1. Iteration

2. Java looping Options while do-while for
Allow programs to control how many times a statement list is executed

3. Averaging
Problem
Extract a list of positive numbers from standard input and produce their average
Numbers are one per line
A negative number acts as a sentinel to indicate that there are no more numbers to process
Observations
Cannot supply sufficient code using just assignments and conditional constructs to solve the problem
Don’t how big of a list to process
Need ability to repeat code as needed

4. Averaging
Problem
Extract a list of positive numbers from standard input and produce their average
Numbers are one per line
A negative number acts as a sentinel to indicate that there are no more numbers to process
Algorithm
Prepare for processing
Get first input
While there is an input to process do {
Process current input
Get the next input }
Perform final processing
NumberAverage.java

5. While syntax and semantics
When a while statement is executed, its test expression is evaluated first. If the expression evaluates true, its body is executed, where the body is the action of the while statement. The evaluation process then is repeated. If the expression reevaluates to true, the body is executed again. This process is called looping, and it continues until the test expression evaluates to false. At that point, execution continues with the next statement in the program.

6. While semantics for averaging problem
When a while statement is executed, its test expression is evaluated first. If the expression evaluates true, its body is executed, where the body is the action of the while statement. The evaluation process then is repeated. If the expression reevaluates to true, the body is executed again. This process is called looping, and it continues until the test expression evaluates to false. At that point, execution continues with the next statement in the program.

7. Averaging
Problem
Extract a list of positive numbers from standard input and produce their average
Numbers are one per line
A negative number acts as a sentinel to indicate that there are no more numbers to process
Sample run
Enter positive numbers one per line.
Indicate end of list with a negative number.
4.5
0.5
1.3 -1
Average 2.1

8. While Semantics

9. Execution Trace Suppose input contains: 4.5 0.5 -1
int valuesProcessed = 0;
double valueSum = 0;
double value = stdin.nextDouble());
while (value >= 0) {
valueSum += value;
++valuesProcessed;
value = stdin.nextDouble()); }
if (valuesProcessed > 0) {
double average = valueSum / valuesProcessed;
System.out.println("Average: " + average);
else {
System.out.println("No list to average");
The tracing of the execution of a method by hand is an important program debugging technique. Hand-checking code can give insight into how a method works.
Service.java

10. Execution Trace Suppose input contains: 4.5 0.5 -1 valuesProcessed
int valuesProcessed = 0;
double valueSum = 0;
double value = stdin.nextDouble());
while (value >= 0) {
valueSum += value;
++valuesProcessed;
value = stdin.nextDouble()); }
if (valuesProcessed > 0) {
double average = valueSum / valuesProcessed;
System.out.println("Average: " + average);
else {
System.out.println("No list to average");
The tracing of the execution of a method by hand is an important program debugging technique. Hand-checking code can give insight into how a method works.

11. Execution Trace Suppose input contains: 4.5 0.5 -1 valuesProcessed
int valuesProcessed = 0;
double valueSum = 0;
double value = stdin.nextDouble());
while (value >= 0) {
valueSum += value;
++valuesProcessed;
value = stdin.nextDouble()); }
if (valuesProcessed > 0) {
double average = valueSum / valuesProcessed;
System.out.println("Average: " + average);
else {
System.out.println("No list to average");
valueSum

12. Execution Trace Suppose input contains: 4.5 0.5 -1 valuesProcessed
int valuesProcessed = 0;
double valueSum = 0;
double value = stdin.nextDouble());
while (value >= 0) {
valueSum += value;
++valuesProcessed;
value = stdin.nextDouble()); }
if (valuesProcessed > 0) {
double average = valueSum / valuesProcessed;
System.out.println("Average: " + average);
else {
System.out.println("No list to average");
valueSum
value
4.5

