Java Programming Fourth Edition

Chapter 2 Using Data Within a Program

Java Programming, Fourth Edition 2

Objectives

•  Use constants and variables •  Learn about the int data type •  Display variables •  Write arithmetic statements •  Use the Boolean data type

Java Programming, Fourth Edition 3

Objectives (continued)

•  Learn about floating-point data types •  Understand numeric type conversion •  Work with the char data type •  Use the JOptionPane class for GUI input

Java Programming, Fourth Edition 4

Using Constants and Variables

•  Constant –  Cannot be changed while program running

•  Variable –  Might change while programming running

•  Literal constant –  Value taken literally at each use

Java Programming, Fourth Edition 5

Using Constants and Variables (continued)

•  Variable –  Named memory location –  Use to store value –  Can hold only one value at a time –  Value can change

•  Data type –  Type of data that can be stored –  How much memory item occupies –  What types of operations can be performed on data

Java Programming, Fourth Edition 6

Using Constants and Variables (continued)

•  Primitive type –  Simple data type

•  Reference types –  More complex data types

Java Programming, Fourth Edition 7

Java Primitive Data Types

Java Programming, Fourth Edition 8

Declaring Variables

•  Name variables –  Using naming rules for legal class identifiers

•  Variable declaration –  Statement that reserves named memory location –  Includes

•  Data type •  Identifier •  Optional assignment operator and assigned value •  Ending semicolon

Java Programming, Fourth Edition 9

Declaring Variables (continued)

•  Assignment operator –  Equal sign (=) –  Value to right assigned to variable on left

•  Initialization –  Assignment made when declaring variable

•  Assignment –  Assignment made after variable declared

•  Associativity –  Order in which operands used with operators

Java Programming, Fourth Edition 10

Declaring Variables (continued)

•  Declare multiple variables of same type in separate statements on different lines int myAge = 25;

int yourAge = 19;

•  Declare variables of different types –  Must use separate statement for each type

Java Programming, Fourth Edition 11

Learning About the int Data Type

•  Type int –  Store (or hold) integers, or whole numbers –  Value from –2,147,483,648 to +2,147,483,647

•  Variations of the integer type –  byte –  short –  long

•  Choose appropriate types for variables

Java Programming, Fourth Edition 12

Limits on Integer Values by Type

Java Programming, Fourth Edition 13

Displaying Variables

•  print() or println() statement –  Alone or in combination with string

•  Concatenated –  Numeric variable concatenated to String using plus

sign –  Entire expression becomes String

•  println() method can accept number or String

Java Programming, Fourth Edition 14

Displaying Variables (continued)

•  Use dialog box to display values JOptionPane.showMessageDialog()

•  Does not accept single numeric variable •  Null String

–  Empty String –  “”

Java Programming, Fourth Edition 15

NumbersDialog Class

Java Programming, Fourth Edition 16

Writing Arithmetic Statements

•  Arithmetic operators –  Perform calculations with values in programs

•  Operand –  Value used on either side of operator

•  Integer division –  Integer constants or integer variables –  Result is integer –  Fractional part of result lost

Java Programming, Fourth Edition 17

Integer Arithmetic Operators

Java Programming, Fourth Edition 18

Writing Arithmetic Statements (continued)

•  Operator precedence –  Rules for order in which parts of mathematical

expression evaluated –  First multiplication, division, and modulus –  Then addition or subtraction

Java Programming, Fourth Edition 19

Using the Boolean Data Type

•  Boolean logic –  Based on true-or-false comparisons

•  Boolean variable –  Can hold only one of two values –  True or false

boolean isItPayday = false;

•  Comparison operator –  Compares two items

Java Programming, Fourth Edition 20

Comparison Operators

Java Programming, Fourth Edition 21

Learning About Floating-point Data Types

•  Floating-point number –  Contains decimal positions

•  Floating-point data types –  float –  double

•  Significant digits –  Refers to mathematical accuracy

Java Programming, Fourth Edition 22

Limits on Floating-point Values

Java Programming, Fourth Edition 23

Understanding Numeric Type Conversion

•  Arithmetic with variables or constants of same type –  Result of arithmetic retains same type

