• Parameter values
• Using methods to control access

Methods

• Here is a sample method for the Body class. The method name is toString.

    public String toString()
    {
        String desc = idNum + " (" + name + ")";
        if orbits != null)
        {
            desc += " orbits " + orbits.toString();
        }
        return desc;
    }
  

• Returns type String.
• Methods contain the code that understands and manipulates an object's state.
• Methods are invoked as operations on an object using the . (dot) operator.
• Each method takes a specific number of parameters.
• Each parameter has a specified type - primitive or object.
• Methods also have a return type (or void).

Parameter values

• All parameter methods are "pass by value".
• Values of a parameter are copies of the values in the invoking method.
• When the parameter is an object, the object reference is passed by value.
• End result: primitives cannot be modified in methods, objects can.

Using methods to control access

• If data fields (attributes) are public, programmers can change them.
• Generally want to hide the data from programmers that will use the class.
• If programmers can access a class's fields directly, you have no control over what values they can assign.
• In the Body example, nextIDshould be private.
• If necessary, you should provide get methods that allow programmers to determine the current field value, and set methods to modify the value. These are called accessors (get) and mutators (set).