5.1.4

Widening Reference Conversions

CONVERSIONS AND PROMOTIONS

Here is a small test program that demonstrates a number of narrowing conver 

sions that lose information:

class Test {

public static void main(String[] args) {

//

A narrowing of

int

 to

short

 loses high bits:

System.out.println("(short)0x12345678==0x" +

Integer.toHexString((short)0x12345678));

//

A

int

 value not fitting in

byte

 changes sign and magnitude:

System.out.println("(byte)255==" + (byte)255);

//

A

float

 value too big to fit gives largest

int

 value:

System.out.println("(int)1e20f==" + (int)1e20f);

//

A NaN converted to

int

 yields zero:

System.out.println("(int)NaN==" + (int)Float.NaN);

//

A

double

 value too large for

float

 yields infinity:

System.out.println("(float) 1e100==" + (float) 1e100);

//

A

double

 value too small for

float

 underflows to zero:

System.out.println("(float)1e 50==" + (float)1e 50);

}

}

This test program produces the following output:

(short)0x12345678==0x5678

(byte)255== 1

(int)1e20f==2147483647

(int)NaN==0

(float) 1e100== Infinity

(float)1e 50==0.0

5.1.4   Widening Reference Conversions

The following conversions are called the

widening reference conversions

:

From any class type

S

 to any class type

T

, provided that

S

 is a subclass of

T

.

(An important special case is that there is a widening conversion to the class

type

Object

 from any other class type.)

From any class type

S

 to any interface type

K

, provided that

S

 implements

K

.

From the null type to any class type, interface type, or array type.

From any interface type

J

 to any interface type

K

, provided that

J

 is a sub 

interface of

K

.

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