1. Maj Joel Young Joel.Young@afit.edu
Air Force Institute of Technology
Electrical and Computer Engineering
Object-Oriented Programming Topic 2: Fundamental Programming Structures in Java
Maj Joel Young
10-Apr-17
Maj Joel Young

2. Java Identifiers Identifiers
Used to name local variables
Names of attributes
Names of classes
Primitive Data Types Available in Java (size in bytes)
byte (1), -128 to 127
short (2), to 32767
int (4), to
long (8), to
float (4), -3.4E38 to 3.4E38, 7 digit precision
double (8), -1.7E308 to 1.7E308, 17 digits precision
char (2), unicode characters
boolean (true, false), discrete values

3. Java Identifiers Naming Rules Variables Must start with a letter
After first letter, can consist of letters, digits (0,1,…,9)
The underscore “_” and the dollar sign “$” are considered letters
Variables
All variables must be declared in Java
Can be declared almost anywhere (scope rules apply)
Variables have default initialization values
Integers: 0
Reals: 0.0
Boolean: False
Variables can be initialized in the declaration

4. Java Identifiers Example Declarations
int speed; // integer, defaults to 0
int speed = 100; // integer, init to 100
long distance = L; // “L” needed for a long
float delta = 25.67f; // “f” needed for a float
double delta = 25.67; // Defaults to double
double bigDelta = 67.8E200d; // “d” is optional here
boolean status; // defaults to “false”
boolean status = true;
Potential Problems (for the C/C++ crew)
long double delta = 3.67E204; // No “long double” in Java
unsigned int = ; // No unsigned ints in Java

5. Java Types Arrays int[] numbers = new int[n]
// Array of integers, size is n
size can be computed at run time, but can't be changed
allocated on heap (thus enabling run time size allocation)
invalid array accesses detected at run time (e.g. numbers[6];)
numbers.length; // read only variable specifying length of array
reference semantics
int[] winning_numbers;
winning_numbers = numbers; // refer to same array
numbers[0] = 13; // changes both

6. Java Types Strings String message = "Error " + errnum;
strings are immutable – can't be changed, although variables can be changed (and old string left for garbage collection)
message = "Next error " + errnum2;
use StringBuffer to edit strings
StringBuffer buf = new StringBuffer(greeting);
buf.setCharAt( 4, '?');
greeting = buf.toString();

7. Java Types Strings String comparison if (greeting == "hello" ) ….
// error, compares location only
if ( greeting.equals("hello")) …. // OK
string1.compareTo(string2)
// negative if string1 < string 2;
// zero when equal,
// positive if string1 > string2
string1.substring(2, 6);
// return substring between position 2 and 5

8. Java Operators Operators/Order of Precedence Operator Operation
() or [ ] or . or ++ or - -
Parens, array indices, object invocation, increment, decrement 1
+ or – or ~
Unary plus, unary minus, complement 2
* or / or %
Multiplication, division, modulus 3
+ or -
Addition, subtraction 4
<<,>>
Bitwise shifts 5
&
Bitwise AND 6 ^
Bitwise XOR 7 |
Bitwise OR 8

9. Java Operators Example Usage int anInt1 = 2, anInt2 = 1, anInt3;
double aDbl1;
anInt3 = anInt1 + anInt2 * 4; // anInt3 gets 6
anInt3 = (anInt1 + anInt2) * 4; // anInt3 gets 12
anInt3 = ++anInt2 * 2; // anInt3 gets 4
anInt2 = 1;
anInt3 = anInt2++ * 2; // anInt3 gets 2
anInt3 = anInt1 & anInt2; // anInt3 gets 0
anInt3 = anInt1 ^ anInt2; // anInt3 gets 3
anInt3 = anInt2 << 1; // anInt3 gets 2
anInt3 = 1 / 2; // anInt3 gets 0
aDbl1 = 1 / 2; // aDbl1 gets 0.0
aDbl1 = 1.0 / 2.0; // aDbl1 gets 0.5

10. Java Statements Import Statements (discussed later)
Class/Interface Declarations (discussed later)
Assignments
Conditionals
Loops
Miscellaneous (mixed in other discussions)

