- learn to use existing classes
- later, learn to define own
- Java API
  - application programming interface
  - documentation for the standard classes
- null
  - reserved word
  - means no object
- \n: newline character
- method composition: use result of one method as arg for another
- JOptionPane for output
  - display computed result to user
  - window types
    - in graphical user interface (GUI) env
      - general purpose frame, e.g. JFrame
      - special purpose dialog
        - e.g., JDialog
        - method showMessageDialog
          - first argument
            - controlling frame object
            - dialog positioned at center of this, or, if no arg, of screen
          - creates instance of JDialog internally
          - class method
            - don't need to create object to use it
            - just use <class name>.<class method>
- String
  - textual values
  - sequence of chars surrounded by double quotes
  - explicit use of new optional
  - methods
    - substring
      - first argument
        - beginning position
        - note that position numbers count from 0
        - is displayed
      - second argument
        - end position
        - is not displayed
      - creates new string
      - original string left intact
      - generates error if given illogical arguments
    - length: return # chars in str obj
    - indexOf
      - locate index position of substring within another string
      - returns position of first char of substring
      - returns -1 if substring not found
      - case-sensitive
      - returns first occurrence if multiple exist
    - concatenation
      - create a new string from two existing ones
      - <first string> + <second string>
      - cannot concatenate null
    - many others
- Date
  - time instance
  - millisecond (ms) precision
  - in java.util package
  - automatically set to time created
    - obtained from OS
  - toString method converts to human-readable
  - internally represented as elapsed time since epoch
    - epoch: Jan 1, 1970 00:00:00 GMT
    - GMT: Greenwich mean time
  - use GregorianCalendar for real dates
- SimpleDateFormat
  - change display format of Date
  - java.text package
  - pass formatting string when create instance of SimpleDateFormat
  - formatting string case-sensitive
  - common letters for formatting string p. 68
- JOptionPane for input
  - showInputDialog method
  - access input by assigning return result to variable
  - returns null if cancel clicked
  - returns empty string if nothing entered & OK clicked

Quick Check:
1. JOptionPane.showMessageDialog(null, "I Love Java");
2. JOptionPane.showMessageDialog(null, "Shoppint List:\n\tApple\n\tBanana\n\tLowfat Milk");

1. ocha
2. 0
3. 8
4. abcab

1. SimpleDateFormat sdf;
   sdf = new SimpleDateFormat("MM-dd-yyyy");
   JOptionPane.showMessageDialog(null, sdf.format(new Date());
2. Today is Jul 04, 1776

1. initial = JOptionPane.showInputDialog(null, "What is your middle initial?");
2. dorm = JOptionPane.showInputDialog(null, "What's the name of your dorm?");