1. Chapter 6 The while Statement
11/13/2018 7:10 PM
Chapter 6 The while Statement
Loop structure that executes a set of statements as long as a condition is true
The condition is a Boolean expression
Will never execute if the condition is initially false
The loop below iterates once because the condition is true and then continues to iterate until response is not 1: response = 1; while (response == 1) { System.out.print("Enter 1 or 0:"); response = input.nextInt(); }
Refer to page 131 in the text.
© 2007 Lawrenceville Press

2. Chapter 6 The do-while Statement
11/13/2018 7:10 PM
Chapter 6 The do-while Statement
Alternative form of the while statement
Executes at least once
The statement do { System.out.print("Enter 1 or 0:"); response = input.nextInt(); } while (response == 1); iterates once and continues to iterate until response is not 1.
Refer to pages 131 and 132 in the text.
© 2007 Lawrenceville Press

3. Chapter 6 Infinite Loops
11/13/2018 7:10 PM
Chapter 6 Infinite Loops
A loop that continues executing forever
Can be caused by syntax or logic errors. For example: while (num < 0) //error--no braces System.out.print("Enter a vale: "); num = input.nextInt();
Some errors can result in an overflow
Refer to page 132 in the text.
An infinite loop can cause an application to stop responding or just "hang". Closing the application window (with JCreator Pro) will end the application so that the source of the infinite loop can be located and corrected.
Errors that result in an overflow may generate unexpected results rather than "hanging" the application.
© 2007 Lawrenceville Press

4. A variable that is incremented by a constant value
11/13/2018 7:10 PM
Chapter 6 Counters
A variable that is incremented by a constant value
Often used for counting loop iterations
Should be initialized to 0 when declared
The counter in the loop counts the number of responses: do { System.out.print("Enter 1 or 0:"); response = input.nextInt(); numResponses += 1; } while (response == 1);
Refer to page 133 in the text.
© 2007 Lawrenceville Press

5. A variable that is incremented by a varying amount
11/13/2018 7:10 PM
Chapter 6 Accumulators
A variable that is incremented by a varying amount
Often used for summing
Should be initialized to 0 when declared
The accumulator in the loop sums values: do { System.out.print("Enter grade:"); grade = input.nextInt(); sumOfGrades += grade; } while (grade != 999);
Refer to page 133 in the text.
© 2007 Lawrenceville Press

6. A flag, or sentinel, indicates when a loop should stop iterating
11/13/2018 7:10 PM
Chapter 6 Using Flags
A flag, or sentinel, indicates when a loop should stop iterating
Often a constant
Code is easier to modify when sentinels are constants declared at the beginning of an application
A flag is used in the condition of the loop: final int STOP = 999; do { System.out.print("Enter grade:"); grade = input.nextInt(); sumOfGrades += grade; } while (grade != STOP);
Refer to page 133 in the text.
© 2007 Lawrenceville Press

7. Chapter 6 The for Statement
11/13/2018 7:10 PM
Chapter 6 The for Statement
Loop structure that executes a set of statements a fixed number of times
Uses a loop control variable (lcv)
The increment (++) or decrement (--) operators are used to change the value of the loop control variable
The loop below executes until i is greater than 10: for (int i = 0; i <= 10; i++) { sum += i; }
Refer to page 135 in the text.
© 2007 Lawrenceville Press

8. Chapter 6 Debugging Techniques
11/13/2018 7:10 PM
Chapter 6 Debugging Techniques
The debugger included with many compilers
Variable trace, which is a manual technique of list values of variables at the points of assignment
Additional println() statements for displaying variable values at points of assignment
"Commenting out" code to detect bugs through a process of elimination
Refer to pages 136 and 137 in the text.
© 2007 Lawrenceville Press

9. Chapter 6 Variable Trace
11/13/2018 7:10 PM
Chapter 6 Variable Trace
int num1 = 0; int num2 = 0; while (num1 < 10) { if (num1 % 3 == 0) { num2 += num1; System.out.print(num2 + " "); } num1 += 1; }
Refer to page 136 in the text.
© 2007 Lawrenceville Press

