Java Basic Data Types
Variables are nothing but
reserved memory locations to store values. This means that when you create a
variable you reserve some space in memory.
Based on the data type of a
variable, the operating system allocates memory and decides what can be stored
in the reserved memory. Therefore, by assigning different data types to
variables, you can store integers, decimals, or characters in these variables.
There are two data types
available in Java:
·
Primitive Data Types
·
Reference/Object Data Types
Primitive
Data Types:
There are eight primitive
data types supported by Java. Primitive data types are predefined by the
language and named by a key word. Let us now look into detail about the eight
primitive data types.
byte:
·
Byte data type is a 8-bit signed two's complement integer.
·
Minimum value is -128 (-2^7)
·
Maximum value is 127 (inclusive)(2^7 -1)
·
Default value is 0
·
Byte data type is used to save space in large arrays, mainly in
place of integers, since a byte is four times smaller than an int.
·
Example : byte a = 100 , byte b = -50
short:
·
Short data type is a 16-bit signed two's complement integer.
·
Minimum value is -32,768 (-2^15)
·
Maximum value is 32,767(inclusive) (2^15 -1)
·
Short data type can also be used to save memory as byte data type.
A short is 2 times smaller than an int
·
Default value is 0.
·
Example : short s= 10000 , short r = -20000
int:
·
Int data type is a 32-bit signed two's complement integer.
·
Minimum value is - 2,147,483,648.(-2^31)
·
Maximum value is 2,147,483,647(inclusive).(2^31 -1)
·
Int is generally used as the default data type for integral values
unless there is a concern about memory.
·
The default value is 0.
·
Example : int a = 100000, int b = -200000
long:
·
Long data type is a 64-bit signed two's complement integer.
·
Minimum value is -9,223,372,036,854,775,808.(-2^63)
·
Maximum value is 9,223,372,036,854,775,807 (inclusive). (2^63 -1)
·
This type is used when a wider range than int is needed.
·
Default value is 0L.
·
Example : long a = 100000L, int b = -200000L
float:
·
Float data type is a single-precision 32-bit IEEE 754 floating
point.
·
Float is mainly used to save memory in large arrays of floating
point numbers.
·
Default value is 0.0f.
·
Float data type is never used for precise values such as currency.
·
Example : float f1 = 234.5f
double:
·
double data type is a double-precision 64-bit IEEE 754 floating
point.
·
This data type is generally used as the default data type for
decimal values. generally the default choice.
·
Double data type should never be used for precise values such as
currency.
·
Default value is 0.0d.
·
Example : double d1 = 123.4
boolean:
·
boolean data type represents one bit of information.
·
There are only two possible values : true and false.
·
This data type is used for simple flags that track true/false
conditions.
·
Default value is false.
·
Example : boolean one = true
char:
·
char data type is a single 16-bit Unicode character.
·
Minimum value is '\u0000' (or 0).
·
Maximum value is '\uffff' (or 65,535 inclusive).
·
Char data type is used to store any character.
·
Example . char letterA ='A'
Reference
Data Types:
·
Reference variables are created using defined constructors of the
classes. They are used to access objects. These variables are declared to be of
a specific type that cannot be changed. For example, Employee, Puppy etc.
·
Class objects, and various type of array variables come under
reference data type.
·
Default value of any reference variable is null.
·
A reference variable can be used to refer to any object of the
declared type or any compatible type.
·
Example : Animal animal = new Animal("giraffe");
Java
Literals:
A literal is a source code
representation of a fixed value. They are represented directly in the code
without any computation.
Literals can be assigned to
any primitive type variable. For example:
byte a = 68;
char a = 'A'
byte, int, long, and short
can be expressed in decimal(base 10),hexadecimal(base 16) or octal(base 8)
number systems as well.