13. Execution Trace Suppose input contains: 4.5 0.5 -1 valuesProcessed
int valuesProcessed = 0;
double valueSum = 0;
double value = stdin.nextDouble());
while (value >= 0) {
valueSum += value;
++valuesProcessed;
value = stdin.nextDouble()); }
if (valuesProcessed > 0) {
double average = valueSum / valuesProcessed;
System.out.println("Average: " + average);
else {
System.out.println("No list to average");
valueSum
value
4.5

14. Execution Trace Suppose input contains: 4.5 0.5 -1 valuesProcessed
int valuesProcessed = 0;
double valueSum = 0;
double value = stdin.nextDouble());
while (value >= 0) {
valueSum += value;
++valuesProcessed;
value = stdin.nextDouble()); }
if (valuesProcessed > 0) {
double average = valueSum / valuesProcessed;
System.out.println("Average: " + average);
else {
System.out.println("No list to average");
valueSum
4.5
value
4.5

15. Execution Trace Suppose input contains: 4.5 0.5 -1 valuesProcessed 1
int valuesProcessed = 0;
double valueSum = 0;
double value = stdin.nextDouble());
while (value >= 0) {
valueSum += value;
++valuesProcessed;
value = stdin.nextDouble()); }
if (valuesProcessed > 0) {
double average = valueSum / valuesProcessed;
System.out.println("Average: " + average);
else {
System.out.println("No list to average");
valueSum
4.5
value
4.5

16. Execution Trace Suppose input contains: 4.5 0.5 -1 valuesProcessed 1
int valuesProcessed = 0;
double valueSum = 0;
double value = stdin.nextDouble());
while (value >= 0) {
valueSum += value;
++valuesProcessed;
value = stdin.nextDouble()); }
if (valuesProcessed > 0) {
double average = valueSum / valuesProcessed;
System.out.println("Average: " + average);
else {
System.out.println("No list to average");
valueSum
4.5
value
0.5
4.5

17. Execution Trace Suppose input contains: 4.5 0.5 -1 valuesProcessed 1
int valuesProcessed = 0;
double valueSum = 0;
double value = stdin.nextDouble());
while (value >= 0) {
valueSum += value;
++valuesProcessed;
value = stdin.nextDouble()); }
if (valuesProcessed > 0) {
double average = valueSum / valuesProcessed;
System.out.println("Average: " + average);
else {
System.out.println("No list to average");
valueSum
4.5
value
0.5

18. Execution Trace Suppose input contains: 4.5 0.5 -1 valuesProcessed 1
int valuesProcessed = 0;
double valueSum = 0;
double value = stdin.nextDouble());
while (value >= 0) {
valueSum += value;
++valuesProcessed;
value = stdin.nextDouble()); }
if (valuesProcessed > 0) {
double average = valueSum / valuesProcessed;
System.out.println("Average: " + average);
else {
System.out.println("No list to average");
valueSum
4.5
5.0
value
0.5

19. Execution Trace Suppose input contains: 4.5 0.5 -1 valuesProcessed 2 1
int valuesProcessed = 0;
double valueSum = 0;
double value = stdin.nextDouble());
while (value >= 0) {
valueSum += value;
++valuesProcessed;
value = stdin.nextDouble()); }
if (valuesProcessed > 0) {
double average = valueSum / valuesProcessed;
System.out.println("Average: " + average);
else {
System.out.println("No list to average");
valueSum
5.0
value
0.5

20. Execution Trace Suppose input contains: 4.5 0.5 -1 valuesProcessed 2
int valuesProcessed = 0;
double valueSum = 0;
double value = stdin.nextDouble());
while (value >= 0) {
valueSum += value;
++valuesProcessed;
value = stdin.nextDouble()); }
if (valuesProcessed > 0) {
double average = valueSum / valuesProcessed;
System.out.println("Average: " + average);
else {
System.out.println("No list to average");
valueSum
5.0
value -1
1.3

