1 - Java variable
The type of each variable Java must be declared at the start, then we say that Java is strongly typed. There are 8 primitive types (predefined) in java.
6 numeric types → 4 Integers types + 2 floating types
1 boolean type → boolean values (true or false)
1 char type → Unicode encoding
1.1 - Integer type
– int : -214 783 648 à 214 783 647
– short : -32 768 à 32767
– long : -9 223 372 036 854 775 808 à 9 223 372 036 854 775 807
– byte : -128 à 127
1.2 - Floating type
– float : Around of 2 billion (6 or 7 digits)
– double : 15 digits
1.3 - Java variabl declaration
Java requires that each variable must be declared,failing which the compiler displays an error message. To declare a variable just type its name preceded by its type.
Example
int n ; // declare a variable of integer type
byte b ; // declare a variable of byte type
int i, j ; // declare two variables of integer type
2.4 - Variable initialization and assignement
Each declared variable can be followeb by it's value, this value is called initial value.
Example
int n ; // declare a variable of integer type
n = 10 ; // assignement value of variable
// or simply :
int i = 10 ; // declare a variable of integer type and assignment value of variable
2 - Java operators
2.1 - The arithmetic's operators :
The usual arithmetic operators are:
- "+" Addition
- "*" Multiplication
- "-" Subtraction
- "/" Division
Example
int n = 9;
int m = 3 * n; // the value of m is 27
// To simplify the writing we use the notations:
x + = 2 // to denote x = x + 2
x * = 3 // to denote x = x * 3
2.2 - Increment / decrement operators
Java is endowed with the increments operators
- x++ adds 1 to the value x ( this operation is called the incrementation )
- x- substract 1 to the value of x ( this operation is called the decrementation )
Example
int x = 10;
x ++; // gives x the value 11
Double y = 33.77; // gives y the value 32.77
2.3 - Relational and Booleans operators
- == : Equality test
- ! = : Different
- > = : Greater than or equal
- <= : Less than or equal
- > : Higher
- < : lower
- && : "and" Logic
- || : "Or" logic