Prefix 0 is used to indicates
octal and prefix 0x indicates hexadecimal when using these number systems for
literals. For example:
int decimal = 100;
int octal = 0144;
int hexa = 0x64;
String literals in Java are
specified like they are in most other languages by enclosing a sequence of
characters between a pair of double quotes. Examples of string literals are:
"Hello World"
"two\nlines"
"\"This is in quotes\""
String and char types of
literals can contain any Unicode characters. For example:
char a = '\u0001';
String a = "\u0001";
Java language supports few
special escape sequences for String and char literals as well. They are:
Java Variable Types
In Java, all variables must
be declared before they can be used. The basic form of a variable declaration
is shown here:
type identifier [ = value][, identifier [= value] ...] ;
The type is one of Java's datatypes. The identifier is the name of the variable. To
declare more than one variable of the specified type, use a comma-separated
list.
Here are several examples of
variable declarations of various types. Note that some include an
initialization.
int a, b, c; // declares three ints, a, b, and c.
int d = 3, e, f = 5; // declares three more ints, initializing
// d and f.
byte z = 22; // initializes z.
double pi = 3.14159; // declares an approximation of pi.
char x = 'x'; // the variable x has the value 'x'.
This chapter will explain
various variable types available in Java Language. There are three kinds of
variables in Java:
·
Local variables
·
Instance variables
·
Class/static variables
Local
variables :
·
Local variables are declared in methods, constructors, or blocks.
·
Local variables are created when the method, constructor or block
is entered and the variable will be destroyed once it exits the method,
constructor or block.
·
Access modifiers cannot be used for local variables.
·
Local variables are visible only within the declared method,
constructor or block.
·
Local variables are implemented at stack level internally.
·
There is no default value for local variables so local variables
should be declared and an initial value should be assigned before the first
use.
Example:
Here age is a local variable. This is defined
inside pupAge() method and its scope is limited to
this method only.
public class Test{
public void pupAge(){
int age = 0;
age = age + 7;
System.out.println("Puppy age is : " + age);
}
public static void main(String args[]){
Test test = new Test();
test.pupAge();
}
}
This would produce following
result:
Puppy age is: 7
Example:
Following
example uses age without initializing it, so it would give
an error at the time of compilation.
public class Test{
public void pupAge(){
int age;
age = age + 7;
System.out.println("Puppy age is : " + age);
}
public static void main(String args[]){
Test test = new Test();
test.pupAge();
}
}
This would produce following
error while compiling it:
Test.java:4:variable number might not have been initialized
age = age + 7;
^
1 error
Instance
variables :
·
Instance variables are declared in a class, but outside a method,
constructor or any block.
·
When a space is allocated for an object in the heap a slot for
each instance variable value is created.
·
Instance variables are created when an object is created with the
use of the key word 'new' and destroyed when the object is destroyed.
·
Instance variables hold values that must be referenced by more
than one method, constructor or block, or essential parts of an object.s state
that must be present through out the class.
·
Instance variables can be declared in class level before or after
use.
·
Access modifiers can be given for instance variables.
·
The instance variables are visible for all methods, constructors
and block in the class. Normally it is recommended to make these variables
private (access level).However visibility for subclasses can be given for these
variables with the use of access modifiers.
·
Instance variables have default values. For numbers the default
value is 0, for Booleans it is false and for object references it is null.
Values can be assigned during the declaration or within the constructor.
·
Instance variables can be accessed directly by calling the
variable name inside the class. However within static methods and different
class ( when instance variables are given accessibility) the should be called
using the fully qualified name .ObjectReference.VariableName.
Example:
import java.io.*;
public class Employee{
// this instance variable is visible for any child class.
public String name;
// salary variable is visible in Employee class only.
private double salary;
// The name variable is assigned in the constructor.
public Employee (String empName){
name = empName;
}
// The salary variable is assigned a value.
public void setSalary(double empSal){
salary = empSal;
}
// This method prints the employee details.
public void printEmp(){
System.out.println("name : " + name );
System.out.println("salary :" + salary);
}
public static void main(String args[]){
Employee empOne = new Employee("Ransika");
empOne.setSalary(1000);
empOne.printEmp();
}
}
This would produce following
result:
name : Ransika
salary :1000.0
Class/static
variables :
·
Class variables also known as static variables are declared with
the static keyword in a class, but outside a
method, constructor or a block.
