Introduction to Java Part 1 - Java

Note: These are notes from 4 years ago when I took Computer Science AB in school.

Identifiers:
-Start with a letter.
-Then letters, numbers or ‘_’
-No spaces
-No Reserved Words
-Case sensitive

Naming Conventions:
-Use names not letters (i.e. instead of ‘g’ we use ‘grade’)
-Variable start lowercase
--If more than one word, first word is not capitalized every word after that is (ex. studentGrade, studentInClass)
-Class start uppercase
-All capitals only used for constants (ex. PI)

Data Types:
int (integer)
-May not hold decimals. If an integer is assigned to ‘3.14’ the value will be displayed as ‘3’.
double (floating-point number)
-Larger in memory than an integer. May hold decimals or integers. If double is assigned to ‘3’ the value will be displayed as ‘3.0’.
char (character)
-Must be defined with quotes ‘’ around the value. (ex. ‘value’). Can hold any character on the keyboard.
boolean (true or false)
-Can only hold the value ‘true’ or ‘false’

Variables:
How to Declare and Assign Variables:

int grade; //declaration
grade = 11; //assignment
//or
int grade = 11; //combining declaration and assignment
//or
int a,b; //creates a integer ‘a’ and and integer ‘b’

int = variable type
grade = variable
value of grade = 11

Math Operators:
Computer knows order of operations.

double y = 7.0;
double answer;
answer = 3.0 + 5.0;
answer = y – 2.5;
answer = y * 3.2;
answer = y / 2.0;
/*‘answer’ would only equal the value of 3.5 The computer goes down the list and ignores previous assignments.*/ 

double a ,b = 5.0; //creates a blank double, ‘a’ and creates a double with the value of 5.0, ‘b’
int x = 2;
a = b / x;
a = 2.5
a = (int) b / x;
a = 2.0. 
/*This is because b is converted into an integer for this equation. 5/2, an integer/integer, will result in an integer answer. The real answer is 2.5 but it discards the decimal making it 2. a is a double however, so the value of a is 2.0*/

Modulus Operator = %
-Only works with integers

int a = 7;
int b = 2;
int c;
c = a % b;
c = 7 % 2
c = 1

Printing:

System.out.println ( “bla” ); //prints out “bla”
System.out.println ( c ); //prints out the value of the variable c
System.out.println ( “c = “ + c); //prints out “c = “ and the value of c

Assignment Operators:

int a = 7;
a = a + 5 //adds 5 to the value of a
a = 12