TOKENS
Introduction:
A Java program is basically a set of
classes. A class is defined by a set of declaration statements and methods or
functions. Most statements contain expressions, which express the actions
carried out on information or data. Smallest individual thing in a program are
known as tokens. The compiler recognizes them for building up expression and
statements.
Tokens in Java:
There are five types of token as
follows:
1. Literals
2. Identifiers
3. Operators
4. Separators
Literals:
Literals in Java are a sequence of
characters (digits, letters and other characters) that characterize constant
values to be stored in variables. Java language specifies five major types of
literals are as follows:
1. Integer literals
2. Floating point literals
3. Character literals
4. String literals
5. Boolean literals
Identifiers:
Identifiers are programmer-created
tokens. They are used for naming classes, methods, variables, objects, labels,
packages and interfaces in a program. Java identifiers follow the following
rules:
1. They can have alphabets, digits, and the underscore
and dollar sign characters.
2. They must not start with a digit.
3. Uppercase and lowercase letters are individual.
4. They can be of any length.
Identifier must be meaningful, easily
understandable and descriptive.
For example:
Private and local variables like “length”.
Name of public methods and instance
variables begin with lowercase letter like “addition”.
Keywords:
Keywords are important part of Java.
Java language has reserved 50 words as keywords. Keywords have specific meaning
in Java. We cannot use them as variable, classes and method. Following table
shows keywords.
|
abstract
|
char
|
catch
|
boolean
|
|
default
|
finally
|
do
|
implements
|
|
if
|
long
|
throw
|
private
|
|
package
|
static
|
break
|
double
|
|
this
|
volatile
|
import
|
protected
|
|
class
|
throws
|
byte
|
else
|
|
float
|
final
|
public
|
transient
|
|
native
|
instanceof
|
case
|
extends
|
|
int
|
null
|
const
|
new
|
Operator:
Java carries a broad range of
operators. An operator is symbols that specify operation to be performed may be
certain mathematical and logical operation. Operators are used in programs to
operate data and variables. They frequently form a part of mathematical or
logical expressions.
Categories of operators are as
follows:
1. Arithmetic operators
2. Logical operators
3. Relational operators
4. Assignment operators
5. Conditional operators
6. Increment and decrement operators
7. Bit wise operators
Arithmetic operators:
Arithmetic operators are used to make
mathematical expressions and the working out as same in algebra. Java provides
the fundamental arithmetic operators. These can operate on built in data type
of Java.
Following table shows the details of
operators.
|
Operator
|
Importance/ significance
|
|
+
|
Addition
|
|
-
|
Subtraction
|
|
/
|
Division
|
|
*
|
Multiplication
|
|
%
|
Modulo division or remainder
|
“+” operator in Java:
In this program, we have to add two
integer numbers and display the result.
class AdditionInt
{
public static
void main (String args[])
{
int a = 6;
int b
= 3;
System.out.println("a
= " + a);
System.out.println("b
=" + b);
int c = a +
b;
System.out.println("Addition
= " + c);
}
}
Output:
a= 6
b= 3
Addition=9
“-” operator in Java:
class SubstractionInt
{
public static
void main (String args[])
{
int a = 6;
int b = 3;
System.out.println("a
= " + a);
System.out.println("b
=" + b);
int c = a -
b;
System.out.println("Subtraction=
" + c);
}
}
Output:
a=6
b=3
Subtraction=3
“*” operator in Java:
Class MultiplicationInt
{
public static
void main (String args[])
{
int a = 6;
int b
= 3;
System.out.println("a
= " + a);
System.out.println("b
=" + b);
int c = a *
b;
System.out.println("Multiplication=
" + c);
}
}
Output:
a=6
b=3
Multiplication=18
“/” operator in Java:
Class DivisionInt
{
public static
void main (String args[])
{
int a = 6;
int b = 3;
System.out.println("a
= " + a);
System.out.println("b
=" + b);
c = a / b;
System.out.println("division="
+ c);
}
}
Output:
a=6
b=3
Division=3
Remainder or modulus operator (%) in
Java:
Class Remainderoptr
{
public static
void main (String args[])
{
int a = 6;
int b
= 3;
System.out.println("a
= " + a);
System.out.println("b
=" + b);
c = a % b;
System.out.println("remainder="
+ c);
}
}
Output:
a=6
b=3
Remainder=0
When
both operands in the expression are integers then the expression is called
Integer expression and the operation is called Integer arithmetic.
When
both operands in the expression are real then the expression is called Real
expression and the operation is called Real
arithmetic.
When one operand in the expression is
integer and other is float then the expression is called Mixed Mode Arithmetic
expression and the operation is called Mixed
Mode Arithmetic operation.
The following program shows the use
of operators with integer data and store data in float variable.
Program: write a program to calculate average of three numbers.
class Avg1
{
public static void main(String
args[])
{
int a=3;
int b=3;
int c=4;
int avg;
avg=a+b+c;
avg=avg/3;
System.out.println(―Avg of three
numbers=‖+avg);
}
}
Output:
Avg of three numbers=3
Logical operators:
When we want to form compound
conditions by combining two or more relations, then we can use logical
operators.