·
There would only be one copy of each class variable per class,
regardless of how many objects are created from it.
·
Static variables are rarely used other than being declared as constants.
Constants are variables that are declared as public/private, final and static.
Constant variables never change from their initial value.
·
Static variables are stored in static memory. It is rare to use
static variables other than declared final and used as either public or private
constants.
·
Static variables are created when the program starts and destroyed
when the program stops.
·
Visibility is similar to instance variables. However, most static
variables are declared public since they must be available for users of the
class.
·
Default values are same as instance variables. For numbers the
default value is 0, for Booleans it is false and for object references it is
null. Values can be assigned during the declaration or within the constructor.
Additionally values can be assigned in special static initializer blocks.
·
Static variables can be accessed by calling with the class name . ClassName.VariableName.
·
When declaring class variables as public static final, then
variables names (constants) are all in upper case. If the static variables are
not public and final the naming syntax is the same as instance and local
variables.
Example:
import java.io.*;
public class Employee{
// salary variable is a private static variable
private static double salary;
// DEPARTMENT is a constant
public static final String DEPARTMENT = "Development ";
public static void main(String args[]){
salary = 1000;
System.out.println(DEPARTMENT+"average salary:"+salary);
}
}
This would produce following
result:
Development average salary:1000
Note: If the variables are access from an outside class the constant
should be accessed as Employee.DEPARTMENT
Java Modifier Types
Modifiers are keywords that
you add to those definitions to change their meanings. The Java language has a
wide variety of modifiers, including the following:
To use a modifier, you
include its keyword in the definition of a class, method, or variable. The
modifier precedes the rest of the statement, as in the following examples
(Italic ones):
public class className {
// ...
}
private boolean myFlag;
static final double weeks = 9.5;
protected static final int BOXWIDTH = 42;
public static void main(String[] arguments) {
// body of method
}
Access
Control Modifiers:
Java provides a number of
access modifiers to set access levels for classes, variables, methods and
constructors. The four access levels are:
·
Visible to the package. the default. No modifiers are needed.
·
Visible to the class only (private).
·
Visible to the world (public).
·
Visible to the package and all subclasses (protected).
Non Access
Modifiers:
Java provides a number of
non-access modifiers to achieve many other functionality.
·
The static modifier for creating class methods
and variables
·
The final modifier for finalizing the
implementations of classes, methods, and variables.
·
The abstract modifier for creating abstract classes
and methods.
·
The synchronized and volatile modifiers, which are used for threads.
Java Basic Operators
Java provides a rich set of
operators to manipulate variables. We can divide all the Java operators into
the following groups:
·
Arithmetic Operators
·
Relational Operators
·
Bitwise Operators
·
Logical Operators
·
Assignment Operators
·
Misc Operators
The
Arithmetic Operators:
Arithmetic operators are used
in mathematical expressions in the same way that they are used in algebra. The
following table lists the arithmetic operators:
Assume integer variable A
holds 10 and variable B holds 20 then:
|
Operator
|
Description
|
Example
|
|
+
|
Addition - Adds values on either side
of the operator
|
A + B will give 30
|
|
-
|
Subtraction - Subtracts right hand
operand from left hand operand
|
A - B will give -10
|
|
*
|
Multiplication - Multiplies values on
either side of the operator
|
A * B will give 200
|
|
/
|
Division - Divides left hand operand by
right hand operand
|
B / A will give 2
|
|
%
|
Modulus - Divides left hand operand by
right hand operand and returns remainder
|
B % A will give 0
|
|
++
|
Increment - Increase the value of
operand by 1
|
B++ gives 21
|
|
--
|
Decrement - Decrease the value of
operand by 1
|
B-- gives 19
|
The
Relational Operators:
There are following
relational operators supported by Java language
Assume variable A holds 10
and variable B holds 20 then:
|
Operator
|
Description
|
Example
|
|
==
|
Checks if the value of two operands are
equal or not, if yes then condition becomes true.
|
(A == B) is not true.
|
|
!=
|
Checks if the value of two operands are
equal or not, if values are not equal then condition becomes true.
|
(A != B) is true.
