Converting Primitives

In Java, we can convert between integer values and floating-point values. Also, since every character corresponds to a number in the Unicode encoding, char types can be converted to and from the integer and floating-point types. boolean is the only primitive datatype that cannot be converted to or from any other primitive datatype.

There are two types of conversions: widening conversion and narrowing conversion.

A widening conversion is when a value of one datatype is converted to a value of another datatype that occupies more bits than the former. There is no issue of data loss in this case.

Correspondingly, A narrowing conversion is when a value of one datatype is converted to a value of another datatype that occupies fewer bits than the former. Data loss can occur in this case.

Java performs widening conversions automatically. But if you want to perform a narrowing conversion (if you are sure that no data loss will occur), then you can force Java to perform the conversion using a language construct known as a cast.

Widening Conversion:

int a = 1;    
double d = a;    // valid conversion to double, no cast needed (widening)

Narrowing Conversion:

double d = 18.96
int b = d;       // invalid conversion to int, will throw a compile-time error
int b = (int) d; // valid conversion to int, but result is truncated (gets rounded down)
                 // This is type-casting
                 // Now, b = 18