1. Java basics – part 3

2. Where are we Last time Constants and variables Initialization
Simple expressions
Casting
Interactive programs
Scanner
This time
Assignment
Operators
Assign programming assignment to compute windchill
Discuss new lab

3. public static void main(String[] args) {
// define constants
final double KILOGRAMS_PER_POUND = 0.454;
final double METERS_PER_FOOT = ;
// set up person's characteristics
double weightInPounds = 75.5; // our person’s weight
double heightInFeet = 4.5; // our person’s height
// convert to metric equivalents
double metricWeight = weightInPounds * KILOGRAMS_PER_POUND;
double metricHeight = heightInFeet * METERS_PER_FOOT;
// perform bmi calculation
double bmi = (int) (metricWeight / (metricHeight * metricHeight));
// display result
System.out.println("A person with");
System.out.println(" weight " + weightInPounds + " lbs");
System.out.println(" height " + heightInFeet + " feet");
System.out.println("has a BMI of " + bmi); }

4. Making BMI general purpose
Change
double weight = 75.5;
double height = 4.5; To
????

5. Making BMI general purpose
Change
double weight = 75.5;
double height = 4.5; To
Scanner stdin = new Scanner(System.in);
System.out.print("Enter weight (lbs): ");
double weight = stdin.nextDouble();
System.out.print("Enter height (feet): ");
double height = stdin.nextDouble();

6. public static void main(String[] args) {
// define constants
final double KILOGRAMS_PER_POUND = 0.454;
final double METERS_PER_FOOT = ;
// set up input acquistion
Scanner stdin = new Scanner(System.in);
// get person's characteristics
System.out.print("Enter weight (lbs): ");
double weight = stdin.nextDouble();
System.out.print("Enter height (feet): ");
double height = stdin.nextDouble();
// convert to metric equivalents
double metricWeight = weightInPounds * KILOGRAMS_PER_POUND;
double metricHeight = heightInFeet * METERS_PER_FOOT;
// perform bmi calculation
double bmi = (int) (metricWeight / (metricHeight * metricHeight));
// display result
System.out.println("A person with");
System.out.println(" weight " + weightInPounds + " lbs");
System.out.println(" height " + heightInFeet + " feet");
System.out.println("has a BMI of " + bmi); }

7. Can we display one place after the decimal?
Yes using a new out method named printf().

8. public static void main(String[] args) {
// define constants
final double KILOGRAMS_PER_POUND = 0.454;
final double METERS_PER_FOOT = ;
// set up input acquistion
Scanner stdin = new Scanner(System.in);
// get person's characteristics
System.out.print("Enter weight (lbs): ");
double weight = stdin.nextDouble();
System.out.print("Enter height (feet): ");
double height = stdin.nextDouble();
// convert to metric equivalents
double metricWeight = weightInPounds * KILOGRAMS_PER_POUND;
double metricHeight = heightInFeet * METERS_PER_FOOT;
// perform bmi calculation
double bmi = (int) (metricWeight / (metricHeight * metricHeight));
// display result
System.out.println("A person with");
System.out.println(" weight " + weightInPounds + " lbs");
System.out.println(" height " + heightInFeet + " feet");
System.out.printf("has a BMI of %4.1f“, bmi); }

9. Quick survey I am ok with Scanner and its methods Pretty much
With a little review, I’ll have it down
Not really
I’m so lost

10. Primitive variable assignment
Assignment operator =
Allows the memory location for a variable to be updated
Consider
int numberOfRabbits = 11;
numberOfRabbits = 121;
Besides signaling in a variable definition that the variable is to be initialized, the symbol = is also the Java assignment operator. The assignment operator takes two operands. The left operand is the target variable; the right operand is the modifying expression. When evaluated, the assignment operator updates the value in the memory location associated with a target variable based on the modifying expression.
The assignment operator works in the following manner. First, the left operand is evaluated to make sure that its value can be modified (e.g., a non-final variable). The right operand then is evaluated and its value is used to update the memory location associated with the left operand. For our particular assignment, the memory location associated with variable j is reset to the int value The assignment expression is read as “j gets 1985” or “j is assigned 1985.”

11. Primitive variable assignment
Assignment operator =
Allows the memory location for a variable to be updated
Consider
int numberOfRabbits = 11;
numberOfRabbits = 121;
Besides signaling in a variable definition that the variable is to be initialized, the symbol = is also the Java assignment operator. The assignment operator takes two operands. The left operand is the target variable; the right operand is the modifying expression. When evaluated, the assignment operator updates the value in the memory location associated with a target variable based on the modifying expression.
The assignment operator works in the following manner. First, the left operand is evaluated to make sure that its value can be modified (e.g., a non-final variable). The right operand then is evaluated and its value is used to update the memory location associated with the left operand. For our particular assignment, the memory location associated with variable j is reset to the int value The assignment expression is read as “j gets 1985” or “j is assigned 1985.”

