• Read and trace existing programs.
• Use and enhance existing class definitions.
• Design a class definition from a specification.
  • What data does the object keep track of? (fields)
  • What should the object look like when it is created? (constructor)
  • How can code outside access object information? (accessor methods)
  • How can code outside modify object information? (modifier methods)
  • What other actions should an object be able to take? (other methods)
• Design an entire program from a specification.

The frog problem:

In this class period we will focus on developing a program from a specification. The program we are going to develop models random walks, an important idea in statistics and in many scientific fields. (The random frog was originally proposed by Owen Astrachan in Computer Science Tapestry. See Other Links on the class web page for more information on random walks.)

A frog lives on a lily pad in LiliWorld, a straight line of lily pads stretching in two directions. The frog's home position (lily pad) is represented by 0. The frog moves in LiliWorld by tossing a coin. Heads indicates a step to the right (add one to current position) and tails indicates a step to the left (subtract one from current position). This (most intelligent) frog also keeps track of how many steps it has taken and its current position. (See class demo.)

• Design a basic frog program and test and run it.
• Enhance the program to gather the following statistics.
  • How often the frog visits the home lily pad.
  • How far from the home lily pad the frog is at the end of the walk.
  • The furthest points from home reached by the frog in both positive and negative.

A few methods from the predefined Math class are useful here.

• random() returns a pseudorandom number between 0.0 and 1.0. It takes a double argument and returns a double.
• abs(x) returns the absolute value of x (x is any numeric type.)

The Frog class and test program as developed in class can be found at here