Air Force Institute of Technology
Electrical and Computer Engineering
Object-Oriented Programming
Topic 2:
Fundamental Programming
Structures in Java
Maj Joel Young
Joel.Young@afit.edu
13-Apr-15
Maj Joel Young
Object-Oriented
Programming
Design
Java Identifiers
• Identifiers
– Used to name local variables
– Names of attributes
– Names of classes
• Primitive Data Types Available in Java (size in bytes)
–
–
–
–
–
–
–
–
13-Apr-15
byte (1), -128 to 127
short (2), -32768 to 32767
int (4), -2147483648 to 2147483647
long (8), -9223372036854775808 to 9223372036854775807
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
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Electrical and Computer Engineering
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Object-Oriented
Programming
Design
Java Identifiers
• Naming Rules
– 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
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Electrical and Computer Engineering
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Object-Oriented
Programming
Design
Java Identifiers
• Example Declarations
int speed;
int speed = 100;
long distance = 3000000000L;
float delta = 25.67f;
double delta = 25.67;
double bigDelta = 67.8E200d;
boolean status;
boolean status = true;
//
//
//
//
//
//
//
integer, defaults to 0
integer, init to 100
“L” needed for a long
“f” needed for a float
Defaults to double
“d” is optional here
defaults to “false”
• Potential Problems (for the C/C++ crew)
long double delta = 3.67E204; // No “long double” in Java
unsigned int = 4025890231;
// No unsigned ints in Java
13-Apr-15
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Electrical and Computer Engineering
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Object-Oriented
Programming
Design
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
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Electrical and Computer Engineering
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Object-Oriented
Programming
Design
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();
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Electrical and Computer Engineering
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Object-Oriented
Programming
Design
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
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Electrical and Computer Engineering
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Object-Oriented
Programming
Design
Java Operators
• Operators/Order of Precedence
Operator
() or [ ] or . or ++ or - -
13-Apr-15
Operation
Precedence
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
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Electrical and Computer Engineering
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Object-Oriented
Programming
Design
Java Operators
• Example Usage
int anInt1 = 2, anInt2 = 1, anInt3;
double aDbl1;
anInt3 = anInt1 + anInt2 * 4;
anInt3 = (anInt1 + anInt2) * 4;
anInt3 = ++anInt2 * 2;
anInt2 = 1;
anInt3 = anInt2++ * 2;
anInt2 = 1;
anInt3 = anInt1 & anInt2;
anInt3 = anInt1 ^ anInt2;
anInt3 = anInt2 << 1;
anInt3 = 1 / 2;
aDbl1 = 1 / 2;
aDbl1 = 1.0 / 2.0;
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Air Force Institute of Technology
Electrical and Computer Engineering
// anInt3 gets 6
// anInt3 gets 12
// anInt3 gets 4
// anInt3 gets 2
//
//
//
//
//
//
anInt3 gets 0
anInt3 gets 3
anInt3 gets 2
anInt3 gets 0
aDbl1 gets 0.0
aDbl1 gets 0.5
9
Object-Oriented
Programming
Design
Java Statements
• Import Statements (discussed later)
• Class/Interface Declarations (discussed later)
• Assignments
• Conditionals
• Loops
• Miscellaneous (mixed in other discussions)
13-Apr-15
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Electrical and Computer Engineering
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Object-Oriented
Programming
Design
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
var /= expr
var += expr
var -= expr
var %= expr
var++;
var--;
13-Apr-15
; // Equivalent to
; // Equivalent to
; // Equivalent to
; // Equivalent to
; // Equivalent to
// Equivalent to
// Equivalent to
var
var
var
var
var
var
var
Air Force Institute of Technology
Electrical and Computer Engineering
=
=
=
=
=
=
=
var
var
var
var
var
var
var
*
/
+
–
%
+
-
(expr);
(expr);
(expr);
(expr);
(expr);
1;
1;
11
Object-Oriented
Programming
Design
Java Conditional Constructs
• “if” Statements
– if with code block
if (boolean_expr)
{
statements
}
– if with single statement
if (boolean_expr)
statement;
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Electrical and Computer Engineering
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Object-Oriented
Programming
Design
Java Conditional Constructs
• if” Statements (Continued)
– if-else
if (boolean_expr)
{
statements for true
}
else
{
statements for false
}
13-Apr-15
if
true
statements
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Electrical and Computer Engineering
false
statements
13
Object-Oriented
Programming
Design
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
== or !=
> or <
>= or <=
!