|
|
>
|
Checks if the value of left operand is
greater than the value of right operand, if yes then condition becomes true.
|
(A > B) is not true.
|
|
<
|
Checks if the value of left operand is
less than the value of right operand, if yes then condition becomes true.
|
(A < B) is true.
|
|
>=
|
Checks if the value of left operand is
greater than or equal to the value of right operand, if yes then condition
becomes true.
|
(A >= B) is not true.
|
|
<=
|
Checks if the value of left operand is
less than or equal to the value of right operand, if yes then condition
becomes true.
|
(A <= B) is true.
|
The
Bitwise Operators:
Java defines several bitwise
operators which can be applied to the integer types, long, int, short, char,
and byte.
Bitwise operator works on
bits and perform bit by bit operation. Assume if a = 60; and b = 13; Now in
binary format they will be as follows:
a = 0011 1100
b = 0000 1101
-----------------
a&b = 0000 1100
a|b = 0011 1101
a^b = 0011 0001
~a = 1100 0011
The following table lists the
bitwise operators:
Assume integer variable A
holds 60 and variable B holds 13 then:
|
Operator
|
Description
|
Example
|
|
&
|
Binary AND Operator copies a bit to the
result if it exists in both operands.
|
(A & B) will give 12 which is 0000
1100
|
|
|
|
Binary OR Operator copies a bit if it
exists in eather operand.
|
(A | B) will give 61 which is 0011 1101
|
|
^
|
Binary XOR Operator copies the bit if
it is set in one operand but not both.
|
(A ^ B) will give 49 which is 0011 0001
|
|
~
|
Binary Ones Complement Operator is
unary and has the efect of 'flipping' bits.
|
(~A ) will give -60 which is 1100 0011
|
|
<<
|
Binary Left Shift Operator. The left
operands value is moved left by the number of bits specified by the right
operand.
|
A << 2 will give 240 which is
1111 0000
|
|
>>
|
Binary Right Shift Operator. The left
operands value is moved right by the number of bits specified by the right
operand.
|
A >> 2 will give 15 which is 1111
|
|
>>>
|
Shift right zero fill operator. The
left operands value is moved right by the number of bits specified by the
right operand and shifted values are filled up with zeros.
|
A >>>2 will give 15 which is
0000 1111
|
The
Logical Operators:
The following table lists the
logical operators:
Assume boolean variables A
holds true and variable B holds false then:
|
Operator
|
Description
|
Example
|
|
&&
|
Called Logical AND operator. If both
the operands are non zero then then condition becomes true.
|
(A && B) is false.
|
|
||
|
Called Logical OR Operator. If any of
the two operands are non zero then then condition becomes true.
|
(A || B) is true.
|
|
!
|
Called Logical NOT Operator. Use to
reverses the logical state of its operand. If a condition is true then
Logical NOT operator will make false.
|
!(A && B) is true.
|
The
Assignment Operators:
There are following
assignment operators supported by Java language:
|
Operator
|
Description
|
Example
|
|
=
|
Simple assignment operator, Assigns
values from right side operands to left side operand
|
C = A + B will assigne value of A + B
into C
|
|
+=
|
Add AND assignment operator, It adds
right operand to the left operand and assign the result to left operand
|
C += A is equivalent to C = C + A
|
|
-=
|
Subtract AND assignment operator, It
subtracts right operand from the left operand and assign the result to left
operand
|
C -= A is equivalent to C = C - A
|
|
*=
|
Multiply AND assignment operator, It
multiplies right operand with the left operand and assign the result to left
operand
|
C *= A is equivalent to C = C * A
|
|
/=
|
Divide AND assignment operator, It
divides left operand with the right operand and assign the result to left
operand
|
C /= A is equivalent to C = C / A
|
|
%=
|
Modulus AND assignment operator, It
takes modulus using two operands and assign the result to left operand
|
C %= A is equivalent to C = C % A
|
|
<<=
|
Left shift AND assignment operator
|
C <<= 2 is same as C = C <<
2
|
|
>>=
|
Right shift AND assignment operator
|
C >>= 2 is same as C = C >>
2
|
|
&=
|
Bitwise AND assignment operator
|
C &= 2 is same as C = C & 2
|
|
^=
|
bitwise exclusive OR and assignment
operator
|
C ^= 2 is same as C = C ^ 2
|
|
|=
|
bitwise inclusive OR and assignment
operator
|
C |= 2 is same as C = C | 2
|
Misc
Operators
There are few other operators
supported by Java Language.
