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:

Notation	Character represented
\n	Newline (0x0a)
\r	Carriage return (0x0d)
\f	Formfeed (0x0c)
\b	Backspace (0x08)
\s	Space (0x20)
\t	tab
\"	Double quote
\'	Single quote
\\	backslash
\ddd	Octal character (ddd)
\uxxxx	Hexadecimal UNICODE character (xxxx)

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:

Java Access Modifiers
Non Access Modifiers

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:
Show Examples

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:
Show Examples

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:
Show Examples

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:
Show Examples

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:
Show Examples

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: