Java Programming Fourth Edition - Rutgers Universityszhou/351/ch02.pdf · Java Programming, Fourth...
Transcript of Java Programming Fourth Edition - Rutgers Universityszhou/351/ch02.pdf · Java Programming, Fourth...
Java Programming Fourth Edition
Chapter 2 Using Data Within a Program
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Objectives
• Use constants and variables • Learn about the int data type • Display variables • Write arithmetic statements • Use the Boolean data type
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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
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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
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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
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Using Constants and Variables (continued)
• Primitive type – Simple data type
• Reference types – More complex data types
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Java Primitive Data Types
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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
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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
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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
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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
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Limits on Integer Values by Type
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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
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Displaying Variables (continued)
• Use dialog box to display values JOptionPane.showMessageDialog()
• Does not accept single numeric variable • Null String
– Empty String – “”
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NumbersDialog Class
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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
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Integer Arithmetic Operators
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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
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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
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Comparison Operators
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Learning About Floating-point Data Types
• Floating-point number – Contains decimal positions
• Floating-point data types – float – double
• Significant digits – Refers to mathematical accuracy
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Limits on Floating-point Values
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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
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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
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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
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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
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Common Escape Sequences
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Using the JOptionPane Class for GUI Input
• Dialog boxes used to accept user input – Input dialog – Confirm dialog
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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
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The HelloNameDialog Class
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Input Dialog Box of the HelloNameDialog Application
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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
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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()
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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
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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
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Confirm Dialog Box with Title, Yes and No Buttons, and Error Icon
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You Do It
• Working with numeric values • Adding variables to a class • Concatenating strings • Using arithmetic statements • Using boolean variables • Using floating-point variables
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You Do It (continued)
• Using character variables • Using escape sequences • Using variables in dialog boxes • Using a dialog box for input
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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
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Summary (continued)
• Comparison operators – >, <, ==, >=, <=, and !=
• Floating-point data types – float – double
• Unifying type • char data type • JOptionPane
– Confirm dialog – Input dialog