Principles of Programming using Java

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Principles of Programming using Java
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Control of Flow

• SEQUENCE
• SELECTION
• REPETITION

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Selection Statements

• ifelse
• switchcase

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Repetition - iteration

• used to repeat one or more programming statements
• Data Input
• e.g. for inputting a number of items of data
• - inputting a class of students marks
• Processing
• e.g for doing a series of calculations
• - adding up the total of each students marks
  scored
• Output
• e.g. for outputting a number of items of data
• - outputting each of the student totals

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while loops

• while loops continue to loop while some condition
  is true, and stops when the condition becomes
  false
• while (condition) do this
• while (age lt 18)
• System.out.println(You cant drink)
• age

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Repetition - deterministic loop

• public class Drinker
• public static void main(String args)
• int age0
• while(age lt18)
• System.out.println(You are too young
  to drink")
• age age1
• System.out.println(You can now
  drink")

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Non- deterministic loops- sentinel controlled
loops
Enter a data item
Does this value match the sentinel?
YES
NO
process the item
enter a data item
exit the loop
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non-deterministic loop sentinel controlled

• import javax.swing.JOptionPane
• public class Sentinel
• public static void main(String args)
• int input1
• while(input !0 )
• String s1 JOptionPane.showInputDialog("Enter
  your choice, 0 to end")
• input Integer.parseInt(s1)
• if(input1)
• System.out.println("chocolate
  selected")
• else
• if(input2)
• System.out.println("fruitgums selected")
• else
• System.out.println("Nothing
  selected")

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Counter controlled repetition

• for loop is a deterministic loop
• i.e. it executes a fixed number of times, which
  is known before the execution of the loop
• for(counter starting value condition changes to
  counter)
• statement(s)

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Iteration for loops

• for loops allow us to repeat a statement or group
  of statements, a fixed number of times
• for (starting value condition counter)
• for (num 0 num lt 10 num)
• System.out.println(Count from 0 to num )

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• public class Forloop
• public static void main(String args)
• int sum0
• for(int count 1 countlt10 count)
• sum sum count
• System.out.println(Sum of the integers 1 to 10
  sum)

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• write a program using the for loop, to convert
  yards 1 to 10, to inches.
• DISPLAY Yards Inches
• FOR count 1 TO 10
• inches count 36
• DISPLAY count inches

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• write a program using the for loop that will take
  a number from the user and produce an
• n times table for the first 6 numbers
• GET num
• FOR count 1 TO 6
• sum num count
• DISPLAY count num sum

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do while loop

• In do while loops the test condition comes at the
  end of the loop. So, the loop always iterates at
  least once.
• do
• statement(s)
• while(condition)

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do while loop

• int num JOptionPane.showInputDialog(Enter
  number)
• do
• if(num1)
• System.out.println(chocolate selected)
• else
• if(num2)
• System.out.println(sherbet selected)
• else
• System.out.println(peanuts default choice)
• while(num gt 0)

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Which Loop, When?

• for loop when you know how many times the loop
  will be executed
• while loop when you dont know how many times
  the loop will execute, including when the user is
  in control
• while loop when you may not want the loop to
  execute even once
• do while when you want the loop to execute even
  once

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JTextArea
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JTextArea

• JTextArea outputArea new JTextArea()
• String output This is what I want in my
  TextArea - row 1\n and this on row 2
• outputArea.setText(output)
• JOptionPane.showMessageDialog(null, outputArea,
  "Results", JOptionPane.INFORMATION_MESSAGE)

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DecimalFormat

• import java.text.
• public class Format
• public static void main(String args)
• double result0 int first 4, second3
• result (double) first/second
• System.out.println(result)
• DecimalFormat twoplaces new DecimalFormat("0.00"
  )
• String output twoplaces.format(result)
• System.out.println(output)
• System.out.println(twoplaces.format(result))

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