Nov 4, 2020 Notes

To Lecture Notes

IT 212 -- Nov 4, 2020

Zoom Poll 10

Take the Zoom Poll 10.
The correct answer is marked with *.
1. The Python script printname.py contains this single line:
```
print(__name__)
```
  What is the output when this script is run?
  a. main *b. __main__ c. printname
  d. printname.py e. __printname__
2. The Java class named Vehicle should be defined in a source code file with which name?
  a. Vehicle.class b. vehicle.class
  *c. Vehicle.java d. Vehicle.txt
3. Translate this Python statement into Java:
```
print(age)
```
  a. System.out.print(age); *b. System.out.println(age);
  c. System.print(age); d. System.println(age);
4. Translate this Python statement into Java:
```
print(age, end=' ')
```
  *a. System.out.print(age); b. System.out.println(age);
  c. System.print(age); d. System.println(age);
5. Translate this Python statement into Java:
```
n = 34.75
```
  *a. double n = 34.75; b. float n = 34.75;
  c. int = 34.75; d. n = Integer.parseInt(34.75);
6. Translate these Python statements into Java:
```
import sys
sys.exit( )
```
  a. System.exit( ); *b. System.exit(0);
  c. System.out.exit( ); d. System.out.exit(0);
7. Which symbol or symbols mark the beginning of a Java comment line?
  a. # b. % c. * *d. //
8. Which statement defined a Java object that reads lines from the keyboard like this:
```
String line = s.nextLine( );
```
  a. Scanner s = new Scanner("Keyboard");
  *b. Scanner s = new Scanner(System.in);
  c. Scanner s = Scanner("Keyboard");
  d. Scanner s = Scanner(System.in);
9. What are the delimiters for a Java block?
  a. [ ] *b. { } c. " "
  d. Like Python, Java uses indentation to indicate a block.
10. What is the first line of a Java main method?
  a. private static void main(String[ ] args) {
  b. private void static main(String[ ] args) {
  *c. public static void main(String[ ] args) {
  d. public void static main(String[ ] args) {

Java Primitive Datatypes

Unlike Python, not every datatype in Java is represented by a class.
A Java datatype that is not represented by a class is a primitive type.
These are the Java primitive types that we will use in IT 212:
```
int  double  char  boolean
```
Here are initialization statements for these four primitive types:
```
int n = 785;
double x = 31.928;
char c = 'A';
boolean b = true;
```

String Objects

A string in Java is not a primitive data type. It is an object instantiated from the system defined class String.

A string can be declared and initialized using long or short methods:

// Long method:
String s = new String("dog");

// Short method:
String s = "dog";

Practice Problems

Translate these Python code fragments into Java. Use this Java test class to test your translations:

public class TestClass {
    public static void main(String[ ] args) {
        System.out.println("This is a test.");
    }
}

# a.
print(a, " ", b)
print(str(a) + " " + str(b))
print(f"{a} {b}")
print("{0:s} {1:s}".format(a, b))

// Java Translation of #a:
// Only the second the fourth print statements
// can be translated into Java:
System.out.println(a + " " + b);
System.out.printf("%s %s\n", a, b);

# b.
print(str(a) + " " + str(b), end=" ")
print(a + b)

// Java Translation of #b:
System.out.print(a + " " + b + " ");
System.out.println(a + b);

# c.
gpa = input("Input GPA: ")
print("GPA: " + gpa);

// Java Translation of #c:
Scanner scanner = new Scanner(System.in);
System.out.print("Input GPA: ");
double gpa = Double.parseDouble(scanner.nextLine( ));
System.out.println("GPA: " + gpa);

# d.
x = a ** b

// Java Translation of #d:
x = Math.pow(a, b);

# e. (Python duck typing)
n = 5
p = 12.3456
x = 3.78e23
s = "abc"
b = True
c = '*'
print(n, p, x, s, b)

// Java Translation of #e:
int n = 5;
double p = 12.3456;
double x = 3.78e23;
String s = "abc";
boolean b = true;
System.out.println(String.format("%d %f %s %n %s %c", 
    n, p, x, s, b, c);

# f. 
import sys
sys.exit(1)

// Java translation of #f.
System.exit(1);

To obtain the error code output from
sys.exit or System.exit, enter this
line in the Command Prompt Window:
> echo %errorlevel%

To obtain the error code on a Mac
running Linux, ehter this line
in the Terminal Window:
> echo $?

# g.
n = 345
if n >= 1000:
    print("Large")
elif n >= 500:
    print("Medium")
else:
    print("Small")
    
# Java translation of #g:
int n = 345;
if (n >= 1000)
{
    print("Large")
else if n >= 500:
    print("Medium")
else:
    print("Small")

Java Control Structures

Look at these examples in the Java Control Stuctures section:
Overtime TempDesc
A Java for loop has this form:
```
         (1)           (2)        (3)
          |             |          |
          V             V          V
for(initialization; condition; iteration)
{
    action;
}
next statement;
```
(1) The initialization is performed once at the beginning of the loop.
(2) The condition is checked every time before the action is performed.
(3) If the condition is true, the action is performed;
if false, the loop terminates and the next statement after the end of the loop body is executed.
The iteration is performed at the end of the action but before the condition is checked.

Example:
```
for(int i = 1; i <= 100; i++)
{
    System.out.println(i);
}
```
This for loop prints the numbers from 1 to 100, one number per line.
Look at these examples:
CountTo100 CountDownBy7s

Project 4

Look at the Project 4 Description.
Write a simulation that rolls a pair of dice 3,600,000 times and records the number of times each total occurs. The range of possible totals on each roll is 2 to 12.