Data types

Data types: Every variable has a type, every expression has a type and all types are strictly define moreover every assignment should be checked by the compiler by the type compatibility hence java language is considered as strongly typed language.

Java is pure object-oriented programming or not?

• Java is not considered as pure object-oriented programming language because several oops features (like multiple inheritances, operator overloading) are not supported by java moreover we are depending on primitive data types which are non-objects.

Diagram:

• Except for Boolean and char, all remaining data types are considered assigned data types because we can represent both “+ve” and”-ve” numbers.

Byte:

     Size: 1byte (8bits) Max value: +127 Min value:-128 Range:-128to 127[-27 to 27 -1]

 • The most significant bit acts assign bit. “0” means “+ve” number and “1” means “–ve” number.

 • “+ve” numbers will be represented directly in the memory whereas “–ve” numbers will be represented in 2’s complement form.

Example:

byte b=10;

byte b2=130;//C.E: possible loss of precision

byte b=10.5;//C.E: possible loss of precision

byte b=true;//C.E:incompatible types

byte b="Navneet";//C.E:incompatible types

• a byte data type is best suitable if we are handling data in terms of streams either from the file or from the network.

Short:

• The most rarely used data type in java is short.

Size: 2 bytes

Range: -32768 to 32767(-215 to 215-1)

Example:

short s=130;

short s=32768;//C.E:possible loss of precision

short s=true;//C.E:incompatible types

• The short data type is best suitable for 16-bit processors like 8086 but these processors are completely outdated and hence the corresponding short data type is also out data type.

Int:

• This is the most commonly used data type in java.

 Size: 4 bytes

 Range:-2147483648 to 2147483647 (-231 to 231-1)

Example:

int i=130;

int i=10.5;//C.E:possible loss of precision

int i=true;//C.E:incompatible types

long:

• Whenever int is not enough to hold big values then we should go for a long data type.

Example:

• To hold the no. Of characters present in a big file int may not enough hence the return type of length() method is long.

long l=f.length();//f is a file

 Size: 8 bytes

 Range:-263 to 263-1

Note: All the above data types (byte, short, int and long) can be used to represent whole numbers. If we want to represent real numbers then we should go for floating-point data types.

Floating Point Data types:

float double

1) If we want to 5 to 6 decimal places of

accuracy then we should go for afloat.

1) If we want to 14 to 15 decimal places

of accuracy then we should go for

double.

2) Size:4 bytes. 2) Size:8 bytes.

3) Range:-3.4e38 to 3.4e38. 3) -1.7e308 to1.7e308.

4) float follows a single precision.

4) double follows double-precision

Boolean data type:

Size: Not applicable (virtual machine dependent)

Range: Not applicable but allowed values are true or false.

Which of the following boolean declarations are valid?

Example 1:

              boolean b=true;

              boolean b=True;//C.E:can not find symbol

              boolean b="True";//C.E:incompatible types

              boolean b=0;//C.E:incompatible types

Example 2:

Char data type:

• In java, we are allowed to use any worldwide alphabets character and java is Unicode based to represent all these characters one byte is not enough compulsory we should go for 2 bytes.

Size: 2 bytes

Range: 0 to 65535

Example:

                  char ch1=97;

                  char ch2=65536;//C.E:possible loss of precision

Example:

char ch1=97;

char ch2=65536;//C.E:possible loss of precision

        

• The default value for the object references is “null”.