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Variables and Datatypes in Java

Variables in Java

  • A variable is a name given to the memory location.
  • A variable is used to store value.
  • We can change the value of the variable when needed.
  • Every variable in the java program must be declared before it is used.
  • To create every variable(declare) we use datatype.

Datatypes in Java

  • The data types are keywords that are used to declare the variables.
  • The datatype decides the type of value that can be stored in the variable.
  • The datatype decides what is the size of the memory location which is used as variable/ by variable.
  • The datatype also decides the range of the values that can be stored in the variable.
  • The syntax for creating variables is as follows:
datatype variable_name=value;

The following table shows all 8 primary datatypes available in java:

DatatypeType of valueSizeRange
byteInteger1 byte-128 to 127
shortInteger2 byte-32768 to 32767
intInteger4 byte-2147483648 to 2147483648
longInteger8 byte-263 to 263-1
floatReal4 byte32-bit IEEE 754
doubleReal8 byte64-bit IEEE 754
booleanBoolean (true/false)1 bittrue,false
charCharacter2 byte0 to 65535

The following example creates a variable of int type and stores 100 into it.

int a=100;

In java, if you try to store a value beyond the permitted range of datatype then it's a syntax error.

The following declaration gives a syntax error.

byte b=130;

If you try to assign the value of a larger type in a variable of a smaller data type then it is a syntax error because it may lead to a loss in the data:

For example:

short s=123456;

The above statement generates an error because the range of short is -32768 to 32767, and we are trying to assign 123456 into the short variable which results in the loss of the data.

Similarly, if you assign a double value to a float variable it will lead to a syntax error (possible lossy conversion from double to float):

float radius=3.14;

Remember that any real literal by default treated as double, it means 3.14 is a double value.

If you want to make a real literal as float, then you must use the letter f or letter F after the real value, it means that 3.14f or 3.14F is a float value, so writing the above radius declaration will work:

float rad=3.14f;

Consider the below example:

double x=2.12;

int p=x; This will also generate an error because we are trying to assign a double value into the int variable which leads to possible lossy conversion.

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