) ;
StringTokenizer tok = new StringTokenizer( line1, delimArg );
For the String line1 to have 4 tokens, delimArg should be:
a. String delimArg = "+=";
b. String delimArg = "123"
c. String delimArg = "c+";
d. String delimArg = " ";

54. StringTokenizer Class
We often need to process individual pieces, or tokens, in a string
Appendix A: Introduction to Java

55. Wrapper Classes for Primitive Types
Sometimes we need to process primitive-type data as objects
Java provides a set of classes called wrapper classes whose objects contain primitive-type values: Float, Double, Integer, Boolean, Character, etc.
Appendix A: Introduction to Java

56. Defining Your Own Classes
Unified Modeling Language is often used to represent a class
Standard means of documenting class relationships widely used in industry
Appendix A: Introduction to Java

57. Defining Your Own Classes (continued)
The modifier private sets the visibility of each variable or constant to private visibility
These data fields can be accessed only within the class definition
Only class members with public visibility can be accessed outside of the class
Constructors initialize the data fields within a class
Appendix A: Introduction to Java

58. Arrays In Java, an array is also an object
The elements are indexes and are referenced using a subscripted variable of the form arrayname[subscript]
Appendix A: Introduction to Java

59. Review question
A programmer must do the following before using an array: a. declare then reference the array. b. create then declare the array. c. create then reference the array. d. declare then create the array.
Appendix A: Introduction to Java

60. Review question
A programmer must do the following before using an array:
a. declare then reference the array.
b. create then declare the array.
c. create then reference the array.
d. declare then create the array.
Appendix A: Introduction to Java

61. Input/Output using Class JOptionPane (continued)
Appendix A: Introduction to Java

62. Converting Numeric Strings to Numbers
A dialog window always returns a reference to a string
Therefore, a conversion is required
Appendix A: Introduction to Java

63. Input/Output using Streams
An input stream is a sequence of characters representing program data
An output stream is a sequence of characters representing program output
The console keyboard stream is System.in or Scanner
The console window is associated with System.out.print(ln) or Formatter
Appendix A: Introduction to Java