This document discusses Java data types and variables. It begins by defining data types as sets of values with predefined characteristics. It then lists the default Java primitive data types (boolean, char, byte, short, int, long, float, double) along with their default sizes and values. Examples are provided to demonstrate the double and char data types. The document then discusses variables, describing how to declare them and the three types: local, instance, and static variables. It also covers dynamic initialization, default values, and visibility/scope. Finally, the document discusses type conversion and casting between incompatible types in Java.

1. Data types and VariablesData types and Variables
By
Nilesh Dalvi
Lecturer, Patkar-Varde College.Lecturer, Patkar-Varde College.
http://www.slideshare.net/nileshdalvi01
Java and Data StructuresJava and Data Structures

2. Data Types
A data type in a programming language is a set of data
with values having pre-defined characteristics.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

3. Data Types
Data Type Default Value Default size
boolean false 1 bit
char 'u0000‘ or 0 2 byte
byte 0 1 byte
short 0 2 byte
int 0 4 byte
long 0L 8 byte
float 0.0f 4 byte
double 0.0d 8 byte
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

4. Demonstrating double data type
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
class Area
{
public static void main(String args [])
{
double pi, r, a;
r = 10.8; // radius of a circle
pi = 3.146; // value of pi
a = pi*r*r; // compute area
System.out.println("Area of circle" +a);
}
}

5. Demonstrating char data type
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
class CharDemo
{
public static void main(String args [])
{
char ch = 'x';
System.out.println("Character is" +ch);
ch ++; // increment ch;
System.out.println("Character is" +ch);
}
}

6. Variables:
• Declaring variables:
type identifier = value;
• Example:
• Types of variables:
There are three types of variables in java
– local variable
– instance variable
– static variable
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
int a, b, c; // Demonstrating three integers
int d = 3, e, f = 5;
byte z = 22;
double pi = 3.1416;
char x = ‘x’;

7. Variables:
Dynamic initialization:
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
class DynInit {
public static void main(String args []){
double a = 3.0, b = 4.0;
//c is dynamically initialized
double c = Math.sqrt(a*a+b*b);
System.out.println("Hypotenuse is" +c);
}
}

8. Local variable:
• 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.
• 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.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

9. Local variable:
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
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();
}
}

10. Local variable:
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
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();
}
}

11. Instance variable:
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
• 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.
• Created when an object is created with the use of the keyword 'new' and
destroyed when the object is destroyed.
• Instance variables can be declared in class level.
• Access modifiers can be given for instance variables.
• They are visible for all methods, constructors and block in the class.
• Instance variables have default values.
• It can be accessed directly by calling the variable name inside the class.
ObjectReference.VariableName.

12. Instance variable:
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
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("Ram");
empOne.setSalary(1000);
empOne.printEmp();
}
}

13. Class/ Static variable:
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
• 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 created when the program starts and
destroyed when the program stops.
• Visibility is similar to instance variables.
• Default values are same as instance variables.
• Static variables can be accessed by calling with the class name
ClassName.variableName

14. Class/ Static variable:
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
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);
}
}

15. Type Conversion and Casting
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
Java’s Automatic Conversions(Implicit):
• When one type of data is assigned to another type of
variable, an automatic type conversion will take place if the
following conditions satisfied:
– Two types are compatible.
– Destination type is larger than the source type.
– e.g.
int a = byte b;

16. Type Conversion and Casting
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
Casting Incompatible types(Explicit):
• To create a conversion between two incompatible types, you
must use a cast.
• A cast is simply an explicit type conversion.
• It has the general form:
– (target-type) value;
– target-type – specifies the desired type to convert the specified value
to.
– e.g. int a;
byte b;
// ...
b = (byte) a;

17. Demonstrating Casting
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
class Conversion
{
public static void main(String args[])
{
byte b;
int i = 257;
double d = 323.142;
System.out.println("nConversion of int to byte.");
b = (byte) i;
System.out.println("i and b " + i + " " + b);
System.out.println("nConversion of double to int.");
i = (int) d;
System.out.println("d and i " + d + " " + i);
System.out.println("nConversion of double to byte.");
b = (byte) d;
System.out.println("d and b " + d + " " + b);
}
}

18. Demonstrating Casting
(323)10 = (1 0 1 0 0 0 0 1 1 )2
= 0 x 27
+ 1 x 26 + 0 x 25+ 0 x 24+
0 x 23+ 0 x 22+ 1 x 21+ 1 x 20
= (67)10
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
Output:
Conversion of int to byte.
i and b 257 -> 1
Conversion of double to int.
d and i 323.142 -> 323
Conversion of double to byte.
d and b 323.142 -> 67
2 323
2 161 1
2 80 1
2 40 0
2 20 0
2 10 0
2 5 0
2 2 1
2 1 0
2 0 1
Byte is 8-bit

19. Type Conversion and Casting
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
Java type casting is classified in two types:

20. Arrays
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

21. Q & A