21. Execution Trace Suppose input contains: 4.5 0.5 -1 valuesProcessed 2
int valuesProcessed = 0;
double valueSum = 0;
double value = stdin.nextDouble());
while (value >= 0) {
valueSum += value;
++valuesProcessed;
value = stdin.nextDouble()); }
if (valuesProcessed > 0) {
double average = valueSum / valuesProcessed;
System.out.println("Average: " + average);
else {
System.out.println("No list to average");
valueSum
5.0
value -1

22. Execution Trace Suppose input contains: 4.5 0.5 -1 valuesProcessed 2
int valuesProcessed = 0;
double valueSum = 0;
double value = stdin.nextDouble());
while (value >= 0) {
valueSum += value;
++valuesProcessed;
value = stdin.nextDouble()); }
if (valuesProcessed > 0) {
double average = valueSum / valuesProcessed;
System.out.println("Average: " + average);
else {
System.out.println("No list to average");
valueSum
5.0
value -1

23. Execution Trace Suppose input contains: 4.5 0.5 -1 valuesProcessed 2
int valuesProcessed = 0;
double valueSum = 0;
double value = stdin.nextDouble());
while (value >= 0) {
valueSum += value;
++valuesProcessed;
value = stdin.nextDouble()); }
if (valuesProcessed > 0) {
double average = valueSum / valuesProcessed;
System.out.println("Average: " + average);
else {
System.out.println("No list to average");
valueSum
5.0
value -1
average
2.5

24. Execution Trace Suppose input contains: 4.5 0.5 1.3 -1 valuesProcessed2
int valuesProcessed = 0;
double valueSum = 0;
double value = stdin.nextDouble());
while (value >= 0) {
valueSum += value;
++valuesProcessed;
value = stdin.nextDouble()); }
if (valuesProcessed > 0) {
double average = valueSum / valuesProcessed;
System.out.println("Average: " + average);
else {
System.out.println("No list to average");
valueSum
5.0
value -1
average
2.5

25. Loop design Questions to consider in loop design and analysis
What initialization is necessary for the loop’s test expression?
What initialization is necessary for the loop’s processing?
What causes the loop to terminate?
What actions should the loop perform?
What actions are necessary to prepare for the next iteration of the loop?
What conditions are true and what conditions are false when the loop is terminated?
When the loop completes what actions are need to prepare for subsequent program processing?

26. Sentinel
For some input data sets there is no reasonable sentinel value
Examples
Process a series of arbitrary numbers
Processing lines of arbitrary text
What can we do?
Use Scanner methods and an operating system sentinel
hasNext()
hasNextInt()
...
We will only use hasNext()
MSDOS sentinel Unix sentinel MAC sentinel
CTRL-Z CTRL-D ?

27. Reading a file
Background

28. Reading a file Class File
Provides a system-independent way of representing a file name
Constructor File(String s)
Creates a File with name s
Name can be either an absolute pathname or a pathname relative to the current working folder

29. Echoing a file Scanner stdin = new Scanner(System.in);
System.out.print("Filename: ");
String filename = stdin.next();
File file = new File(filename);
Scanner fileIn = new Scanner(file);
while (fileIn.hasNext()) {
String currentLine = fileIn.nextLine();
System.out.println(currentLine); }
fileIn.close();

30. Reading a file Scanner stdin = new Scanner(System.in);
System.out.print("Filename: ");
String filename = stdin.next();
File file = new File(filename);
Scanner fileIn = new Scanner(file);
while (fileIn.hasNext()) {
String currentLine = fileIn.nextLine();
System.out.println(currentLine); }
fileIn.close();
Set up standard input stream

31. Reading a file Scanner stdin = new Scanner(System.in);
System.out.print("Filename: ");
String filename = stdin.next();
File file = new File(filename);
Scanner fileIn = new Scanner(file);
while (fileIn.hasNext()) {
String currentLine = fileIn.nextLine();
System.out.println(currentLine); }
fileIn.close();
Determine file name

