1. Program Elements
We can now examine the core elements of programming (as implemented in Java)
We focuse on:
data types
variable declaration and use, constants
operators and expressions
data conversion
syllabus
basic programming concepts
object oriented programming
topics in computer science

2. Data representation
question: how to represent information in the computer, using the java language?
answer: java lets us represent information in 8 different ways
these representation formats are called data types

3. Primitive Data Types
A data type is defined by a set of values and the operators you can perform on them
Each value stored in memory is associated with a particular data type; Java has several predefined types, called primitive data types
The following reserved words represent eight different primitive types:
byte, short, int, long
float, double
boolean
char

4. Integers
There are four separate integer primitive data types; they differ by the amount of memory used to store them
Type
byte
short
int
long
Storage
8 bits
16 bits
32 bits
64 bits
Min Value
-128
-32,768
-2,147,483,648
< -9 x 1018
Max Value
127
32,767
2,147,483,647
> 9 x 1018

5. reading from memory
תא 1: 1
תא 4: 

6. Floating Point There are two floating point types: Approximate
Min Value
-3.4 x 1038
-1.7 x 10308
Approximate
Max Value
3.4 x 1038
1.7 x 10308
Type
float
double
Storage
32 bits
64 bits

7. Characters
A char value stores a single character from the Unicode character set
A character set is an ordered list of characters
The Unicode character set uses 16 bits per character, allowing for 65,536 unique characters
It is an international character set, containing symbols and characters from many world languages

8. Characters
The ASCII character set is still the basis for many other programming languages
ASCII is a subset of Unicode, including:
uppercase letters
lowercase letters
punctuation
digits
special symbols
control characters
A B C …
a b c …
. , ; … …
& | \ …
carriage return, tab, ...

9. Boolean A boolean value represents a true/false condition.
It can also be used to represent any two states, such as a light bulb being on or off
The reserved words true and false are the only valid values for a boolean type
how many bytes does this datatype use?

10. Variables
A variable is an identifier (שם) that represents a storage in memory that holds a particular type of data
Variables must be declared before being used; the syntax of a variable declaration is:
data-type variable-name;
data type
variable name
int total;

11. variables in memory
תא 1: } 1
total
תא 4: 

12. Details of variable declaration
Multiple variables can be declared on the same line:
int total, count, sum;
Variables can be initialized (given an initial value) in the declaration:
int total = 0, count = 20;
double unitPrice = 57.25;

13. Variables use public static void main (String[] args) {
short weeks = 14;
int numberOfStudents = 120;
double averageFinalGrade = 78.6;
System.out.println(weeks);
System.out.println(numberOfStudents);
System.out.println(averageFinalGrade); }

14. Constants
A constant is similar to a variable except that it keeps the same value throughout its existence;
Constants are specified using the reserved word final
It is better to use constants than literals because:
They make the code more readable by giving meaning to a value
They facilitate change because the value is only specified in one place
Q: assembler languages do not have constants; what do we do?

15. Example - Constants use
// Reads the radius of a circle and prints
// its circumference and area
class ConstantsExample {
static final double PI = ;
public static void main(String[] args) {
double r, circumference, area;
System.out.println(“Enter radius: “);
r = EasyInput.readDouble ();
circumference = 2*PI*r;
area = PI*r*r;
System.out.println(“Circumference: “
+circumference);
System.out.println(“Area: “ + area); }

16. Assignment Statements
An assignment statement takes the following form:
variable-name = expression;
The expression is evaluated and the result is stored in the variable, overwriting the value currently stored in the variable

17. Assignment Statements: example
// Uses assignment to change a variable's value
public static void main (String[] args) {
int NumberOfStudents = 140;
System.out.println(“Students in 2001:”);
System.out.println(NumberOfStudents);
NumberOfStudents = 170;
System.out.println(" Students in 2000:”); }

18. Operators
An operator is a mapping that maps one or more values to a single value
examples: +, -, *, /
Java operators can be either:
Unary operators - takes a single value (e.g., -)
Binary operators - takes two values (e.g., +)
All Java binary operators are written in the infix notation:
operand1 operator operand2

19. Operators arithmetic increment and decrement logical assignment
conditional

20. Arithmetic operators
Java defines 5 arithmetic operators that are valid between every two numerical types
a + b add a and b
a - b subtract b from a
a * b multiply a and b
a / b divide a by b
a % b the remainder of dividing
a by b

21. Operators Operators can act differently on different data types
5.0 / 2.0
5 / 2.0
5.0 / 2
5 / 2
Essentially these are different operators
5.0 / 2.0
5 /
5.0 / 2
5 / 2
5.0 /
5 / 2.0
5.0 / 2
5 / 2
5.0 / 2.0
5 / 2.0
5.0 /
5 / 2
5.0 / 2.0
5 / 2.0
5.0 / 2
5 /