Conditional
Operator ( ? : ):
Conditional operator is also
known as the ternary operator. This operator consists of three operands and is
used to evaluate boolean expressions. The goal of the operator is to decide
which value should be assigned to the variable. The operator is written as :
variable x = (expression) ? value if true : value if false
Following is the example:
public class Test {
public static void main(String args[]){
int a , b;
a = 10;
b = (a == 1) ? 20: 30;
System.out.println( "Value of b is : " + b );
b = (a == 10) ? 20: 30;
System.out.println( "Value of b is : " + b );
}
}
This would produce following
result:
Value of b is : 30
Value of b is : 20
instanceOf
Operator:
This operator is used only
for object reference variables. The operator checks whether the object is of a
particular type(class type or interface type). instanceOf operator is wriiten
as:
( Object reference variable ) instanceOf (class/interface type)
If the object referred by the
variable on the left side of the operator passes the IS-A check for the
class/interface type on the right side then the result will be true. Following
is the example:
String name = = 'James';
boolean result = name instanceOf String;
// This will return true since name is type of String
This operator will still
return true if the object being compared is the assignment compatible with the
type on the right. Following is one more example:
class Vehicle {}
public class Car extends Vehicle {
public static void main(String args[]){
Vehicle a = new Car();
boolean result = a instanceof Car;
System.out.println( result);
}
}
This would produce following
result:
true
Precedence
of Java Operators:
Operator precedence
determines the grouping of terms in an expression. This affects how an
expression is evaluated. Certain operators have higher precedence than others;
for example, the multiplication operator has higher precedence than the
addition operator:
For example x = 7 + 3 * 2;
Here x is assigned 13, not 20 because operator * has higher precedenace than +
so it first get multiplied with 3*2 and then adds into 7.
Here operators with the
highest precedence appear at the top of the table, those with the lowest appear
at the bottom. Within an expression, higher precedenace operators will be
evaluated first.
|
Category
|
Operator
|
Associativity
|
|
Postfix
|
() [] . (dot operator)
|
Left to right
|
|
Unary
|
++ - - ! ~
|
Right to left
|
|
Multiplicative
|
* / %
|
Left to right
|
|
Additive
|
+ -
|
Left to right
|
|
Shift
|
>> >>> <<
|
Left to right
|
|
Relational
|
> >= < <=
|
Left to right
|
|
Equality
|
== !=
|
Left to right
|
|
Bitwise AND
|
&
|
Left to right
|
|
Bitwise XOR
|
^
|
Left to right
|
|
Bitwise OR
|
|
|
Left to right
|
|
Logical AND
|
&&
|
Left to right
|
|
Logical OR
|
||
|
Left to right
|
|
Conditional
|
?:
|
Right to left
|
|
Assignment
|
= += -= *= /= %= >>= <<=
&= ^= |=
|
Right to left
|
|
Comma
|
,
|
Left to right
|
Java Loops - for,
while and do...while
There may be a sitution when
we need to execute a block of code several number of times, and is often
referred to as a loop.
Java has very flexible three
looping mechanisms. You can use one of the following three loops:
·
while Loop
·
do...while Loop
·
for Loop
As of java
5 the enhanced
for loop was
introduced. This is mainly used for Arrays.
The while
Loop:
A while loop is a control
structure that allows you to repeat a task a certain number of times.
Syntax:
The syntax of a while loop
is:
while(Boolean_expression)
{
//Statements
}
When
executing, if the boolean_expression result is true then the actions inside the loop will be executed.
This will continue as long as the expression result is true.
Here
key point of the while loop is that the loop might not ever run. When the expression is
tested and the result is false, the loop body will be skipped and the first
statement after the while loop will be executed.
