Advice on Methods: Useful Items

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Advice on Methods Useful Items

• Using static classes

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So whats a static class?

• Its a class that doesnt have to be instantiated
  to be used
• Like System.exit(0)
• Like Math.pow( a, b )

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1. Math.round(x)

• double x 47.67
• Int y 0
• y Math.round( x ) returns an int, rounded to
  48
• Use (int) x to truncate (casting)

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2. String.valueOf( any number )

• creates a String when you need it

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3. Integer.parseInt( any String )

• creates an int from a String

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4. Double.parseDouble( any String )

• creates a double from a String

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5. x.substring( start, end )

• String x Have a nice summer
• x.substring(7, 10) yields nice
• Start at 0.
• x.substring( 12 ) yields summer from 12 to
  end
• Also useful
• x.equalsIgnoreCase( anotherString )
• returns a boolean true if the same

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6. Math.random( )

• Returns a double value with a positive sign,
  greater than or equal to 0.0 and less than 1.0.

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7. some other Math methods

• Math.pow (double a, double b)           Returns
  the value of the first argument raised to the
  power of the second argument.
• Math.sqrt( double a )           Returns the
  positive square root of a double value.
• Math.max( a, b ) and Math.min( a, b )

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8. JOptionPane

• Here are three useful static methods from
  javax.swing.JOptionPane that allow you to easily
  create dialog boxes for input and output. The
  Java API documentation has many more JOptionPane
  options, but these are sufficient for many uses.
  In the code below userInput and text are Strings,
  button is an int.
• String userInput  JOptionPane.showInputDialog(
  text )
• JOptionPane.showMessageDialog( component, text )
• int button JOptionPane.showConfirmDialog(
  component, text )
• Use null for the component parameter if you don't
  have a window
• The dialog box will be centered over the
  component given in the first parameter. Typically
  you would give the window over which it should be
  centered. If your program doesn't have a window,
  you may simply write null, in which case the
  dialog box will be centered on the screen.

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9. Shortcuts

• x is the same as x x 1
• String userInput Hello
• userInput how are you? yields
• Hello how are you?
• System.out.println(\nHello)
• when printed, \n skips a line
• System.out.print(Hello)
• does not go to next line

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10. A website

• http//leepoint.net/notes-java/
• I have no idea where this is from.

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11. What if you need a date?

• import java.util.Date
• public class testpublic static void
  main(String args )
  System.out.println("Starting test program")
  Date myDate new Date() System.out.println(
  myDate )

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Use JFrame methods

• import javax.swing.JFrame
• public class JFrameDemo
• public static void main (String args )
• JFrame myWindow new JFrame("Title")
• myWindow.setDefaultCloseOperation(
  myWindow.EXIT_ON_CLOSE )
• myWindow.setLocation( 50, 200 )
• myWindow.setSize( 400, 400)
• myWindow.setVisible(true)

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Using pop-up windows
X0, Y0
X800, Y0
X0, Y600
X800, Y600
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try / catch

• try
• (x Integer.parseInt( stringToConvert ))
• catch (Exception myError)
• System.out.println(Bad Format)
• System.exit(0)

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Methods in the Exception Java Native Class

• try
• x Integer.parseInt(stringToConvert)
• catch(Exception e)
• System.out.println( e.getMessage() ) // what
  user typed
• System.out.println( e.toString()) // error
  message
• e.printStackTrace( ) // where the program
  failed
• System.exit(0)