CONVERSIONS AND PROMOTIONS

Conversions and Promotions

5

Casting conversion ( 5.4) converts the type of an expression to a type explic 

itly specified by a cast operator ( 15.15). It is more inclusive than assignment

or method invocation conversion, allowing any specific conversion other than

a string conversion, but certain casts to a reference type may cause an excep 

tion at run time.

String conversion ( 5.4,  15.17.1) allows any type to be converted to type

String

.

Numeric promotion ( 5.6) brings the operands of a numeric operator to a

common type so that an operation can be performed.

Here are some examples of the various contexts for conversion:

class Test {

public static void main(String[] args) {

//

Casting conversion ( 5.4) of a

float

 literal to

//

type

int

. Without the cast operator, this would

//

be a compile time error, because this is a

//

narrowing conversion ( 5.1.3):

int i = (int)12.5f;

//

String conversion ( 5.4) of

i

's

int

 value:

System.out.println("(int)12.5f==" + i);

//

Assignment conversion ( 5.2) of

i

's value to type

// float

. This is a widening conversion ( 5.1.2):

float f = i;

//

String conversion of

f

 s

float

 value:

System.out.println("after float widening: " + f);

//

Numeric promotion ( 5.6) of

i

's value to type

// float

. This is a binary numeric promotion.

//

After promotion, the operation is

float*float

:

System.out.print(f);

f = f * i;

//

Two string conversions of

i

 and

f

:

System.out.println("*" + i + "==" + f);

//

Method invocation conversion ( 5.3) of

f

's value

//

to type

double

, needed because the method

Math.sin

//

accepts only a

double

 argument:

double d = Math.sin(f);

//

Two string conversions of

f

 and

d

:

System.out.println("Math.sin(" + f + ")==" + d);

}

}

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