32. Reading a file Scanner stdin = new Scanner(System.in);
System.out.print("Filename: ");
String filename = stdin.next();
File file = new File(filename);
Scanner fileIn = new Scanner(file);
while (fileIn.hasNext()) {
String currentLine = fileIn.nextLine();
System.out.println(currentLine); }
fileIn.close();
Determine the associated file

33. Reading a file Scanner stdin = new Scanner(System.in);
System.out.print("Filename: ");
String filename = stdin.next();
File file = new File(filename);
Scanner fileIn = new Scanner(file);
while (fileIn.hasNext()) {
String currentLine = fileIn.nextLine();
System.out.println(currentLine); }
fileIn.close();
Set up file stream

34. Reading a file Scanner stdin = new Scanner(System.in);
System.out.print("Filename: ");
String filename = stdin.next();
File file = new File(filename);
Scanner fileIn = new Scanner(file);
while (fileIn.hasNext()) {
String currentLine = fileIn.nextLine();
System.out.println(currentLine); }
fileIn.close();
Process lines one by one

35. Reading a file Scanner stdin = new Scanner(System.in);
System.out.print("Filename: ");
String filename = stdin.next();
File file = new File(filename);
Scanner fileIn = new Scanner(file);
while (fileIn.hasNext()) {
String currentLine = fileIn.nextLine();
System.out.println(currentLine); }
fileIn.close();
Is there any text

36. Reading a file Scanner stdin = new Scanner(System.in);
System.out.print("Filename: ");
String filename = stdin.next();
File file = new File(filename);
Scanner fileIn = new Scanner(file);
while (fileIn.hasNext()) {
String currentLine = fileIn.nextLine();
System.out.println(currentLine); }
fileIn.close();
Get the next line of text

37. Reading a file Scanner stdin = new Scanner(System.in);
System.out.print("Filename: ");
String filename = stdin.next();
File file = new File(filename);
Scanner fileIn = new Scanner(file);
while (fileIn.hasNext()) {
String currentLine = fileIn.nextLine();
System.out.println(currentLine); }
fileIn.close();
Display current line

38. Reading a file Scanner stdin = new Scanner(System.in);
System.out.print("Filename: ");
String filename = stdin.next();
File file = new File(filename);
Scanner fileIn = new Scanner(file);
while (fileIn.hasNext()) {
String currentLine = fileIn.nextLine();
System.out.println(currentLine); }
fileIn.close();
Make sure there is another to process
If not, loop is done

39. Reading a file Scanner stdin = new Scanner(System.in);
System.out.print("Filename: ");
String filename = stdin.next();
File file = new File(filename);
Scanner fileIn = new Scanner(file);
while (fileIn.hasNext()) {
String currentLine = fileIn.nextLine();
System.out.println(currentLine); }
fileIn.close();
Close the stream

40. The For Statement

41. The For Statement

42. The For Statement

43. The For Statement

44. The For Statement

46. For statement syntax

47. Execution Trace for (int i = 0; i < 3; ++i) {
System.out.println("i is " + i); }
System.out.println("all done"); i

48. Execution Trace for (int i = 0; i < 3; ++i) {
System.out.println("i is " + i); }
System.out.println("all done"); i

49. Execution Trace for (int i = 0; i < 3; ++i) {
System.out.println("i is " + i); }
System.out.println("all done");
i is 0 i

50. Execution Trace for (int i = 0; i < 3; ++i) {
System.out.println(“i is " + i); }
System.out.println(“all done");
i is 0 i

51. Execution Trace for (int i = 0; i < 3; ++i) {
System.out.println("i is " + i); }
System.out.println("all done");
i is 0 i 1

52. Execution Trace for (int i = 0; i < 3; ++i) {
System.out.println("i is " + i); }
System.out.println("all done");
i is 0 i 1

53. Execution Trace for (int i = 0; i < 3; ++i) {
System.out.println("i is " + i); }
System.out.println("all done");
i is 0
i is 1 i 1

