1.03 Data Types

In Java every variable and very expression in Java has some type.
Each and every data type is clearly defined.

Each and every assignment should be checked by complier for type-compatibility.

Expression	Java	C Language
`int x = 10.5 ;`
`boolean b = 0 ;`

Object Oriented Analogy

When compared with old languages, Java has Object-Oriented nature
If considered Java alone, Java lacks many OOP features like operator-overloading, multiple-inheritance

Q. Is Java purely object oriented programming language? NO Java is not considered as pure object oriented programming language because several OOPs features are not satisfied by Java. (Like Operator Overloading, Multiple Inheritance). Moreover, we are depending on Primitive Data Types which are non-objects.

Primitive Data Types (8)

Primitive Data Types are further divided into:

Numeric Data Types
1. Integral Data Types
  - byte
  - short
  - int
  - long
2. Floating Point Data Types
  - float
  - double
Non-Numeric Data Types
- char
- boolean

NOTE 01

String is non-primitive because only class can have methods. Primitive can not. And String need many functions to be called upon while processing like substring, indexof, equals, touppercase. It would not have been possible without making it class.
Also class has made it possible to make strings immutable and final to enhance security and efficiency by allowing pooling.
Except boolean and char all other primitive data types are considered as signed data types. because we can represent both positive and negative numbers.

byte

MSB
X	1	1	1	1	1	1	1

size: 8 bits
signed data type
max value: 127
min value: -128
MSB( Most Significant Bit ) acts as signed bit,
- 0 means Non-negative number.
- 1 means negative number.
Positive number will be represented directly in the memory, while negative numbers are represented in the form of 2’s compliments

TEST 01

Q. Which of the following are valid in Java?

Sr. No	Example	Output
1.	byte b = 10;
2.	byte b = 127;
3.	byte b = 128;	Possible loss of Precision: found: int required: byte
4.	byte b = 10.5;	Possible loss of Precision: found: double required: byte
5.	byte b = true;	Incompatible Data Types: found: boolean required: byte
5.	byte b = “nana”;	Incompatible Data Types: found: java.lang.String required: byte

NOTE 02

If you want to handle data in form of strings (files or network etc.) best suitable form is byte because it is supported by both files and network.
Example:

import java.io.FileOutputStream;  
public class FileOutputStreamExample {  
    public static void main(String args[]) {
           try{
             FileOutputStream fout=new FileOutputStream("D:\\testout.txt");
             String s="Welcome to DurgaSoft.";
             byte b[]=s.getBytes();//converting string into byte array
             fout.write(b);        //them writing it to the file via stream
             fout.close();
             System.out.println("success...");
            }
            catch(Exception e) {
              System.out.println(e);
            }
      }
}  

short

Most Rarely used data type in Java
size: 8 bits
signed data type
max value: 2¹⁵-1 : + 32767
min value: -2¹⁵: - 32768
Positive number will be represented directly in the memory, while negative numbers are represented in the form of 2’s compliments

Q. Which of the following are valid in Java?

Sr. No	Example	Output
1.	short s = 32767;
2.	short s = 32768;	Possible loss of Precision: found: int required: short
3.	short s = 10.5;	Possible loss of Precision: found: double required: short
4.	short s = true;	Incompatible Data Types: found: boolean required: short
5.	short s = “nana”;	Incompatible Data Types: found: java.lang.String required: short

Q. When is short data type the best choice?
Java came in 1995, we had 8085, 8086 microprocessors. 16-bit processors were very popular at that time. Data was represented in 16 bit data type.
Hence, as Expected and Provided form are same, read and write operations are more efficient. Hence short is outdated right now as these are not in use.

int

Most commonly used data type in Java
size: 32 bits
signed data type
max value: 2³¹-1 : + 2147483647
min value: -2³¹: - 2147483648

