CIS 3020 Part 3

Syntactic Elements

class SpecialTurtle extends Turtle {
  public void drawTriangle( double sideLength ) {
    final double DEGREES_IN_CIRCLE = 360.0;
    double turnAngle = DEGREES_IN_CIRCLE / 3;
    this.tailDown();
    this.move(sideLength);
    this.turnLeft(turnAngle);
    this.move(sideLength);
    this.turnLeft(turnAngle);
    this.move(sideLength);
    return;
  } // end drawTriangle
} // end class SpecialTurtle

• Keywords (a.k.a. Reserved Words):
  • Examples: class, public, static, void, new, extends, double, this, return, const
  • Have a predefined meaning
  • Can only be used in specific locations within your program
• class - used to define a class
• public - allows everone to access
• static - belonds to the class as a whole, not to an instance of the class
• void - a "return value" of nothing
• new - instantiate an instance (object) of a class
• extends - define a specialized version of a class
• double - defines a type - real number
• this - refers to the current object
• return - stop processing and return the specifed value, if one is given:
  • return;
  • return( expr );
• final - used to define a constant:
  • final double DEGREES_IN_CIRCL 360.0;

Identifiers

• Programmer selected symbolic names for data, operations, and classes
• Contain letters, numbers, underscore
• Start with letter or underscore
• Class names: Demo, Island, Turtle
  • Start with capital letter (stylistic convention)
  • Each subsequent word also is capitalized
• Method names: main, drawTriangle
  • start with lower case letter
  • Each subsequent word is capitalized
• Data names
  • Constants - DEGREES_IN_CIRCLE
    • values that cannot change
    • All upper-case characters with underscores between words
  • Variables - sideLength, turnAngle, tina
    • Start with lower case
    • Each subsequent word is capitalized

Operators

• Predefined by the language
  • [] - array index operator
  • = - gets (the value of), assignment operator
  • . - dot operator - send the message on the right to the object on the left. Not the same as decimal point in number.
  • + - addition operator
  • - - subtraction operator
  • * - multiplication operator
  • / - division operator
  •  % - modulus operator - remainder from division