Java-Net Beans IDE- Programming Fundamentals
Tokens
Smallest element of the program known as tokens. They are as
follows:
a)
Variables/Identifiers
b)
Literals
c)
Separators/Punctuations
d)
Keywords/Reserved
Words
e)
Operators
Variables/Identifiers
A variable
is an identifier that denotes a storage location used to store a data value.
Unlike constants that remain unchanged during the execution of a program, a
variable may take different values at different times during the execution of
the program. Or variable
is a named storage location in computer memory whose contents can change during
a program run.
A
variable name can be chosen by the programmer in a meaningful way so as to
reflect what it represents in the program.
- Upper case and Lower case are distinct. This means that the variable total is not ‘equal’ to ‘TOTAL’
§ An identifier is a series of characters consisting of
letters, digits, underscore (_) and dollar sign ($) that does not begin with a
digit and does not contain any space.
§ Must begin with a letter, dollar sign, or an underscore
§ Are case sensitive
§ Keywords or reserved words can not be used as variable name
Data_type
variable_name1, variable_name2; OR
Data_type
variable_name1=default value;
Variables can be of
following types:
Local Variables: The scope of the local variables is
limited to the code level in which they are declared.
Global Variables: Global variables can be referred
to anywhere in the code, within any function, whenever it is after its
declaration.
Scope of a Variable:
The
part of program where a variable is usable is called scope of a variable.
Constants/Literals
Constants
are the fixed value that never change their values during program execution.
final double
pi=3.14;
Seprators
There are
few characters that are used as seperators.
( ) { } [ ] ; , .
Keywords/Reserved
Words
There are some words in
Java which have pre-defined meaning to compiler. They implement specific
features of the language. Some commonly used keywords are |
abstract
|
generic
|
super
|
const
|
native
|
var
|
|
float
|
return
|
catch
|
int
|
transient
|
false
|
|
protected
|
byvalue
|
import
|
threadsafe
|
double
|
outer
|
|
boolean
|
goto
|
switch
|
continue
|
new
|
void
|
|
for
|
short
|
char
|
interface
|
true
|
final
|
|
public
|
case
|
inner
|
throw
|
else
|
package
|
|
break
|
if
|
synchronized
|
default
|
null
|
volatile
|
|
future
|
static
|
class
|
long
|
try
|
finally
|
|
rest
|
cast
|
instanceof
|
throws
|
extends
|
private
|
|
byte
|
implements
|
this
|
do
|
operator
|
while
|
OPERATORS
Operators are the special
symbol that performs a particular function on operands. Operators are used in
programs to manipulate data and variables. Java operators can be classified
into a number of related categories as below:
Arithmetic operators
Arithmetic operators are
defined for both integer and floating point numeric types
|
Operators
|
Meaning
|
Example
|
Result
|
|
+
|
Addition
|
5 + 4
|
9
|
|
_
|
Subtraction
|
5 - 4
|
1
|
|
*
|
Multiplication
|
5 * 4
|
20
|
|
/
|
Division
|
5 / 2
|
2
|
|
%
|
Modulus/ Remainder
|
5 % 2
|
1
|
Relational/Comparison
operators
Relational operators in
java are used to compare two or more variables or constants. All relational
operators are Binary Operators, and their operands are numeric
expressions.
Operators
|
Description
|
|
= =
|
Equals to
|
|
>
|
Greater than
|
|
<
|
Less than
|
|
>=
|
Greater than equal to
|
|
<=
|
Less than equal to
|
|
!=
|
Not equal to
|
Logical operators
These operators are used
to combine one or more than one relational expressions. By combining logical
operators with relational operators. These operators operate on boolean values
|
Operators
|
Description
|
|
&
|
Logical AND
|
|
&&
|
Conditional AND
|
|
|
|
OR
|
|
||
|
Conditional OR
|
|
!
|
Logical negation (NOT)
|
Assignment operators (=)
e.g. int y =2;
e.g double x;
int y;
x = y; (in this case the value of y is converted into
type double, and assign to x)
Unary operators(+, -)
Java provides two unary
operators for which only one variable is required.
e.g. a = -10; b = +20; c = -a; d = + b;
Increment/decrement operators
(++, --)
++ or – adds 1 to its
operands subtracts 1
a
= a + 1; (is the same as ++a; or
a++;)
a = a – 1 (is
the same as --a; or a--;)
prefix (++a, --a): these operators follow Change
then use
postfix(a++, a--):these operators follow Use
then Change
e.g
Evaluate x = ++y +2 y if y
=6
= 7 + 2 * 7
= 21
Conditional/ternary
operators (? :)
It requires three operands. The conditional operator is
used to replace if – else logic. The syntax of conditional operator is:
Condition ? Statement1 : Statement2;
If the condition evaluates
true then the statement1 is evaluated else statement2 is evaluated
e.g. x = 10;
y = 15;
z = (x > y)? x : y;
Order of precedence
If two or more operators
are used in an expression, and if there are no parentheses to indicate the
order in which the operators are to be evaluated, then the computer needs some
way of deciding which operator to evaluate first
|
Order
|
Operators
|
|
First
|
* / %
|
|
Second
|
+ -
|
e.g (1) 8
+ 4 * 6 – 8 / 4
8 + 24 – 8 / 4
8 + 24 -2
32 - 2
30
Data
Types
Every
variable in Java has a data type. Data type specifies the size and type of
value that can be stored. Data types are used to identify the type of data.
