Practice Problems: Creating Classes and Objects

Try these problems, don’t just look at the answers. If you do look at the answers and find you made mistakes, write the answers out again by hand, even if you are mostly copying the answers. People learn differently from writing versus reading details: you are much more likely to absorb the pattern of defining classes if you actually write it down yourself. If you type instead of write by hand, don’t use cut and paste. You actually have to write out the characters yourself to help you absorb the patterns.

1 The Problems

• Create a class that captures students. Each student has a first name, last name, class year, and major. Create two examples of students.

• Create a class that captures planets. Each planet has a name, a distance from the sun, and its gravity relative to Earth’s gravity. For distance and gravity, use the type double which captures real numbers. Make objects for Earth and your favorite non-earth planet.

• Create classes that capture bank customers and bank accounts. A customer has a first and last name. An account has a customer and a balance. Make objects for two accounts held by the same customer.

• Create a class that captures airline tickets. Each ticket lists the departure and arrival cities, a flight number, and a seat assignment. A seat assignment has both a row and a letter for the seat within the row (such as 12F). Make two examples of tickets.

2 Answers

Here is a link to classes for these questions. You might have used different names for the fields, but your answers should have been close to this. The Examples class is not complete, but just shows you one example of creating data in which one object contains another. Your Examples class should be much more extensive.

2.1 Things to Consider About the Answers

• For seat assignments, you could use a string or you could make a seat-assignment class. What are the advantages and disadvantages of each approach?

• Is there any difference between two customers with the same data and two customers with different data?