•  Arithmetic operations with operands of unlike types –  Java chooses unifying type for result

•  Unifying type –  Type to which all operands in expression converted

for compatibility

Java Programming, Fourth Edition 24

Understanding Numeric Type Conversion (continued)

•  Order for establishing unifying types between two variables –  1. double –  2. float –  3. long –  4. int

•  Type casting –  Forces value of one data type to be used as value of

another type

Java Programming, Fourth Edition 25

Working with the char Data Type

•  char data type –  Holds any single character

•  Place constant character values within single quotation marks

char myMiddleInitial = 'M';

•  String –  Built-in class –  Store and manipulate character strings –  String constants written between double quotation

marks

Java Programming, Fourth Edition 26

Working with the char Data Type (continued)

•  Escape sequence –  Begins with backslash followed by character –  Represents single nonprinting character char aNewLine = '\n';

•  Produce console output on multiple lines in command window –  Use newline escape sequence –  Use println() method multiple times

Java Programming, Fourth Edition 27

Common Escape Sequences

Java Programming, Fourth Edition 28

Using the JOptionPane Class for GUI Input

•  Dialog boxes used to accept user input –  Input dialog –  Confirm dialog

Java Programming, Fourth Edition 29

Using Input Dialog Boxes

•  Input dialog box –  Asks question –  Provides text field in which user can enter response

•  showInputDialog() method –  Six overloaded versions –  Returns String representing user’s response

•  Prompt –  Message requesting user input

Java Programming, Fourth Edition 30

The HelloNameDialog Class

Java Programming, Fourth Edition 31

Input Dialog Box of the HelloNameDialog Application

Java Programming, Fourth Edition 32

Using Input Dialog Boxes (continued)

•  showInputDialog() –  Version requires four arguments

•  Parent component •  Message •  Title •  Type of dialog box

•  Convert String to int or double –  Use methods from built-in Java classes Integer

and Double

Java Programming, Fourth Edition 33

Using Input Dialog Boxes (continued)

•  Type-wrapper classes –  Each primitive type has corresponding class

contained in java.lang package –  Include methods to process primitive type values Integer.parseInt()

Double.parseDouble()

Java Programming, Fourth Edition 34

Using Confirm Dialog Boxes

•  Confirm dialog box –  Displays options Yes, No, and Cancel

•  showConfirmDialog() method in JOptionPane class –  Four overloaded versions available –  Returns integer containing either:

JOptionPane.YES_OPTION JOptionPane.NO_OPTION

JOptionPane.CANCEL_OPTION

Java Programming, Fourth Edition 35

Using Confirm Dialog Boxes (continued)

•  Create confirm dialog box with five arguments –  Parent component –  Prompt message –  Title –  Integer that indicates which option button to show –  Integer that describes kind of dialog box

Java Programming, Fourth Edition 36

Confirm Dialog Box with Title, Yes and No Buttons, and Error Icon

Java Programming, Fourth Edition 37

You Do It

•  Working with numeric values •  Adding variables to a class •  Concatenating strings •  Using arithmetic statements •  Using boolean variables •  Using floating-point variables

Java Programming, Fourth Edition 38

You Do It (continued)

•  Using character variables •  Using escape sequences •  Using variables in dialog boxes •  Using a dialog box for input

Java Programming, Fourth Edition 39

Summary

•  Variables –  Named memory locations

•  Primitive data types –  boolean, byte, char, double, float, int, long, and short

•  Standard arithmetic operators for integers –  +, _, *, /, and %

•  Boolean type –  True or false value

Java Programming, Fourth Edition 40

Summary (continued)

•  Comparison operators –  >, <, ==, >=, <=, and !=

•  Floating-point data types –  float –  double

•  Unifying type •  char data type •  JOptionPane

–  Confirm dialog –  Input dialog