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IC211
Lecture 8
I/O: Command Line
And
JOptionPane
Outline
• Review Project 1 Specification
• A Review of Scope
• Command Line Input
– Wrapper Classes (Integer, Double, etc)
• I/O with JOptionPane
Scope
• Same as C++
• Variable exists only within the block where
it was declared
• Duplicate variable names within the same
class file
• Example: execution class from Lab 4
• Example: scope worksheet
Command Line Input
• Core Java 2 pg 84
• public static void main (String[] args)
• args contains arguments from the
command line
• Ex: MakeShape –c 3.5
args[0]: -c
args[1]: 3.5
Both are Strings!
Converting Strings to Numbers
(Wrapper Classes)
• Used to convert primitive types to Objects.
• Wrapper classes (Core Java pg 186)
– Double, Float, Integer, Long, Short, Byte, Character,
Boolean
• Some containers only hold objects, not primitives
• Can also be used to convert Strings to numbers
• Need to convert String representation 3.5 to
numeric 3.5
– Double.parseDouble(String s)
– Java SE 6 API
• Ex: MakeShape.java
Comparing Integers, Doubles, etc.
for Equality
Scanner in = new Scanner(System.in);
System.out.println("Enter two integers: ");
Integer a = new Integer(in.nextInt());
Integer b = new Integer(in.nextInt());
if (a == b)
System.out.println("Same!");
else
System.out.println("Different!");
Enter two integers: 100 100
Output> ???
Different!
Must use .equals() method vice ==, just like
we do with Strings
JOptionPane
• Create message or dialog boxes without overhead
of full GUI application
• Get input from the user with an input dialog box
String name = JOptionPane.showInputDialog("What's your name?");
• Part of the javax.swing package
JOptionPane
• Getting numeric input…must still use and
input dialog box
String input = JOptionPane.showInputDialog("Guess a number
from 0 to 100");
Convert String input to numeric using wrapper classes
int number = Integer.parseInt(input);
JOptionPane
• Display a message with a message dialog
box
JOptionPane.showMessageDialog(null, "Welcome to IC211!");
JOptionPane
• Getting a confirmation (yes/no) with a
confirmation dialog box
int done = JOptionPane.showConfirmDialog(null, “Are you finished?”);
Returns an int equal to one of three static constants:
– JOptionPane.YES_OPTION
– JOptionPane.NO_OPTION
– JOptionPane.CANCEL_OPTION
JOptionPane Example
(Number Game)
• Guess a number from 0 to 100
– Version using console input (Scanner)
– JOptionPane version