Method definitions

• Here are four examples of method definitions (declarations), the first two from the Critter class, the third and fourth from the Cell class.
  public void step() {
      turn(1);
      age++;
      paint();
  }
  
  public void turn(int angle) {
      heading = Cell.addDirections(heading, angle);
  }
  public boolean contains(int x, int y) {
      return hex.contains(x, y);
  }
  public static int addDirections(int dir1, int dir2) {
      return (dir1 + dir2) % 6;
  }
• A method definition (declaration) includes the following.
  • A header, for example
    public void turn(int angle)
public boolean contains(int x, int y)
    The header includes
    • Modifiers, such as public, protected, and static. For now the only one that will matter is static; this says that the method is a static method rather than an instance method (the default).
    • The return type for the method, that is, the type of whatever the method returns. If it returns nothing, the keyword void appears. The contains method returns something of type boolean, that is, either true or false.
    • A signature for the method, including
      • The method's name, or identifier
      • A list, between parentheses, of the method's parameters, the variables that must be passed to the method when it is called.
        • Each parameter has a type and an identifier, and the parameters are separated by commas. For example, the two parameters of the contains method are both ints.
        • The parentheses must be there, even if the method has no parameters.
  • A body, made up of zero or more statements, each of them something to be executed in sequence by the method when it is called.
    • The body is surrounded by curly brackets "{}", and each statement is followed by a semicolon ";". For example, here is the body of the turn method:
      {
          heading = Cell.addDirections(heading, angle);
      }
      And here is the body of the step method:
      {
          turn(1);
          age++;
          paint();
      }
    • A method that returns something must contain a return statement. This consists of the keyword return followed by an expression that specifies the value to be returned. See the contains and addDirections methods above.

© 2004. Indiana University and Michael Gasser. www.indiana.edu/~gasser/Q530/Notes/method-defs.html 13 Sep 2004