54. Execution Trace for (int i = 0; i < 3; ++i) {
System.out.println("i is " + i); }
System.out.println("all done");
i is 0
i is 1 i 1

55. Execution Trace for (int i = 0; i < 3; ++i) {
System.out.println("i is " + i); }
System.out.println("all done");
i is 0
i is 1 i 2

56. Execution Trace for (int i = 0; i < 3; ++i) {
System.out.println("i is " + i); }
System.out.println("all done");
i is 0
i is 1 i 2

57. Execution Trace for (int i = 0; i < 3; ++i) {
System.out.println("i is " + i); }
System.out.println("all done");
i is 0
i is 1
i is 2 i 2

58. Execution Trace for (int i = 0; i < 3; ++i) {
System.out.println("i is " + i); }
System.out.println("all done");
i is 0
i is 1
i is 2 i 2

59. Execution Trace for (int i = 0; i < 3; ++i) {
System.out.println("i is " + i); }
System.out.println("all done");
i is 0
i is 1
i is 2 i 3

60. Execution Trace for (int i = 0; i < 3; ++i) {
System.out.println("i is " + i); }
System.out.println("all done");
i is 0
i is 1
i is 2 i 3

61. Variable i has gone out of scope – it
Execution Trace
for (int i = 0; i < 3; ++i) {
System.out.println("i is " + i); }
System.out.println("all done");
i is 0
i is 1
i is 2
all done 3
i is undefined – its scope is limited to the loop
Variable i has gone out of scope – it
is local to the loop

62. Nested loops int m = 2; int n = 3; for (int i = 0; i < n; ++i) {
System.out.println("i is " + i);
for (int j = 0; j < m; ++j) {
System.out.println(" j is " + j); }
is part of the action associated with the for loop that begins on the third line of the segment. We say that this loop is the outer loop. The expression i < n that controls the iteration of the loop evaluates to true three times with i taking on in turn the values 0, 1, and 2. Thus, there are three lines of output that begin with “i is ”. Each time there is such a display, the for loop beginning on the fifth line of the segment is executed. We say this loop is an inner or nested loop.
It is important to realize that an inner loop starts up once per iteration of its outer loop. For our example, each time the inner loop is executed, the expression j < m evaluates to true two times with j taking on in turn the values 0 and 1.
Nesting one loop in another loop produces a multiplicative effect in terms of the number of statements that are executed. For our example, the outer for loop action is executed n times. Each one of those times, the inner for loop action is executed m times. As a result, the inner for loop action is performed a total of m  n times.

63. What’s the output Counting.java int counter1 = 0; int counter2 = 0;
for (int i = 0; i < 5; ++i) {
++counter1;
for (int j = 0; j < 10; ++j) {
++counter2;
for (int k = 0; k < 2; ++k) {
++counter3; }
++counter4;
++counter5;
System.out.println(counter1 + " " + counter2 + " " + counter3
+ " " + counter4 + " " + counter5);

64. What’s the output
Implement a program that displays the first n numbers in the Fibonacci sequence, where n is a user-specified integer value
The sequence starts with the following numbers: 1, 1, 2, 3, 5, 8, 13, 21
After the initial two 1s, each number in the sequence is the sum of the two previous numbers. For example, = 2, = 3, = 5, = 8, and so on
Fibonacci.java

65. The do-while statement
Syntax
do Action
while (Expression)
Semantics
Execute Action
If Expression is true then execute Action again
Repeat this process until Expression evaluates to false
Action is either a single statement or a group of statements within braces
Action
true
Expression
false

66. Picking off digits Consider
System.out.print("Enter a positive number: ");
int number = stdin.nextInt());
do {
int digit = number % 10;
System.out.println(digit);
number = number / 10;
} while (number != 0);
Sample behavior
Enter a positive number: 1129 9 2 1
There is always at least one digit to display. A segment with a while loop would be either awkward or have repeated code

67. Problem solving

68. Internet per 100 people for 189 entities

69. Data set manipulation Often five values of particular interest Minimum
Maximum
Mean
Standard deviation
Size of data set
Let’s design a data set representation
Together the minimum and maximum let us know the range of the values; the mean is the average data set value, which often gives insight on what is a typical value; and the standard deviation gives insight on how clustered the data set values are around the average. (Our implementation of a data set representation DataSet.java leaves the computing of a standard deviation to the exercises.)

