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Friday, August 5, 2016

Variables and Java Operators

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

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