Example:
public class Test {
public static void main(String args[]) {
int x = 10;
while( x < 20 ) {
System.out.print("value of x : " + x );
x++;
System.out.print("\n");
}
}
}
This would produce following
result:
value of x : 10
value of x : 11
value of x : 12
value of x : 13
value of x : 14
value of x : 15
value of x : 16
value of x : 17
value of x : 18
value of x : 19
The
do...while Loop:
A do...while loop is similar
to a while loop, except that a do...while loop is guaranteed to execute at
least one time.
Syntax:
The syntax of a do...while
loop is:
do
{
//Statements
}while(Boolean_expression);
Notice that the Boolean
expression appears at the end of the loop, so the statements in the loop
execute once before the Boolean is tested.
If the Boolean expression is
true, the flow of control jumps back up to do, and the statements in the loop
execute again. This process repeats until the Boolean expression is false.
Example:
public class Test {
public static void main(String args[]){
int x = 10;
do{
System.out.print("value of x : " + x );
x++;
System.out.print("\n");
}while( x < 20 );
}
}
This would produce following
result:
value of x : 10
value of x : 11
value of x : 12
value of x : 13
value of x : 14
value of x : 15
value of x : 16
value of x : 17
value of x : 18
value of x : 19
The for
Loop:
A for loop is a repetition
control structure that allows you to efficiently write a loop that needs to
execute a specific number of times.
A for loop is useful when you
know how many times a task is to be repeated.
Syntax:
The syntax of a for loop is:
for(initialization; Boolean_expression; update)
{
//Statements
}
Here is the flow of control
in a for loop:
·
The initialization step is executed first, and only once. This
step allows you to declare and initialize any loop control variables. You are
not required to put a statement here, as long as a semicolon appears.
·
Next, the Boolean expression is evaluated. If it is true, the body
of the loop is executed. If it is false, the body of the loop does not execute
and flow of control jumps to the next statement past the for loop.
·
After the body of the for loop executes, the flow of control jumps
back up to the update statement. This statement allows you to update any loop
control variables. This statement can be left blank, as long as a semicolon
appears after the Boolean expression.
·
The Boolean expression is now evaluated again. If it is true, the
loop executes and the process repeats itself (body of loop, then update
step,then Boolean expression). After the Boolean expression is false, the for
loop terminates.
Example:
public class Test {
public static void main(String args[]) {
for(int x = 10; x < 20; x = x+1) {
System.out.print("value of x : " + x );
System.out.print("\n");
}
}
}
This would produce following
result:
value of x : 10
value of x : 11
value of x : 12
value of x : 13
value of x : 14
value of x : 15
value of x : 16
value of x : 17
value of x : 18
value of x : 19
Enhanced
for loop in Java:
As of java 5 the enhanced for
loop was introduced. This is mainly used for Arrays.
Syntax:
The syntax of enhanced for
loop is:
for(declaration : expression)
{
//Statements
}
·
Declaration . The newly declared block variable, which is of a type compatible
with the elements of the array you are accessing. The variable will be
available within the for block and its value would be the same as the current
array element.
·
Expression . This evaluate to the array you need to loop through. The
expression can be an array variable or method call that returns an array.
Example:
public class Test {
public static void main(String args[]){
int [] numbers = {10, 20, 30, 40, 50};
for(int x : numbers ){
System.out.print( x );
System.out.print(",");
}
System.out.print("\n");
String [] names ={"James", "Larry", "Tom", "Lacy"};
for( String name : names ) {
System.out.print( name );
System.out.print(",");
}
}
}
This would produce following
result:
10,20,30,40,50,
James,Larry,Tom,Lacy,
The break
Keyword:
The break keyword is used to stop the entire loop. The break keyword must be
used inside any loop or a switch statement.
The break keyword will stop
the execution of the innermost loop and start executing the next line of code
after the block.