10. Chapter 6 Using println() to Debug
11/13/2018 7:10 PM
Chapter 6 Using println() to Debug
int num1 = 0; int num2 = 0; System.out.println("num1 before while: " + num1); //debug while (num1 < 10) { System.out.println("num1 in while: " + num1); //debug if (num1 % 3 == 0) { num2 += num1; System.out.println("num2: " + num2); //debug System.out.print(num2 + " "); } num1 += 1; }
Refer to page 137 in the text.
When using println() statements to debug a segment of code, it is usually most effective to place statements just after assignment changes the value of a variable.
© 2007 Lawrenceville Press

11. Chapter 6 Using Comments to Debug
11/13/2018 7:10 PM
Chapter 6 Using Comments to Debug
int num1 = 0; int num2 = 0; while (num1 < 10) { //if (num1 % 3 == 0) { // num2 += num1; // System.out.print(num2 + " "); //} num1 += 1; }
Refer to page 137 in the text.
Comments can be used to comment out segments of code to determine through a process of elimination the location of any bugs.
© 2007 Lawrenceville Press

12. Chapter 6 The String Class
11/13/2018 7:10 PM
Chapter 6 The String Class
Part of the java.lang package
A String object is comprised of a sequence of characters with the first character at index position 0
String methods include: length() isEmpty() substring() toLowerCase() toUpperCase() trim() replaceFirst() replaceAll()
Refer to page 138 in the text.
The String class is used for representing text. The first character of a string is at index position 0. The last character is at position length()-1.
© 2007 Lawrenceville Press

13. Chapter 6 String Data and the Scanner Class
11/13/2018 7:10 PM
Chapter 6 String Data and the Scanner Class
The next() method should be used for reading string data after numeric data has been read. If the nextLine() method is used, the end-of-line character left by the numeric entry is read and any text typed is ignored.
System.out.print("Enter age: "); age = input.nextInt(); System.out.print("Enter first name: "); firstName = input.next();
Refer to page 138 in the text. You may also want to refer students back to page 82.
The nextInt() and nextDouble() methods read in data up to an end-of-line character. The nextLine() method reads data up to and including the end-of-line character. Because of this, calling a nextLine() method after a nextInt() or nextDouble() reads the end-of-line left by those methods and the string entry just made is lost.
© 2007 Lawrenceville Press

14. Chapter 6 String Data and the Scanner Class (con't)
11/13/2018 7:10 PM
Chapter 6 String Data and the Scanner Class (con't)
Alternatively, a statement can be added to read the end-of-line character left by the numeric entry, so that the nextLine() method can be used to read a string that may contain white space:
System.out.print("Enter age: "); age = input.nextInt(); input.nextLine(); //remove end-of-line System.out.print("Enter full name: "); fullName = input.nextLine();
Refer to page 138 in the text. You may also want to refer students back to page 82.
Note that an input.nextLine() statement can be added to simply remove the end-of-line left by the numeric entry.
© 2007 Lawrenceville Press

15. Chapter 6 String Assignment
11/13/2018 7:10 PM
Chapter 6 String Assignment
Strings are immutable. Assigning a new string to a String object simply changes the object reference to point to the new string in memory:
String text;
text = "heLlO";
text = text.toLowerCase();
text
heLlO
hello
Note: This slide contains animations. Press the space bar or click the mouse button to display each animation.
This slide contains three (3) animations.
Refer to page 139 in the text.
The object instantiation, String text, associates the object name text with a memory location <press space bar>
The first assignment statement points to the location in memory that stores the mixed-case string <press space bar>
The second assignment statement, moves the pointer to the location in memory that stores the lowercase string <press space bar>
© 2007 Lawrenceville Press

16. Chapter 6 Comparing Strings
11/13/2018 7:10 PM
Chapter 6 Comparing Strings
The String class includes several methods for comparing two strings: equals() equalsIgnoreCase() compareTo() compareToIgnoreCase() indexOf() lastIndexOf() startsWith() endsWith()
Refer to page 140 in the text.
© 2007 Lawrenceville Press