• Used Integers and Plus Operator
  • All five integer operators:
    +, -, *, /, %

    Operator Precedence

• The String Class

  Declaration:

  String message;

  String Constant

  "Good Morning World!"

  String Assignment

  message = "It's Friday";

• String Has Many Methods for Manipulation
  • Most important ones are: length(), indexOf(), substring()
  • Note that character positions start at zero!

• int word.length()
  • Returns the length of the string word as an integer

• int word.indexOf(String st)
  • Returns position of start of first match of st in word
  • Returns -1 if there is no match

• String word.substring(int start, int end)
  • Returns a String that is part of word
  • start is position in word of first char of the substring
  • end is position in word of first char after the substring

• If word contains "Good Afternoon!"
  • word.length() yields 15
  • word.indexOf("tern") yields 7
  • word.indexOf("Tern") yields -1
  • word.substring(5, 8) yields "Aft"

• Getting String Data from the User
  • The TextField class has getText() method.
  • Can use:
    
    message = mg.getText();
    where mg is a TextField and message is a String.

• Example Doing Some String Manipulation
  StringPlay.java, StringPlay.html

• An Algorithm: The Exchange Problem
  • at start:
  • x contains "milk"
  • y contains "juice"
  • how do we interchange contents?
  • need temp

  String x, y, temp;

  ...

  x = ____.getText();

  y = ____.getText();

  _____.setText(x + " and " + y " before");

  ...

  temp = x;

  x = y;

  y = temp;

  ...

  _____.setText(x + " and " + y " after");

  ...

• Add More Functions
  • Last name first format
  • All Capitals ( String toUpperCase())
  • Does last name contain first?

• More About Syntax
  • need a precise notation
  • more formal method
  1. <name> -> //a sequence of letters and/or digits that begin with a letter//
     where // indicates italics in textbook
     read: an object called a 'name' can be ...
  
  could have used:
  1. <name> -> a sequence of letters and/or digits that begin with a letter
     but will use // notation.
     
     Example:
     <name> -> msg42
     <name> -> PigLatin
  
  
  
  
  
  
  
  

• First List

  
   <name> ==> any string of alphanumeric symbols that begins with a letter
   <statement> ==> <name> = <expression>;
   <statement> ==> <name> = new <class>(<arguments>);
   <statement> ==> <name>.<method>(<arguments>); | <method>(<arguments>);
   <arguments> ==>  possibly empty list of <expression>s separated by commas
   <expression> ==> <string-expression> | <int-expression> | <oth-expression>
   <string-expression> ==>  <string-expression> + <string-expression>
   <string-expression> ==>  <string>
   <string> ==> " any sequence of characters "
   <string> ==> <name>
  
  

• To Use: substitute, multiple times as necessary

• Statement Example
  Want: person = firstn + " " + lastn;

 EXAMPLE:
<statement> -> <name> = <expression>;
<statement> -> person = <expression>;
<statement> -> person = <str expression>;
<statement> -> person = <str expression> + <str expression>;
<statement> -> person = <string> + <str expression>;
<statement> -> person = <name> + <str expression>;
<statement> -> person = firstn + <str expression>;
<statement> -> person = firstn + <string> + <str expression>;
<statement> -> person = firstn + " " + <str expression>;
<statement> -> person = firstn + " " + <string>;
<statement> -> person = firstn + " " + <name>;
<statement> -> person = firstn + " " + lastn;