1. CIS3931 – Intro to JAVA
Lecture Note Set 2
17-May-05

2. Variables - Reminders Variables are Case-Sensitive
It must be a legal identifier
- May only begin with a letter, the
underscore or a dollar sign.
- Consist of letters, digits, underscores,
and the dollar sign.
- Must not start with a number!

3. Variables - Reminders
It must not be one of Java’s reserved keywords. (See Appendix C for a complete list)
It must not be a boolean literal – true or false
It must not be the reserved word null
It can be any length

4. Built-in Data Types char – used for storing single characters
boolean – has two possible values, true or false
Integer types:
- byte – 8 bits
- short – 16 bits
- int – 32 bits
- long – 64 bits

5. Data-Types continued Floating point types (for storing decimals)
- float – 32 bits
- double – 64 bits

6. Declaring Variables int x; //don’t forget the ; char grade = ‘A’;
You can also declare more than one variable in a line. Ex…
float x=3.4, y=9.7, z;
When declaring on one line, separate by a comma.

7. Control Structures
Provide a method by which you can test variables and conditions in your program
Provide a method of flow control and execution
if statements
if/else statements
while loops

8. Logical Operators Two types – Relational and Conditional
Relational : Compares two values and determines the relationship between them
Examples : > , < , >= , ==

9. Relationship operators
Use
Description
>
op1 > op2
Returns true if op1 is greater than op2
>=
op1 >= op2
Returns true if op1 is greater than or equal to op2
<
op1 < op2
Returns true if op1 is less than op2
<=
op1 <= op2
Returns true if op1 is less than or equal to op2 ==
op1 == op2
Returns true if op1 and op2 are equal !=
op1 != op2
Returns true if op1 and op2 are not equal

10. Conditional Operators
Used with relational operators
Combines multiple relational operators with a condition such as (and) or (or)

11. Conditional Operators
Use
Description
&&
Op1 && op2
Returns true if both op1 and op2 are true ||
Op1 || op2
Returns true if either op1 or op2 is true !
!op
Returns true if op is false

12. If statements Execute if the statement returns true int x = 5;
if (x == 5) {
System.out.print(“x = 5”); }
{ } are optional if only 1 line under if

13. If/Else The else executes only when the if statement fails.
if (x == 5)
System.out.println(“x=5”);
else
System.out.println(“x != 5”);

14. Dangling-else if (x > 5) if (y > 5)
System.out.println(“x and y are > 5”);
else
System.out.println(“x is <= 5”);
What is the output if…
x=10 and y=10? If x=10 and y=2?

15. Dangling Else p2 Compiler actually sees… if (x > 5) if (y > 5)
System.out.println(“x and y are > 5”);
else
System.out.println(“x is <= 5”);
To solve this problem, use { }

16. While Loops while executes until false. int product = 3;
while (product <= 100 )
product = 3 * product;
product is initially 3, then it goes to 9, 27, 81, 243. Once it gets to 243, it stops because 243 is not <= 100.

17. More while loops
{ } must be used after the while statement if there is more than 1 line.
While loops are extremely useful when you want to obtain correct input from the user.
Make user keep entering the information until it is correct.

18. Questions….