Q. Which of the following are valid in Java?

Sr. No	Example	Output
1.	int x = 2147483647;
2.	int x = 2147483648;	Integer number too large
3.	int x = 2147483648l;	Possible loss of Precision: found: long required: int
4.	int x = true;	Incompatible Data Types: found: boolean required: int

long

size: 8 bytes = 64 bits
signed data type
max value: 2⁶³-1
min value: -2⁶³

Sometimes int range may not be enough to hold big values. In such cases long data type should be used
Example:

Amount of distance travelled by light in 1000 days. long l = 1260006060l;
The number of characters present in a big file may exceed int range. Hence, the return type of length() method is long but not int
long l = file.length();

NOTE 03

All the above data types (byte, short, int, long) meant for representing Integral values. If we want to represent floating point values then we should go for floating point data types.

Floating Point Data Types

There are 2 floating point data points

float : smaller fractional accuracy (5-6 decimal places)
double : smaller fractional accuracy (14-15 decimal places)

float	double
For precision up to 5-6 decimal places	For precision up to 14-15 decimal places
If we want 5 to 6 places of accuracy then we should go for float	If you want 14-15 decimal places of accuracy then we should go for double
Single Precision	Double Precision
float follows single precision	double follows double precision
size: 4 bytes	size: 8 bytes
Range: -3.4e38 to 3.4e38	Range: -1.7e308 to 1.7e308

boolean

Size: IN JAVA SIZE OF boolean NOT APPLICABLE!! (Virtual Machine dependant)
Range: Not Applicable but allowed values are true, false boolean b = true; boolean b = 0;

Sr. No	Example	Output
1.	boolean b = true;
2.	boolean b = 0;	Incompatible Data Types: found: int required: boolean
3.	boolean b = True;	Cannot find symbol: variable:True location: class {className}
2.	boolean b = “True”;	Incompatible Data Types: found: java.lang.String required: boolean

class Test {
    public static void main(String[] args) {
        int x = 0;
        if(x) {
          System.out.println("Hello");
        }
        else {
          System.out.println("Hi");
        }
    }
}

Incompatible Data Types - found: int required: boolean

class Test {
    public static void main(String[] args) {
        while(1) {
          System.out.println("Hi");
        }
    }
}

Incompatible Data Types - found: int required: boolean

char

Old languages (like C, C++) are ASCII code based and number of different ASCII code characters are <= 256.
To represent these 256 characters 8 bits are enough. Hence, the size of char in old languages is 1 byte
But, Java is Unicode based and number of allowed characters are > 256 but <=65536
to represent these many characters 8 bits may not be enough, compulsorily we should go for 16 bit.
Hence, size of char in java is 2 bytes

Old Languages (C,C++) - ASCII Based	Java - Unicode Based
Size: 1 byte	Size: 2 byte
To represent 256 char, 8 bits are enough	8 bits are not enough
`A-Z, a-z, 0-9, symbols`	ASCII + many other characters
Range: 0 - 256	0 - 65535

SUMMARY

Data Type	Size	Range	Wrapper Class	Default Value
byte	1 byte	-2⁷ to 2⁷-1	Byte	0
short	2 bytes	-2¹⁵ to 2¹⁵-1	Short	0
int	4 bytes	-2³¹ to 2³¹-1	Integer	0
long	8 bytes	-2⁶³ to 2⁶³-1	Long	0
float	4 bytes	-3.4e38 to 3.4e38	Float	0.0
double	8 bytes	-1.7e308 to 1.7e308	Double	0.0
boolean	N/A	true, false	Boolean	false
char	4 bytes	0 to 65535	character	0(space)

Note that null cannot be used for primitive data types. null is default value for object data type.

class Test {
    public static void main(String[] args) {
        char ch = null;
    }
}

Incompatible Data Types - found: <nulltype> required: char

1.03 Data Types

Object Oriented Analogy

Primitive Data Types (8)

byte

TEST 01

NOTE 02

short

int

long

NOTE 03

Floating Point Data Types

boolean

char

SUMMARY

Next Topic: 1.04 Literals