Syntax:
The syntax of a break is a
single statement inside any loop:
break;
Example:
public class Test {
public static void main(String args[]) {
int [] numbers = {10, 20, 30, 40, 50};
for(int x : numbers ) {
if( x == 30 ) {
break;
}
System.out.print( x );
System.out.print("\n");
}
}
}
This would produce following
result:
10
20
The
continue Keyword:
The continue keyword can be used in any of the loop control structures. It
causes the loop to immediately jump to the next iteration of the loop.
·
In a for loop, the continue keyword causes flow of control to
immediately jump to the update statement.
·
In a while loop or do/while loop, flow of control immediately
jumps to the Boolean expression.
Syntax:
The syntax of a continue is a
single statement inside any loop:
continue;
Example:
public class Test {
public static void main(String args[]) {
int [] numbers = {10, 20, 30, 40, 50};
for(int x : numbers ) {
if( x == 30 ) {
continue;
}
System.out.print( x );
System.out.print("\n");
}
}
}
This would produce following
result:
10
20
40
50
Java - Numbers Class
Normally, when we work with
Numbers, we use primitive data types such as byte, int, long, double etc.
Example:
int i = 5000;
float gpa = 13.65;
byte mask = 0xaf;
However in development we
come across situations were we need to use objects instead of primitive data
types. In-order to achieve this Java provides wrapper classes for each
primitive data type.
All the wrapper classes (
Integer, Long, Byte, Double, Float, Short) are subclasses of the abstract class
Number.
This
wrapping is taken care of by the compiler The process is called boxing. So when
a primitive is used when an object is required the compiler boxes the primitive
type in its wrapper class. Similarly the compiler unboxes the object to a
primitive as well. The Number is part of the java.lang package.
Here is an example of boxing
and unboxing:
public class Test{
public static void main(String args[]){
Integer x = 5; // boxes int to an Integer object
x = x + 10; // unboxes the Integer to a int
System.out.println(x);
}
}
This would produce following
result:
15
When x is assigned integer
values, the compiler boxes the integer because x is integer objects. Later, x
is unboxed so that they can be added as integers.
Number
Methods:
Here is the list of the
instance methods that all the subclasses of the Number class implement:
|
SN
|
Methods with Description
|
|
1
|
xxxValue()
Converts the value of this Number object to the xxx data type and returned it. |
|
2
|
compareTo()
Compares this Number object to the argument. |
|
3
|
equals()
Determines whether this number object is equal to the argument. |
|
4
|
valueOf()
Returns an Integer object holding the value of the specified primitive. |
|
5
|
toString()
Returns a String object representing the value of specified int or Integer. |
|
6
|
parseInt()
This method is used to get the primitive data type of a certain String. |
|
7
|
abs()
Returns the absolute value of the argument. |
|
8
|
ceil()
Returns the smallest integer that is greater than or equal to the argument. Returned as a double. |
|
9
|
floor()
Returns the largest integer that is less than or equal to the argument. Returned as a double. |
|
10
|
rint()
Returns the integer that is closest in value to the argument. Returned as a double. |
|
11
|
round()
Returns the closest long or int, as indicated by the method's return type, to the argument. |
|
12
|
min()
Returns the smaller of the two arguments. |
|
13
|
max()
Returns the larger of the two arguments. |
|
14
|
exp()
Returns the base of the natural logarithms, e, to the power of the argument. |
|
15
|
log()
Returns the natural logarithm of the argument. |
|
16
|
pow()
Returns the value of the first argument raised to the power of the second argument. |
|
17
|
sqrt()
Returns the square root of the argument. |
|
18
|
sin()
Returns the sine of the specified double value. |
|
19
|
cos()
Returns the cosine of the specified double value. |
|
20
|
tan()
Returns the tangent of the specified double value. |
|
21
|
asin()
Returns the arcsine of the specified double value. |
|
22
|
acos()
Returns the arccosine of the specified double value. |
|
23
|
atan()
Returns the arctangent of the specified double value. |
|
24
|
atan2()
Converts rectangular coordinates (x, y) to polar coordinate (r, theta) and returns theta. |
|
25
|
toDegrees()
Converts the argument to degrees |
|
26
|
toRadians()
Converts the argument to radians. |
|
27
|
random()
Returns a random number. |
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