Following table shows the details of
operators.
|
Operators
|
Importance/ significance
|
|
||
|
Logical – OR
|
|
&&
|
Logical –AND
|
|
!
|
Logical –NOT
|
The logical expression defers a value
of true or false. Following table shows the truth table of Logical – OR and
Logical – AND.
Truth table for Logical – OR operator:
|
Operand1
|
Operand3
|
Operand1|| Operand3
|
|
T
|
T
|
T
|
|
T
|
F
|
T
|
|
F
|
T
|
T
|
|
F
|
F
|
F
|
T - True
F - False
Truth table for Logical – AND operator:
|
Operand1
|
Operand3
|
Operand1 && Operand3
|
|
T
|
T
|
T
|
|
T
|
F
|
F
|
|
F
|
T
|
F
|
|
F
|
F
|
F
|
T - True
F – False
Now the following program shows the
use of Logical operators.
class LogicalOptr
{
public static void main (String
args[])
{
boolean a = true;
boolean b = false;
System.out.println("a||b =
" +(a||b));
System.out.println("a&&b
= "+(a&&b));
System.out.println("a!
= "+(!a));
}
}
Output:
a||b = true
a &&b = false
a! = false
Relational Operators:
When evaluation of two numbers is
performed depending upon their relation, assured decisions are made.
The value of relational expression is
either true or false.
If A=7 and A < 10 is true while 10
< A is false.
Following table shows the details of
operators.
|
Operator
|
Importance/ significance
|
|
>
|
Greater than
|
|
<
|
Less than
|
|
!=
|
Not equal to
|
|
>=
|
Greater than or equal to
|
|
<=
|
Less than or equal to
|
Now, following examples show the
actual use of operators.
1) If 10 > 30 then
result is false
2) If 40 > 17 then
result is true
3) If 10 >= 300 then
result is false
4) If 10 <= 10 then result is true
Now the following program shows the
use of operators.
(1) Program 1:
class Reloptr1
{
public static void main (String
args[])
{
int a = 10;
int b = 30;
System.out.println("a>b =
" +(a>b));
System.out.println("a<b =
"+(a<b));
System.out.println("a<=b =
"+(a<=b));
}
}
Output:
a>b = false
a<b = true
a<=b = true
(2) Program 3
class Reloptr3
{
public static void main (String
args[])
{
int a = 10;
int b = 30;
int c = 30;
System.out.println("a>b
= " +(a>b));
System.out.println("a<b
= "+(a<b));
System.out.println("a<=c
= "+(a<=c));
System.out.println("c>b
= " +(c>b));
System.out.println("a<c
= "+(a<c));
System.out.println("b<=c
= "+(b<=c));
}
}
Output:
a>b = false
a<b = true
a<=c = true
c>b = true
a<c = true
b<=c = true
Assignment
Operators:
Assignment Operators
is used to assign the value of an expression to a variable and is also called
as Shorthand operators.
Variable_name
binary_operator = expression
Following table show
the use of assignment operators.
|
Simple Assignment Operator
|
Statement with shorthand Operators
|
|
A=A+1
|
A+=1
|
|
A=A-1
|
A-=1
|
|
A=A/(B+1)
|
A/=(B+1)
|
|
A=A*(B+1)
|
A*=(B+1)
|
|
A=A/C
|
A/=C
|
|
A=A%C
|
A%=C
|
These operators avoid repetition,
easier to read and write.
Now the following program shows the
use of operators.
class Assoptr
{
public static void main (String
args[])
{
int a = 10;
int b = 30;
int c = 30;
a+=1;
b-=3;
c*=7;
System.out.println("a = "
+a);
System.out.println("b =
"+b);
System.out.println("c =
"+c);
}
}
Output:
a = 11
b = 18
c = 310
Conditional Operators:
The character pair ?: is a ternary
operator of Java, which is used to construct conditional expressions of the following
form:
Expression1 ? Expression3 : Expression3
The operator ? : works as follows:
Expression1 is evaluated if it is
true then Expression3 is evaluated and becomes the value of the conditional
expression. If Expression1 is false then Expression3 is evaluated and its value
becomes the conditional expression.
For example:
A=3;
B=4;
C=(A<B)?A:B;
C=(3<4)?3:4;
C=4
Now the following program shows the
use of operators.
class Coptr
{
public static void main (String
args[])
{
int a = 10;
int b = 30;
int c;
c=(a>b)?a:b;
System.out.println("c = "
+c);
c=(a<b)?a:b;
System.out.println("c = "
+c);
}
}
Output:
c = 30
c = 10
program3:Write a program to check whether number is positive or negative.
class PosNeg
{
public static void main(String
args[])
{
int a=10;
int flag=(a<0)?0:1;
if(flag==1)
System.out.println(“Number is
positive”);
else
System.out.println(“Number is
negative”);
}
}
Output:
Number is positive
Increment and Decrement Operators:
The increment operator ++ adds 1 to a
variable. Usually the variable is an integer type, but it can be a floating
point type. The two plus signs must not be split by any character. Usually they
are written immediately next to the variable.