11. Java Statements Assignments General Format: variable = expression ;
Where variable is a previously declared identifier and
expression is a valid combo of identifiers, operators,
and method (a.k.a. procedure or function) calls
Shortcuts:
var *= expr ; // Equivalent to var = var * (expr);
var /= expr ; // Equivalent to var = var / (expr);
var += expr ; // Equivalent to var = var + (expr);
var -= expr ; // Equivalent to var = var – (expr);
var %= expr ; // Equivalent to var = var % (expr);
var++; // Equivalent to var = var + 1;
var--; // Equivalent to var = var - 1;

12. Java Conditional Constructs
“if” Statements
if with code block
if (boolean_expr) {
statements }
if with single statement
statement;

13. Java Conditional Constructs
if” Statements (Continued)
if-else
if (boolean_expr) {
statements for true }
else
statements for false if
statements
false
true

14. Java Conditional Constructs
Boolean Expressions
Boolean expressions use conditional operators such that they result in a value of true or false
Conditional Operators (Not by order of precedence)
Operator
Operation
== or !=
Equality, not equal
> or <
Greater than, less than
>= or <=
Greater than or equal, less than or equal !
Unary negation (NOT)
& or &&
Evaluation AND, short circuit AND
| or ||
Evaluation OR, short circuit OR

15. Java Conditional Constructs
Boolean Expression Examples
int i1 = 1, i2 = 2, i3 = 3, i4 = 0;
boolean b1 = true, b2 = false, b3 = true;
i2 > i1 // true
(i3 – i2) > i1 // false
(i3 – i2) >= i1 // true
(i2 > i1) & (i2 < i3) // true
(i2 < i1) | (i2 > i1) // true
i2 != i1 // true
(i1 < i2) | ((i1/i4) > 1) // Divide by 0 exception
(i1 < i2) || ((i1/i4) > 1) // true
(i1 < i2) | (i1++ > 1) // true, i1 contains 2
(i1 < i2) || (i1++ > 1) // true, i1 contains 1
b1 && b2 && b3 // false
(b1 || b2) && b3 // true
b1 && (i1 == (i3 – i2)) // true

16. Java Conditional Constructs
if-else” Statement Example if
statements
false
true
class Example {
static public void main(String args[])
// A very contrived example
int i1 = 1, i2 = 2;
System.out.print(“Result: “);
if (i1 > i2)
System.out.println(“i1 > i2”); }
else
System.out.println(“i2 >= i1”);

17. Java Conditional Constructs
The Switch Statement
switch (integer_expression) {
case int_value_1:
statements
break;
case int_value_2: …
case int_value_n:
default: } if
true
statements
false

18. Don’t forget the “break”
switch (integer_expression) {
case int_value_1:
statements
// No break!
case int_value_2:
break; …
case int_value_n:
default: } if
true
statements
false

19. Java Conditional Constructs
Example
int n = 5;
switch (n) {
case 1:
n = n + 1;
break;
case 5:
n = n + 2;
default:
n = n – 1; } if
true
statements
false

20. Java Conditional Constructs
Example
char c = ‘b’;
int n = 0;
switch (c) {
case ‘a’:
n = n + 1;
break;
case ‘b’:
n = n + 2;
default:
n = n – 1; } if
true
statements
false

21. Java Looping Constructs
while loop
Exit condition evaluated at top
do loop
Exit condition evaluated at bottom
for loop
Includes a initialization statements
Includes a update statements for each iteration

22. Java Looping Constructs
while loop
while (boolean_expr) {
statements }
do loop do if
statements
false
true if
statements
false
true

23. Java Looping Constructs
for loop
for (init_stmnt; bool_expr; update_stmnt) {
statements } if
statements
false
true
init
update

24. Java Looping Constructs
for loop
for (init_stmnt; bool_expr; update_stmnt) {
statements } if
statements
false
true
init
update

25. Java Looping Constructs
class Example {
static public void main(String args[])
int i = 0;
System.out.println("while loop");
while (i < 10)
System.out.println(i);
i++; }
System.out.println("do loop"); do
i--;
while (i > 0);
System.out.println("for loop");
for (i = 0; i < 10; i++)
} // End main
} // End Example

26. Homework Go to: http://developer.java.sun.com/developer/infodocs/
Explore the Java API Docs and Tutorials
Go to:
Explore:
Read the docs for the String class
Read the docs for the Integer class
Read the docs for the System class
Enter the code from the Example class (cut and paste from pdf or ppt) and compile and run it.