Outline
Creating Objects
The String Class
Packages
Formatting Output
Enumerated Types
Wrapper Classes
Components and Containers
Images
Formatting output

It is often necessary to format values


output looks appropriate when printed or displayed
NumberFormat part of java.text package

Provides generic formatting capabilities

is not instantiated using the new operator

instead by requesting an object

From one of the static methods invoked thru the class name
 NumberFormat fmt =
NumberFormat.getCurrencyInstance();
Creating NumberFormat
instance

NumberFormat objects

are created using

getCurrencyInstance() invoked thru class name


getPercentInstance() invoked thru class name


returns a formatter for monetary values
returns an object that formats a percentage
are used to format numbers using method format()
NumberFormat fmt =
NumberFormat.getCurrencyInstance()
double subtotal=19.35;
System.out.println(fmt.format(subtotal) );
Output: $19.35

Refer to Purchase.java
DecimalFormat class

DecimalFormat part of java.text package

allows to format values based on a pattern


To determine how many digits should be printed
 To the right of the decimal point (for instance)
is instantiated in the traditional way

using the new operator

Its constructor DecimalFormat takes a String


That represents a pattern for the formatted number
Refer to CircleStats.java
Outline
Creating Objects
The String Class
Packages
Formatting Output
Enumerated Types
Wrapper Classes
Components and Containers
Images
Enumerated types

Java allows you to define an enumerated type

Which can then be used to declare variables


as the type of a variable
establishes all possible values for a variable of that type

By listing, or enumerating the values

Where the values are identifiers, and can be anything desired
 enum Season {winter, spring, summer, fall}

There is no limit to the number of listed values
 Any number of values can be listed
Declaring and using an
enumerated type

Once a type is defined

A variable of that type can be declared


And it can be assigned a value


enum Grade {A, B, C, D, F};
Grade score;
Thru the name of the type
score = Grade.A;
Enumerated types are type-safe

You cannot assign any value other than those listed
Ordinal values

Internally, each value of an enumerated type

is stored as an integer, called its ordinal value

The first value has an ordinal value of zero


The second one, and so on
You cannot assign a numeric value

to enumerated type, even if it corresponds to an ordinal value
Enumerated types: methods

The declaration of an enumerated type

is a special type of class


methods associated with enumerated objects

The ordinal() method returns the numeric value



And each variable of that type is an object
Of an enumerated type
The name() returns the name of the value
Refer to IceCream.java
Outline
Creating Objects
The String Class
Packages
Formatting Output
Enumerated Types
Wrapper Classes
Components and Containers
Images
Wrapper classes

A wrapper class

is used to wrap a primitive value into an object


represents a particular primitive type


Ex: Integer class represents a simple integer value
instantiated, stores a single primitive type value


Ex: create an object that serves as a container to hold an int
Ex: Integer object store a single int value
its constructor accept the primitive value to store

Ex: Integer ageObj = new Integer (40);
Wrapper classes in the JAVA
class library

For each primitive type in JAVA

There exists a corresponding wrapper class (java.lang)
Primitive type
Wrapper class
byte
Byte
short
Short
int
Integer
long
Long
float
Float
double
Double
char
Character
boolean
Boolean
Wrapper classes methods

Wrapper classes methods

manages the associated primitive type


Ex: Integer provides methods returning the int stored in it
Some methods of the Integer class

Integer (int value)


float floatValue()


Constructor: creates an new Integer object storing value
returns the value of this integer as the float type
static int parseInt (String str)

Returns the int corresponding to the value in str
Autoboxing/Unboxing

Autoboxing is the automatic conversion between
 Primitive value and corresponding wrapper object


Unboxing is the reverse condition


Integer obj1;
int num1 = 69;
Obj1 = num1; // automatically creates an Integer object
Integer obj2 = new Integer (69);
int num2;
num2 = Obj2; // automatically extracts the int value
Refer to wrapper_error.java
Using Dialog Boxes for
Input/Output

Another way to gather input is to use a GUI

such as JOptionPane offered by Java



Which allows a programmer to use GUI for I/O
Making I/O more efficient and the program more attractive
JOptionPane


Contained in the package javax.swing
Offers two methods:


ShowInputDialog: allows user to input a string from keyboard
ShowMessageDialog: allows user to display results
Syntax for ShowInputDialog

To display a dialog box



Containing the string in the object stringExpression
Storing the input data in the String object str
The syntax to use the method is:


str = JOptionPane.showInputDialog(stringExpression);
A dialog appears on the screen



prompting user to enter data
Data is returned as a string and assigned to variable str
The user enters the data in the white area

Called text field
Syntax for
showMessageDialog

The syntax to use showMessageDialog is

JoptionPane.showMessageDialog(null,
messageStringExpression, boxTitleString,
messageType).



messageStringExpression:evaluated and value appears in box
boxTitleString: the title of the dialog box
messageType: type of icon appearing in the dialog box
 JoptionPane.ERROR_MESSAGE
 JoptionPane.INFORMATION_MESSAGE
 JoptionPane.Question_MESSAGE
 JoptionPane.PLAIN_MESSAGE
 JoptionPane.WARNING_MESSAGE