Lecture Summary for 211 on 3/26/04 -- Barat Section

Review Questions

1. Explain the difference between an accessor method and a mutator method.

2. Match the method types in Column 1 with the items in Column 2.
   

   Column 1	Column 2
   Mutator	One return value
   Accessor	No return value
   	One parameter
   	No parameter

3. Which type of method does not specify a return type in its header.

4. What is wrong with this constructor definition?
   public MyClass()
   {
       MyClass x = MyClass();
   }

5. What is garbage? How do you create it and get rid of it?

6. What gets printed?
   Kid x = new Kid("Mary", 'F', 12);
   Kid y = new Kid("Tom", 'M', 10);
   Kid temp;

   temp = x;
   x = y;
   y = temp;

   System.out.println(x);
   System.out.println(y);

7. Write lines of Java code that print "yes" if x is female and "no" otherwise. Assume the class definition Kids2. Do not hardcode your answer for this particular x.

8. Write lines of Java code that print the length of the name for y. Do not hardcode your answer for this particular y.

9. Write an equals method for the Point class. Two Point objects p and q are equal if p.x == q.x and q.x == q.y.

10. Write a main method to test your equals method in the previous problem.

The StringTokenizer

• A token is a string with a meaning for an application.

• Use a StringTokenizer object to extract tokens from a string.

• Example 1: the string "345,34,21,5,2341" contains the tokens 345, 34, 21, 5, and 2341. Since the tokens are separated by commas, the string is called a "comma delimited string."

• Example 2: the string "Jane F 13" contains the tokens Jane, F, and 13. The original string is a space delimited string.

• Look at the StringTokenizer Example in Debugging (Debugging.zip or Debugging.txt).

Arrays in Java

• Look at the Arrays in Java document.

• Look at the Arrays Example in Arrays.

• Look at the Trace 5 Example.

The Sorting Examples

• Look at the KidArray and IntSorting Examples in Arrays.

• Look at the Phone Example in Arrays.
  This application looks up a name entered in an array and prints the associated phone number.

The Art of Debugging

• Debugging is often more of an art than it is a science.

• Avoid the temptation to experiment on a buggy program before understanding the bugs.

• The best weapon for finding bugs is thinking.

The Steps of Inductive Debugging

1. Collect data about the bug. When does the program perform correctly and when does it perform incorrectly.

2. Organize the data. Answer these questions: what, when, and where. When does an error occur and when does it not occur?

3. Formulate a hypotheses about what is causing the bug.

4. Prove the hypotheses.

5. Fix the bug and continue to look for more bugs. Resist the urge to skip directly from Step 3 to Step 5.

The BlueJ Debugger

• Invoke the debugger by selecting the main menu item View, then checking the box Show Debugger.

• Set breakpoints in the code window by clicking with the mouse in the left border of the code window. The code will pause in its execution when it reaches a breakpoint.

• Continue to step through the code by clicking the Step button at the bottom of the debugger. Step continues to the next line of the code. Step Into steps into the code of a method if one is invoked on the next line.

• Values of all variables, including instance variables and local variables, are shown.

• Some people do not like to use debuggers. The effect of a debugger can be simulated by placing strategic print or println statements in the code.

Debugging Examples

• Debug the WagesForMonth and MaxSalary Examples in Debugging (Debugging.zip or Debugging.txt).

• Here are the errors in the examples and the main method to test the English method in MetricConverter.