© 2007 Lawrenceville Press Slide 1 Chapter 7 Top-Down Development  Problem-solving approach  Breaking a task down into smaller subtasks  First level of subtasks translates into the main() method  Levels of tasks below main() are developed into a series of additional methods

© 2007 Lawrenceville Press Slide 2 Chapter 7 Using Methods  Used to implement a specific task  Methods must be part of a class  A main() method defines the first level of subtasks with calls to methods that implement the subtasks  Using methods to define tasks is called procedural abstraction

© 2007 Lawrenceville Press Slide 3 Chapter 7 A Method public static void fahrenheitToCelsius() { double fTemp, cTemp; Scanner input = new Scanner(System.in); System.out.println("Enter a Fahrenheit temperature: "); fTemp = input.nextDouble(); input.close; cTemp = (double)5/(double)9 * (fTemp - 32); System.out.println("The Celsius temperature is "+cTemp); } class method access level return type method name body

© 2007 Lawrenceville Press Slide 4 Chapter 7 Method Parameters  A method can have parameters for accepting values from a calling statement  Parameters are used inside the method to perform the method's task  The data passed to a method are called arguments  The drawBar() method declaration has one parameter named length: public static void drawBar(int length)

© 2007 Lawrenceville Press Slide 5 Chapter 7 Pass by Value  In Java, arguments are passed by value  A primitive data type gives the method a copy of its value. The method does not have access to the original data.  An object gives the method a copy of its reference that points to methods for changing object data. A method can change the data stored in an object because the method has access to the object's methods.

© 2007 Lawrenceville Press Slide 6 Chapter 7 Multiple Parameters  A method can have multiple parameters  Multiple parameters must be separated by commas  The order of the arguments passed must match the order of the parameters  The modified drawBar() method declaration has two parameters: public static void drawBar(int length, String mark)

© 2007 Lawrenceville Press Slide 7 Chapter 7 Method Overloading  More than one method of the same name can be included in a class  The compiler uses the types, order, and number of parameters to determine which method to execute

© 2007 Lawrenceville Press Slide 8 Chapter 7 The return Statement  A return statement is used to send a value back to the calling statement  A return statement can return only one value  A method that returns a value must include the return type in the method declaration. For example, the cubeOf() method returns a double : public static double cubeOf(double x)  A method that returns a value is called from a statement that will make use of the returned value. For example: cube = cubeOf(num);

© 2007 Lawrenceville Press Slide 9 Chapter 7 Documenting Methods  Methods should be carefully commented so that a reader of the program understands what task the method is performing and what data, if any, will be returned by the method  Method documentation should appear just above a method  Documentation should include a brief description of the method, any preconditions, and the postcondition

© 2007 Lawrenceville Press Slide 10 Chapter 7 Preconditions and Postconditions  The precondition states what must be true at the beginning of a method for the method to work properly.  The postcondition states what must be true after the method has executed if the method has worked properly.  Preconditions and postconditions should not state facts that the compiler will verify. They should also not refer to variables or information outside the method.  The postcondition should not state how the method accomplished its task.

© 2007 Lawrenceville Press Slide 11 Chapter 7 The GradeConverter Flowchart