Programming Principles using Java

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Programming Principles using Java
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Program Structure

• Many programs have this structure

Data Input
Processing
Output results
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Retirement Program

• PROMPT Enter your age
• GET age
• STORE age
• years 65 age
• OUTPUT You will retire in years years

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Program Structure
Data Input //prompt String myAge
JOptionPane.showInputDialog(Enter your
age) //assign to variable int age
Integer.parseInt(myAge)
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Data Input - prompt
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Program Structure

• Processing
• \\work out how many years to retirement
• int years 65 - age

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Program Structure

• Output
• \\display how many years to retirement
• JOptionPane.showMessageDialog(
• null,
• You will retire in years years,
• Output, JOptionPane.PLAIN_MESSAGE)

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Output
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Retirement program

• import javax.swing.JOptionPane
• public class Retirement
• public static void main(String args)
• \\prompt
• String myAge JOptionPane.showInputDialog(Enter
  your age)
• \\convert to an int and assign to a variable
• int age Integer.parseInt(myAge)
• \\processing
• int years 65 - age
• \\output results of processing
• JOptionPane.showMessageDialog(null, You will
  retire in years years, Output,
  JOptionPane.PLAIN_MESSAGE)
• System.exit(0)

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Program flow

• Control of flow is the order in which program
  statements are executed
• There are 3 types
• SEQUENCE
• SELECTION
• REPETITION

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SELECTION

• Sometimes the code you execute depends upon
  whether a condition is true
• if(pin 1234)
• Then you can access your bank account
• if(passwordp1w234)
• Then you can access your university account

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Selection Statements

• Selection statements allow the program to choose
  between alternate actions during execution
• if (ltconditional expressiongt)
• ltstatementgt
• if (age gt 18)
• System.out.println(You can buy a drink)

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if else Statement

• if (conditional expression)
• ltstatement1gt
• else
• ltstatement2gt
• if (age gt 18)
• System.out.println(You can buy a drink)
• else
• System.out.println(Sorry, wait until you are
  18)

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Using Blocks

• To include more than one statement to be executed
  if a condition is true, put them in a block, i.e.
  
• if(age gt 18)
• System.out.println(You can buy a drink)
• System.out.println(You can go to University)

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Relational Operators

• Relational Operator Test Condition
• a b equal to
• ! a ! b not equal to
• lt a lt b less than
• lt a lt b less than or equal to
• gt a gt b greater than
• gt a gt b greater than or equal to

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Selection Program

• PROMPT Enter your pin number
• GET input
• STORE input
• IF pin input
• OUTPUT You can access your account
• ELSE
• OUTPUT You CANNOT access your account

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Selection Program

• import javax.swing.JOptionPane
• public class Access
• public static void main(String args)
• int pin 1234
• String myInput
• int input
• myInput JOptionPane.showInputDialog(Enter your
  pin number)
• input Integer.parseInt(myInput)
• if(pininput)
• JOptionPane.showMessageDialog(null, You CAN
  access your account, Results,
  JOptionPane.PLAIN_MESSAGE)
• else
• JOptionPane.showMessageDialog(null, You CANNOT
  access the account, Results,
  JOptionPane.PLAIN_MESSAGE)
• System.exit(0)

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Drinking Program

• PROMPT Enter your age
• GET age
• STORE age
• IF age gt 18
• OUTPUT You can drink
• ELSE
• OUTPUT Sorry, wait until you are 18

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Selection Program

• import javax.swing.JOptionPane
• public class Drinking
• public static void main(String args)
• int drinkAge 18
• String myInput
• int input
• myInput JOptionPane.showInputDialog(Enter your
  age )
• input Integer.parseInt(myInput)
• if(input gt drinkAge)
• JOptionPane.showMessageDialog(null, You can buy
  a drink, Results, JOptionPane.PLAIN_MESSAGE)
• else
• JOptionPane.showMessageDialog(null, Sorry wait
  until you are 18, Results, JOptionPane.PLAIN_ME
  SSAGE)
• System.exit(0)

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Boolean Logical Operators

• (AND) (OR) (XOR) !( NOT)
• The operands of boolean operators are boolean
  expressions.
• Their evaluation results in a boolean expression

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Truth Table for Boolean Operators

• P Q !P P Q P Q P Q
• true true false true true false
• true false false false true true
• false true true false true true
• false false true false false false

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Examples

• if((age gt5) (age lt16))
• System.out.print(You are of school age)
• if((age lt 5) (age gt 16))
• System.out.print(You are not of school age)
• if((x gt 10) (x lt 12))
• System.out.print(Your number is in range)

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Conditional Operators ,

• Conditional operators are like boolean logical
  operators, except that their evaluation is
  short-circuited.
• The left operator is evaluated before the right
  one.
• x y true if both operands are true
• x y true if either or both operands are
  true

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