12. Primitive variable assignment
Consider
int a = 1;
int aSquared = a * a;
a = 5;
aSquared = a * a;
int i = 0;
i = i + 1;
int asaRating;
asaRating = 400;

13. Primitive variable assignment
Consider
int a = 1;
int aSquared = a * a;
a = 5;
aSquared = a * a;
int i = 0;
i = i + 1;
int asaRating;
asaRating = 400;

14. Primitive variable assignment
Consider
int a = 1;
int aSquared = a * a;
a = 5;
aSquared = a * a;
int i = 0;
i = i + 1;
int asaRating;
asaRating = 400;

15. Primitive variable assignment
Consider
int a = 1;
int aSquared = a * a;
a = 5;
aSquared = a * a;
int i = 0;
i = i + 1;
int asaRating;
asaRating = 400;

16. Primitive variable assignment
Consider
int a = 1;
int aSquared = a * a;
a = 5;
aSquared = a * a;
int i = 0;
i = i + 1;
int asaRating;
asaRating = 400;

17. Primitive variable assignment
Consider
int a = 1;
int aSquared = a * a;
a = 5;
aSquared = a * a;
int i = 0;
i = i + 1;
int asaRating;
asaRating = 400;

18. Primitive variable assignment
Consider
int a = 1;
int aSquared = a * a;
a = 5;
aSquared = a * a;
int i = 0;
i = i + 1;
int asaRating;
asaRating = 400;

19. Primitive variable assignment
Consider
double x = 5.12;
double y = 19.28;
double rememberX = x;
x = y;
y = rememberX;

20. Primitive variable assignment
Consider
double x = 5.12;
double y = 19.28;
double rememberX = x;
x = y;
y = rememberX;

21. Primitive variable assignment
Consider
double x = 5.12;
double y = 19.28;
double rememberX = x;
x = y;
y = rememberX;

22. Primitive variable assignment
Consider
double x = 5.12;
double y = 19.28;
double rememberX = x;
x = y;
y = rememberX;

23. Primitive variable assignment
Consider
double x = 5.12;
double y = 19.28;
double rememberX = x;
x = y;
y = rememberX;

24. Quick survey
If I wanted to assign variable n the value of variable m I would do
n = m;
m = n;
int n = m;
int m = n;

25. Increment and decrement operators++
Increments a number variable by 1 --
Decrements a numeric variable by 1
Consider
int i = 4;
++i;
System.out.println(i);
System.out.print(++i);
System.out.println(i++);

26. Increment and decrement operators++
Increments a number variable by 1 --
Decrements a numeric variable by 1
Consider
int i = 4; // define
++i;
System.out.println(i);
System.out.print(++i);
System.out.println(i++);

27. Increment and decrement operators++
Increments a number variable by 1 --
Decrements a numeric variable by 1
Consider
int i = 4;
++i; // increment
System.out.println(i);
System.out.print(++i);
System.out.println(i++);

28. Increment and decrement operators++
Increments a number variable by 1 --
Decrements a numeric variable by 1
Consider
int i = 4;
++i;
System.out.println(i); // display
System.out.print(++i);
System.out.println(i++);
System.out.println(i); 5

29. Increment and decrement operators++
Increments a number variable by 1 --
Decrements a numeric variable by 1
Consider
int i = 4;
++i;
System.out.println(i);
System.out.print(++i); // update then display
System.out.println(i++);
5 6

30. Increment and decrement operators++
Increments a number variable by 1 --
Decrements a numeric variable by 1
Consider
int i = 4;
++i;
System.out.println(i);
System.out.print(++i);
System.out.println(i++); // update then display

31. Increment and decrement operators++
Increments a number variable by 1 --
Decrements a numeric variable by 1
Consider
int i = 4;
++i;
System.out.println(i);
System.out.print(++i);
System.out.println(i++);
System.out.println(i); // display

32. Question
Does the following statement compute the average of double variables a, b, and c? Why
double average = a + b + c / 3.0;

33. Expressions What is the value used to initialize expression
int expression = * 5;
What value is displayed
System.out.println(5 / 2.0);
Java rules in a nutshell
Each operator has a precedence level and an associativity
Operators with higher precedence are done first
* and / have higher precedence than + and -
Associativity indicates how to handle ties
When floating-point is used the result is floating point
It seems that there are two possible values for expr. If the addition is performed first, then expr is initialized to 30; if instead, the multiplication is performed first, then expr is initialized to 14. N

34. Question
Does the following statement compute the average of double variables a, b, and c? Why
double average = (a + b + c) / 3.0;

35. Escape sequences
Java provides escape sequences for printing special characters
\b backspace
\n newline
\t tab
\r carriage return
\\ backslash
\" double quote
\' single quote

36. Escape sequences What do these statements output?
System.out.println("Person\tHeight\tShoe size");
System.out.println("=========================");
System.out.println("Hannah\t5‘1\"\t7");
System.out.println("Jenna\t5'10\"\t9");
System.out.println("JJ\t6'1\"\t14");
Output
Person Height Shoe size
=========================
Hannah 5‘1" 7
Jenna 5'10" 9
JJ '1" 14