Java Building Elements Lecture 2

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Java Building ElementsLecture 2

• Instructors
• Fu-Chiung Cheng
• (???)
• Associate Professor
• Computer Science Engineering
• Tatung University
• email cheng_at_cse.ttu.edu.tw
• http// www.cse.ttu.edu.tw/cheng

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Contents

• Introducing Programming with an Example
• Identifiers
• Variables
• Constants
• Primitive Data Types
• Operators
• Expressions
• Programming Errors
• Style and Documentation
• The MyInput class

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Introducing Programming with an Example

• Example 2.1 Computing the Area of a Circle
• This program reads the radius from the keyboard
  and computes the area of the circle.

ComputeArea
Run
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Identifiers

• Identifiers
• class name, method name, variables, key words.
• An identifier can be made up of letters, digits,
  the underscore character (_), and the dollar sign
• An identifier must start with a letter, an
  underscore, or a dollar sign.
• An identifier cannot contain operators, such as
  , -, and be true, false, or null.
• An identifier cannot be a reserved word. (See
  Appendix A, Java Keywords,).
• An identifier can be of any length.
• Java is case sensitive, (e.g. Total and total)

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Variables

• //Compute the first area
• radius 1.0
• area radiusradius3.14159
• System.out.println("The area is"area" for
  radius "radius)
• //Compute the second area
• radius 2.0
• area radiusradius3.14
• System.out.println("The area is "area" for
  radius "radius)

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Declaring Variables

• int x // declares x to be an
• // integer variable
• double radius // declares radius to
• // be a double variable
• char a // declares a to be a
• // character variable

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Assignment Statements

• x 1 // Assign 1 to x
• radius 1.0 // Assign 1.0 to radius
• a 'A' // Assign 'A' to a

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Declaring and Initializingin One Step

• int x 1
• double d 1.4
• float f 1.4

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Constants

• Format
• static final datatype CONSTANT VALUE
• Example
• static final double PI 3.14159
• static final int SIZE 3

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Numerical Data Types

• byte 8 bits
• short 16 bits (2 bytes)
• int 32 bits (4 bytes)
• long 64 bits (8 bytes)
• float 32 bits (4 bytes)
• double 64 bits (8 bytes)

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Number Literals

• int i 34
• long l 1000000
• float f 100.2f orfloat f 100.2F
• double d 100.2d ordouble d 100.2D

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Shortcut Operators
Operator Example Equivalent i8 i
i8 - f-8.0 f f-8.0 i8 i i8 / i/8 i
i/8 i8 i i8
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Increment andDecrement Operators

• x 1
• y 1 x
• y 1 x
• y 1 x--
• y 1 --x

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Numeric Type Conversion

• Consider the following statements
• byte i 100
• long l i34
• double f i3.1l/2

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Primitive Data Type

• double
• float
• long
• Int
• char
• short
• byte
• boolean

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Type Casting

• float f (float)10.1
• int i (int)f

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Character Data Type

• char letter 'A'
• char letter '\u000A'
• char numChar '4'

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Unicode Format
Character Escape Sequence ASCII Unicode Backspace
\b \u0008 Tab \t \u0009 Linefeed \n \u000a Carriag
e return \r \u000d
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The boolean Data Type

• boolean lightsOn true
• boolean lightsOn false

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Operator Precedence

• Casting
• , --
• , /,
• , -
• lt, lt, gt, gt
• , !
• , , -, , /,

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Programming Errors

• Syntax Errors
• Syntax Error
• Runtime Errors
• devided by zero, exceptions
• Logical Errors
• incorrect results, infinite loop

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Naming Conventions

• Variables and method names
• Use lowercase.
• If the name consists of several words,
  concatenate all in one, use lowercase for the
  first word, and capitalize the first letter of
  each subsequent word in the name.
• For example, the variables radius and area, and
  the method computeArea.

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Naming Conventions, cont.

• Class names
• Capitalize the first letter of each word in the
  name.
• For example, the class name TestComputeArea.
• Constants
• Capitalize all letters in constants.
• For example, the constant PI.

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Computing Mortgage
Example 2.2 Computing Mortgage This program lets
the user enter the interest rate, year, and loan
amount and computes monthly payment and total
payment.
MyInput
ComputeMortgage
Run
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Computing Changes
Example 2.3 Breaking Money Changes This program
lets the user enter the amount in decimal user
enter the amount in decimal representing dollars
and cents and output a report listing the
monetary equivalent in single dollars, quarters,
dimes, nickels, and pennies.
BreakChanges
Run