There are two categories of data type into which data types have been divided:
PRIMITIVE
TYPES REFERENCE
TYPES
integers
(byte, short, int, long) classes, arrays, interfaces
floating
point numbers(float, double)
boolean (true/false)
character
(char)
|
Type
|
Storage
|
Range
|
|
boolean
|
1 bit
|
True or false
|
|
byte
|
8 bits
|
-128 to –127
|
|
short
|
16 bits
|
-32768 to 32767
|
|
char
|
16 bits (2bytes)
|
0 to 65536
|
|
int
|
32 bits
|
-2147483648 to 2147483647
|
|
long
|
64 bits
|
-9223372036854775808 to
9223372036854775807
|
|
float
|
32 bits (4 bytes)
|
-3.4 E + 38 to 3.4 E + 38
|
|
double
|
64 bits
|
-1.7 E + 308 to 1.7 E + 308
|
Strings
String
represents a sequence of character. The easiest way to represent a sequence of
character.
Note:
Java strings can be connected using the ‘+’ operator
Expression
An expression is a formula consisting of one or more operands
and zero or more operators linked together to compute a value.
Blocks
A group
of statement enclosed in pair of parenthesis {} is called block or a compound
statement
{
statements
}
Comments
Comments are the lines in the source
code that are ignored by the compiler at during execution of the program. It
enhances the readability to the programmer .Comments can be of two types
Single
line comment e.g. //
Multiline
Comment e.g. /* …………………..
…………………….*/
Type
casting/Conversion
Type casting is a way to convert a variable from one data
type to another data type. For example, if you want to store a long value into
a simple integer then you can type cast long to int. You can convert values
from one type to another explicitly using the cast operator as follows:
(type_name) expression
To assign a value of one type to a variable of another type.
If the two types are compatible, then Java will perform the conversion
automatically. For example, it is always possible to assign an int value to a
long variable.
When one type of data is assigned to another type of
variable, an automatic conversion will take place if the following two
conditions are met:
Ø The two types are compatible
Ø The destination type is larger than the
source type
Java provides two types of conversion-
(1)
Implicit Conversion: The
conversion performed by the compiler automatically is called implicit
conversion
e.g int
x=5
float
y=3.5, z;
z=x
+ y;
(2) Explicit Conversion (Type Casting): The conversion performed by the user according to their
requirements is called explicit conversion
e.g int x=5, y=2;
float
z;
z
= (float)x / y;
Numeric
types are not compatible with char or boolean and char and boolean are not
comptible with each other.
Library
A library is
a set of readymade classes available with java. A programmer is just required
to import (include in the program) a library and simple use the associated
classes. e.g. import java.io.*
Using
JOptionPane to Display a Message
You use the JOptionPane class's showMessageDialog method to display a message. The
message type argument can be assigned one of these:
- JOptionPane.ERROR_MESSAGE
- JOptionPane.INFORMATION_MESSAGE
- JOptionPane.WARNING_MESSAGE
- JOptionPane.QUESTION_MESSAGE
- JOptionPane.PLAIN_MESSAGE (no icon will be used)
For
example, the following code displays four different JOptionPane dialogs.
JOptionPane.showMessageDialog(null,"Message","Title",JOptionPane.INFORMATION_MESSAGE);
JOptionPane.showMessageDialog(null,"Message","Title",JOptionPane.WARNING_MESSAGE);
JOptionPane.showMessageDialog(null,"Message","Title", JOptionPane.ERROR_MESSAGE);
Using Input Dialogs
String input = JOptionPane.showInputDialog("Enter Input:");System.out.println(input);
Commonly available
Swing Controls in Java
jFrame:
A Frame is a container control, in which all the controls
can be place.
jLabel:
JLable allows placing un-editable text on the Frame/Panel during run time
jTextField:
JTextFiled allows placing editable text on the
Frame/Pane. User can enter text in a textField during runtime.
jbutton:
is used to initiate an action when it is clicked.
jList:
is a group of values or items from which one or more
selections can be made.
jComboBox:
jComboBox is similar to jList but also allow to enter
editable text during run time. It is a combination of jTextFiled and jList.
jPanel:
Act like a frame, to group one or more controls.
jRadioButton:
Allow us to choose a single item from a group of jRadioButton options.
jCheckBox:
Allow us to choose one or more items from a group of
jCheckBox options.
jPasswordField:
Allow us to enter a text during the run time but shows an
encrypted text instead of the original text
jTextArea:
JTextArea is a multi-line text component to
enter or edit text.
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