22. Expressions
An expression can consist of a combination of operators and operands
Operands can be literal values, variables, or expressions by themselves
Examples of expressions:
4 + 5
x * 2.73
a - (7 - b) x

23. Expression example public static void main (String[] args) {
int numberOfBooks = 30;
double bookPrice = 45.90;
double totalPrice;
totalPrice = numberOfBooks * bookPrice;
System.out.println(
“The total price is:”);
System.out.println(totalPrice); }

24. Operator Precedence
The order in which operands are evaluated in an expression is determined by a well-defined precedence hierarchy
Operators at the same level of precedence are evaluated according to their associativity (right to left or left to right)
Parentheses can be used to force precedence

25. Operator Precedence
Multiplication, division, and remainder have a higher precedence than addition and subtraction
Both groups associate left to right
Expression:
Order of evaluation:
Result:
/ % 3 3 1 4 2 6

26. Operator Precedence
What is the order of evaluation in the following expressions?
a + b + c + d + e
a + b * c - d / e 1 2 3 4 3 1 4 2
a / (b + c) - d % e 2 1 4 3
a / (b * (c + (d - e))) 4 3 2 1

27. Assignment Revisited
The assignment operator has a lower precedence than the arithmetic operators
First the expression on the right hand
side of the = operator is evaluated
answer = sum / 4 + MAX * lowest; 4 1 3 2
Then the result is stored in the
variable on the left hand side

28. Assignment Revisited
The right and left hand sides of an assignment statement can contain the same variable
First, one is added to the
original value of count
count = count + 1;
Then the result is stored back into count
(overwriting the original value)

29. String Concatenation
The ‘+’ operator between strings has the meaning of String concatenation
When we apply ‘+’ upon a String and a value of another type, that value is first converted into a String and the result is the concatenation of the two Strings

30. String Concatenation Output: public static void main(String[] args) {
System.out.print(“The international “
+ “dialing code”);
System.out.println(“for Israel is “
+ 972); }
Output:
The international dialog code for Israel is 972

31. Data Conversions
Sometimes it is convenient to convert data from one type to another; e.g., we may want to treat an integer as a floating point value during a computation
Conversions must be handled carefully to avoid losing information:
Widening conversions are safest because they tend to go from a specific data type to a general one (such as int to float)
Narrowing conversions can lose information because they tend to go from a general data type to a more specific one (such as float to int)

32. Data Conversions In Java, data conversions can occur in three ways:
Assignment conversion occurs when a value of one type is assigned to a variable of another; only widening conversions can happen via assignment
Arithmetic promotion happens automatically when operators in expressions convert their operands
Casting

33. Data Conversions: casting
Casting is the most powerful, and dangerous, technique for conversion
Both widening and narrowing conversions can be accomplished by explicitly casting a value
To cast, the type is put in parentheses in front of the value being converted
int total, count;
result = (float) total / count;

34. The Increment and Decrement Operators
The increment operator (++) adds one to its integer or floating point operand
The decrement operator (--) subtracts one
The statement
count++;
is essentially equivalent to
count = count + 1;

35. The Increment and Decrement Operators
The increment and decrement operators can be applied in prefix (before the variable) or postfix (after the variable) form
When used alone in a statement, the prefix and postfix forms are basically equivalent. That is,
count++;
is equivalent to
++count;

36. The Increment and Decrement Operators
When used in a larger expression, the prefix and postfix forms have a different effect
In both cases the variable is incremented (decremented)
But the value used in the larger expression depends on the form
Expression
count++
++count
count--
--count
Operation
add 1
subtract 1
Value of Expression
old value
new value

37. The Increment and Decrement Operators
If count currently contains 45, then
total = count++;
assigns 45 to total and 46 to count
total = ++count;
assigns the value 46 to both total and count

38. The Increment and Decrement Operators
If sum contains 25, then the statement
System.out.println (sum++ + " " +
++sum + " " + sum + " " +
sum--);
prints the following result:
and sum contains after the line is complete 25 27 27 27 26

39. Assignment Operators
Often we perform an operation on a variable, then store the result back into that variable
Java provides assignment operators that simplify that process
For example, the statement
sum += value;
is equivalent to
sum = sum + value;

40. Assignment Operators
There are many such assignment operators, always written as op= , such as:
Operator += -= *= /= %=
Example
x += y
x -= y
x *= y
x /= y
x %= y
Equivalent To
x = x + y
x = x - y
x = x * y
x = x / y
x = x % y

41. Assignment Operators
The right hand side of an assignment operator can be a complete expression
The entire right-hand expression is evaluated first, then combined with the additional operation
Therefore
result /= (total-MIN) % n;
is equivalent to
result = result /
((total-MIN) % n);

42. How many different ways to do...
int x=0,y=0;
 x=1; y=2;
int x=1;y=1;
 x=2; y=2;

43. What you should be able to do...
write programs which have variables
perform simple arithmetic operations and store the output value for further use