& or &&
| or ||
13-Apr-15
Operation
Equality, not equal
Greater than, less than
Greater than or equal, less than or equal
Unary negation (NOT)
Evaluation AND, short circuit AND
Evaluation OR, short circuit OR
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Electrical and Computer Engineering
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Object-Oriented
Programming
Design
Java Conditional Constructs
• Boolean Expression Examples
int i1 = 1, i2 = 2, i3 = 3, i4 = 0;
boolean b1 = true, b2 = false, b3 = true;
i2 > i1
(i3 – i2) > i1
(i3 – i2) >= i1
(i2 > i1) & (i2 < i3)
(i2 < i1) | (i2 > i1)
i2 != i1
(i1 < i2) | ((i1/i4) > 1)
(i1 < i2) || ((i1/i4) > 1)
(i1 < i2) | (i1++ > 1)
(i1 < i2) || (i1++ > 1)
b1 && b2 && b3
(b1 || b2) && b3
b1 && (i1 == (i3 – i2))
13-Apr-15
//
//
//
//
//
//
//
//
//
//
//
//
//
true
false
true
true
true
true
Divide by 0 exception
true
true, i1 contains 2
true, i1 contains 1
false
true
true
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Electrical and Computer Engineering
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Object-Oriented
Programming
Design
Java Conditional Constructs
• if-else” Statement Example
class Example
{
static public void main(String args[]) true
{
// A very contrived example
int i1 = 1, i2 = 2;
statements
System.out.print(“Result: “);
if (i1 > i2)
{
System.out.println(“i1 > i2”);
}
else
{
System.out.println(“i2 >= i1”);
}
}
}
13-Apr-15
Air Force Institute of Technology
Electrical and Computer Engineering
if
false
statements
16
Object-Oriented
Programming
Design
Java Conditional Constructs
• The Switch Statement
switch (integer_expression)
{
case int_value_1:
statements
break;
case int_value_2:
statements
break;
…
case int_value_n:
statements
break;
default:
statements
}
13-Apr-15
Air Force Institute of Technology
Electrical and Computer Engineering
if
true
statements
false
if
true
statements
false
if
true
statements
false
statements
17
Object-Oriented
Programming
Design
• Don’t forget the “break”
switch (integer_expression)
{
case int_value_1:
statements
// No break!
case int_value_2:
statements
break;
…
case int_value_n:
statements
break;
default:
statements
}
13-Apr-15
Air Force Institute of Technology
Electrical and Computer Engineering
if
true
statements
false
if
true
statements
false
if
true
statements
false
statements
18
Object-Oriented
Programming
Design
Java Conditional Constructs
• Example
int n = 5;
switch (n)
{
case 1:
n = n + 1;
break;
case 5:
n = n + 2;
break;
default:
n = n – 1;
}
13-Apr-15
Air Force Institute of Technology
Electrical and Computer Engineering
if
true
statements
false
if
true
statements
false
statements
19
Object-Oriented
Programming
Design
Java Conditional Constructs
• Example
char c = ‘b’;
int n = 0;
switch (c)
{
case ‘a’:
n = n + 1;
break;
case ‘b’:
n = n + 2;
break;
default:
n = n – 1;
}
13-Apr-15
Air Force Institute of Technology
Electrical and Computer Engineering
if
true
statements
false
if
true
statements
false
statements
20
Object-Oriented
Programming
Design
Java Looping Constructs
• while loop
– Exit condition evaluated at top
• do loop
– Exit condition evaluated at bottom
• for loop
– Exit condition evaluated at top
– Includes a initialization statements
– Includes a update statements for each iteration
13-Apr-15
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Electrical and Computer Engineering
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Object-Oriented
Programming
Design
Java Looping Constructs
• while loop
false
while (boolean_expr)
{
statements
}
if
true
statements
–
• do loop
statements
do
{
statements
}
while (boolean_expr)
13-Apr-15
Air Force Institute of Technology
Electrical and Computer Engineering
if
true
false
22
Object-Oriented
Programming
Design
Java Looping Constructs
• for loop
for (init_stmnt; bool_expr; update_stmnt)
{
statements
init
}
false
if
true
statements
13-Apr-15
Air Force Institute of Technology
Electrical and Computer Engineering
update
23
Object-Oriented
Programming
Design
Java Looping Constructs
• for loop
for (init_stmnt; bool_expr; update_stmnt)
{
statements
init
}
false
if
true
statements
13-Apr-15
Air Force Institute of Technology
Electrical and Computer Engineering
update
24
Object-Oriented
Programming
Design
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
{
System.out.println(i);
i--;
}
while (i > 0);
System.out.println("for loop");
for (i = 0; i < 10; i++)
{
System.out.println(i);
}
} // End main
} // End Example
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Electrical and Computer Engineering
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Object-Oriented
Programming
Design
Homework
• Go to: http://developer.java.sun.com/developer/infodocs/
– Explore the Java API Docs and Tutorials
• Go to: http://java.sun.com/j2se/1.4.2/docs/api/
– 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.
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Electrical and Computer Engineering
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