Lecture Summary for 211 on 6/25/03 -- O'Hare

Review Questions

1. Write a line of Java code that converts the String s to the int n.

2. Write a line of Java code that converts the String s to the double x.

3. Write a line of Java code that converts the double x to the int n.

4. List as many methods as you can from these classes:
   
   1. String
      
   2. Applet
      
   3. Graphics
      
5. Write a complete Java main method that inputs two ints in input dialogs and prints their maximum.

6. Input your distance from the city center as the number of blocks East or West from the center and the number of blocks North or South from the center. Compute the distance "as the crow flies" from the city center. Hint: use the Pythagorian Theorem.

7. Identify these parts of this for loop: initialization, condition, iteration.
   for(i = 5; i <= 25; i += 2)
       System.out.println(i * i);

8. What is the major difference between a while loop and a for statement?

9. What is the major difference between a while loop and an if statement?

10. True or False: A while loop must execute at least once.

11. What is a reference variable?

Practice Problems

// Problem 1
i = 0;
while(i <= 100)
{
    System.out.print(i + " ");
    i *= 2;
}

// Problem 2
i = 1;
while(i <= 100)
{
    System.out.print(i + " ");
    i *= 1;
}

// Problem 3
i = 1;
while(i <= 100);
{
    System.out.print(i);
    i *= 1;
}

// Problem 4
// In this loop, start high and end low.
i = 128;
while i < 1
{
    System.out.print(i + " ")
    i /= 2;
}

Sequential Processing

• Sequential processing means reading input data in a while loop and processing it "on the fly" without saving it.

• Most sequential processing of information can be accomplished using the following algorithm (called an input-update loop):

  read first item
  while (not at end of list)
  {
      update summary statistics
      read next item
  }

• Look at the examples Average1 and Average2 in Average (Average.zip and Average.txt).

• Two ways to signal the application that the list is finished:
  • Enter the count of list items before starting to read the list,

  • Use a sentinel, a special value that marks the end of the list. Examples of sentinels: 999, -1, "Quit", "" (empty string), null object generated by Cancel.

• Note: pressing the enter key has the same effect as clicking on OK on the input dialog.

• Note: pressing the escape key (Esc) has the same effect as clicking on Cancel on the input dialog.

  Write a Java application that inputs a list of items in input dialogs. The user clicks on Cancel to terminate the list.
  Here are the answers.

Practice Problems using Sequential Processing

1. Input a list of ints and output the minimum value.

2. Input a list of strings and output the average length of the strings.

3. Input a list of names, gender, and salary. Output the average salary of men and of women.

4. Input a list of ints. Output the largest even int.

5. Input a list of names and salaries. Output the names of the persons with the largest and second largest salary.

The Currency Project

String Processing Problems

1. Count and output the number of vowels.
   Hint: convert the string to upper case first so you only need to check 'A', 'E', 'I', 'O', and 'U'.

2. Count and output the number of upper case letters.
   Hint: A character is upper case if it is greater than or equal to 'A' and less than or equal to 'Z'.

3. Output true if the string contains at least one digit, false otherwise.
   Hint: A character is a digit if it is greater or equal to '0' and less than or equal to '9'.

4. Output true if every character in the string is an asterisk, false otherwise.

5. Output true if the string contains at least one x.

6. Output true if the string begins and ends with the same character. Consider the possibility that the length of the string is zero.

• To count the number of desired characters, initialize a counter to zero and add one to the counter (counter++) each time a desired character is found.

• To check the existence of a desired character, count the number of times the character occurs. If the count equals 0, return false. If the count is greater than 0, return true.

• To check that all characters in a string are equal to a specified character, count the number of times the character occurs. If the count equals the length of the string, return true, otherwise return false.

More Practice Problems

1. Input a string and a letter. Output "Yes" if the string begins with the letter and "No" otherwise.

2. Input a string consisting of digits. Output the sum of the digits.

3. Input an int. Output "Prime" if the int is a prime number. Output "Composite" if the int is not a prime number.

4. Rewrite the main method of the VendingMachine project using a nested for loop.

   Here are the answers.

Work Problems from Practice Midterm Exams

• We worked these problems in class:
  Practice Midterm A: 1, 2.
  Practice Midterm B: 1a.
  Practice Midterm C: 1, 4.
  Practice Midterm D: 1, 5.