70. What facilitators are needed?

71. Implication on facilitators
public double getMinimum()
Returns the minimum value in the data set. If the data set is empty, then Double.NaN is returned, where Double.NaN is the Java double value representing the status not-a-number
public double getMaximum()
Returns the maximum value in the data set. If the data set is empty, then Double.NaN is returned

72. Implication on facilitators
public double getAverage()
Returns the average value in the data set. If the data set is empty, then Double.NaN is returned
public double getStandardDeviation()
Returns the standard deviation value of the data set. If the data set is empty, then Double.NaN is returned
Left to the interested student
public int getSize()
Returns the number of values in the data set being represented

73. What constructors are needed?

74. Constructors public DataSet()
Initializes a representation of an empty data set
public DataSet(String s)
Initializes the data set using the values from the file with name s
public DataSet(File file)
Initializes the data set using the values from the file
Left to interested student

75. Other methods public void addValue(double x)
Adds the value x to the data set being represented
public void clear()
Sets the representation to that of an empty data set
public void load(String s)
Adds the vales from the file with name s to the data set being represented
public void load(File file)
Adds the vales from the file to the data set being represented
Left to interested student

76. What instance variables are needed?

77. Instance variables private int n
Number of values in the data set being represented
private double minimumValue
Minimum value in the data set being represented
private double maximumValue
Maximum value in the data set being represented
private double xSum
The sum of values in the data set being represented

78. Example usage DataSet dataset = new DataSet("age.txt");
System.out.println();
System.out.println("Minimum: " + dataset.getMinimum());
System.out.println("Maximum: " + dataset.getMaximum());
System.out.println("Mean: " + dataset.getAverage());
System.out.println("Size: " + dataset.getSize());
dataset.clear();
dataset.load("stature.txt");

79. Example usage dataset.load("foot-length.txt");
System.out.println("Minimum: " + dataset.getMinimum());
System.out.println("Maximum: " + dataset.getMaximum());
System.out.println("Mean: " + dataset.getAverage());
System.out.println("Size: " + dataset.getSize());
System.out.println();
dataset.clear();

80. Example usage

81. Methods getMinimum() and getMaximum()
Straightforward implementations given correct setting of instance variables
public double getMinimum() {
return minimumValue; }
public double getMaximum() {
return maximumValue;

82. Method getSize()
Straightforward implementations given correct setting of instance variables
public int getSize() {
return n; }

83. Method getAverage()
Need to take into account that data set might be empty
public double getAverage() {
if (n == 0) {
return Double.NaN; }
else {
return xSum / n;

84. DataSet constructors Straightforward using clear() and load()
public DataSet() {
clear(); }
public DataSet(String s) throws IOException {
load(s);

85. Facilitator clear() public void clear() { n = 0; xSum = 0;
minimumValue = Double.NaN;
maximumValue = Double.NaN; }

86. Facilitator add() public void addValue(double x) { xSum += x; ++n;
if (n == 1) {
minimumValue = maximumValue = x; }
else if (x < minimumValue) {
minimumValue = x;
else if (x > maximumValue) {
maximumValue = x;

87. Facilitator load() public void load(String s) throws IOException {
// get a reader for the file
Scanner fileIn = Scanner.create( new File(s) );
// add values one by one
while (fileIn.hasNext()) {
double x = fileIn.nextDouble);
addValue(x); }
// close up file
fileIn.close();