Download Lesson 2

Java Programming
Lesson 2
Lesson 2
Variables, Expression
Java identifier
Java identifier is a name consisting of letters and digits, the first character must be a
letter, and you can use _, $. Most Java programmers don’t use underscores, instead
initiate each interior word with an upper case character. They also start class name
with uppercase and methods with small letters. (speed_of_light, SpeedOfLight).
Java data Types
1- Numeric
Integer
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Real
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2- Non-numeric
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byte: 1 byte: -128 to 127
short: 2 byte
int: 4 byte
long: 8 byte
float: 4 bytes
double: 8 byte
char: 2 byte
String
boolean
Note: Java defines the exact sizes of its simple data type and these sizes are
guaranteed to be the same on any computer that can run Java byte code.
Assignment
Assignment operator in Java is =
To declare a variable:
Syntax: Data-type variable-list separated by comma and may have initial values;
Ex: int a, b, c =10, d;
A compilation error may be generated If you use any variable before initialization.
Comments
// For single line
/* For multiple lines *//
Print statement
To print any thing on the screen, use System.out.println. Ex:
System.out.println (“ the value of a =”);
System.out.println ( a ) ;
or
System.out.println (“ the value of a =”+ a);
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Java Programming
Lesson 2
Note: println method can take only one argument. In order to print more than one
argument use + operator to concate the argument’s values.
Java literal
Boolean literal: true, false.
String literal: “”
Character literal: ‘ ‘. char c1 = ‘A’, c2 = 65;
Numerical literal:
Integer
int (default)
long (…l)
Real
double (default, …d)
float (…f)
Note:
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Hexadecimal values start with 0x. Octal values starts with 0. Ex: 0x10L.
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Real could have dot representation or scientific representation.
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Controls code:
\n: new line
\t: tab
\\: backslash
\’: single quote
\”: double quote
\nnn: char with nnn Unicode in octal system.
\unnnn : char with nnnn Unicode represented in hexadecimal code, Ex: char
c = ‘\u0037’
Assignments Rules:
1.
Var1 = var2; Var1 must be the same type as var2 or greater (ex: int = int or
short or byte;)
2.
Var1 = literal;
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For int values: as long as the values are in the proper range, Java can
convert them to the desired type. Ex: (b = 10; ok. b = 200 is not ok).
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For long literal: can be assigned only to long or float or double. Even if
they are two small. Ex: (i = 1L is not ok).
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for float: float = float literal
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For double: double = double or float literal.
Read Statements
import java.io.*; // at the beginning of the file.
public class Class1
{public static void main (String[] args) throws Exception
{
BufferedReader var = new BufferedReader ( new
InputStreamReader(System.in));
String s = var.readLine();
Int I = Integer.parseInt(I);
}}
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Java Programming
Lesson 2
Operators: +, -, *, /, %, ++, --, op =
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Integer Division: int / int
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Modules: %: int % int: return the remainder. While Real % Real return the
remainder fraction. Ex:
double d1 =7.6, d2 = 7 ;
d2 = d1 % d2 ; // d2 = 0.6
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Increment Operator:
Ex:
int j ,i = 100;
j = i ++; // j = 100 , i=101
j = ++i; // j = 101 , i= 102
Ex:
int i = 255;
System.out.println (i++ +”” + ++i); // 255 257
Note: any expression returns a value (System.out.println (b=3); // return 3).
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Op =
Var1 = var1 op var2 is equivalent to var1 op= var2
Ex: count = count +k; is equivalent to count += k;
Ex :
double R ;
R =7.6 ;
System.out.println (++R); // 8.6
Assignment:
Rule: The destination should be as the large as the largest operand in order
to hold the result. Ex: float = int + byte + float // or double
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Rule: if any value in integer expression is of type long then the result is
long. Else the result is always int.
Ex:
byte b1= 1 , b2 = 2 ,b3;
b3 = b1 + b2 ; // not ok
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Type casting
If you want to tell Java to convert value from one type to another type use casting
(prefix the value or the expression with the new type) .
Ex:
long l;
int i;
l = 10 ; // ok
i = l ; // not ok
i = (int) l; // it’s now your responsibility to ensure the validation.
Ex:
byte b1 =1 , b2 =2 ,b3;
b3 = b1 + b2 ; // not correct
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Java Programming
Lesson 2
b3 = (byte) (b1+b2) ; // correct
Ex:
int R;
double v = 4.99;
R = (int) v; // R = 4 truncated
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Precedence Rule < abbreviated >
(), [ ] , dot
! , ++, --, new
*, /, %
+, < ,<= ,> , >=
== , !=
&&
||
=, op=
Q: what is the value of x and y in the following expression: x = y =5;
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