Following table shows the use of
operators.
|
Expression
|
Process
|
Example
|
end result
|
|
A++
|
Add 1 to a variable after use.
|
int A=10,B;
B=A++;
|
A=11
B=10
|
|
++A
|
Add 1 to a variable before use.
|
int A=10,B;
B=++A;
|
A=11
B=11
|
|
A--
|
Subtract 1 from a variable after
use.
|
int A=10,B;
B=A--;
|
A=9
B=10
|
|
--A
|
Subtract 1 from a variable before
use.
|
int A=10,B;
B=--A;
|
A=9
B=9
|
Now the following program shows the
use of operators.
class IncDecOp
{
public static void main(String args[])
{
int x=1;
int y=3;
int u;
int z;
u=++y;
z=x++;
System.out.println(x);
System.out.println(y);
System.out.println(u);
System.out.println(z);
}
}
Output:
3
4
4
1
Bit Wise Operators:
Bit wise operator execute single bit
of their operands.
Following table shows bit wise
operator:
|
Operator
|
Importance/ significance
|
|
|
|
Bitwise OR
|
|
&
|
Bitwise AND
|
|
&=
|
Bitwise AND assignment
|
|
|=
|
Bitwise OR assignment
|
|
^
|
Bitwise Exclusive OR
|
|
<<
|
Left shift
|
|
>>
|
Right shift
|
|
~
|
One‘s complement
|
Now the following program shows the
use of operators.
(1) Program 1
class Boptr1
{
public static void main (String
args[])
{
int a = 4;
int b = a<<3;
System.out.println("a = "
+a);
System.out.println("b = "
+b);
}
}
Output:
a =4
b =16
(2) Program 3
Class Boptr3
{
public static void main (String
args[])
{
int a = 16;
int b = a>>3;
System.out.println("a
= " +a);
System.out.println("b = "
+b);
}
}
Output:
a = 16
b = 3
(Please refer following table)
|
356
|
138
|
64
|
33
|
16
|
8
|
4
|
3
|
1
|
|
38
|
37
|
36
|
35
|
34
|
33
|
33
|
31
|
30
|
Separator:
Separators are symbols. It shows the
separated code.
They describe function of our code.
|
Name
|
use
|
|
()
|
Parameter in method definition,
containing statements for conditions, etc.
|
|
{}
|
It is used for define a code for
method and classes
|
|
[]
|
It is used for declaration of array
|
|
;
|
It is used to show the separate
statement
|
|
,
|
It is used to show the separation
in identifier in variable declaration
|
|
.
|
It is used to show the separate
package name from sub-packages and classes, separate variable and method from
reference variable.
|
Operator Precedence in Java:
An arithmetic expression without any
parentheses will be calculated from left to right using the rules of precedence
of operators.
There are two priority levels of
arithmetic operators are as follows:
(a) High priority (* / %)
(b) Low priority (+ -)
The evaluation process includes two
left to right passes through the expression. During the first pass, the high
priority operators are applied as they are encountered.
During the second pass, the low
priority operators are applied as they are encountered.
For example:
Z=A-B/3+C*3-1
When A=10, B=13, C=3
First pass:
Z=10-(13/3) + (3*3)-1
Z=10-4+3-1
Second pass:
Z=6+3-1
Z=7
Answer is=7
Following table shows associativity
of operators.
|
Operator
|
Associativity
|
Rank
|
|
[ ]
|
Left to right
|
1
|
|
( )
|
Left to right
|
3
|
|
.
|
Left to right
|
|
|
-
|
Right to left
|
|
|
++
|
Right to left
|
|
|
--
|
Right to left
|
|
|
!
|
Right to left
|
|
|
~
|
Right to left
|
|
|
(type)
|
Right to left
|
|
|
*
|
Left to right
|
3
|
|
/
|
Left to right
|
|
|
%
|
Left to right
|
|
|
+
|
Left to right
|
4
|
|
-
|
Left to right
|
|
|
<<
|
Left to right
|
5
|
|
>>
|
Left to right
|
|
|
>>>
|
Left to right
|
|
|
<
|
Left to right
|
6
|
|
<=
|
Left to right
|
|
|
>
|
Left to right
|
|
|
>=
|
Left to right
|
|
|
Instanceof
|
Left to right
|
|
|
==
|
Left to right
|
7
|
|
!=
|
Left to right
|
|
|
&
|
Left to right
|
8
|
|
^
|
Left to right
|
9
|
|
|
|
Left to right
|
10
|
|
&&
|
Left to right
|
11
|
|
||
|
Left to right
|
13
|
|
?:
|
Right to left
|
13
|
|
=
|
Right to left
|
14
|
