CONVERSIONS AND PROMOTIONS

Assignment Conversion

5.2

class Test {

public static void main(String[] args) {

//

Assignments to variables of class type:

Point p = new Point();

p = new Point3D();

//

ok: because

Point3d

 is a

//

subclass of

Point

Point3D p3d = p;

//

error: will require a cast because a

// Point

 might not be a

Point3D

//

(even though it is, dynamically,

//

in this example.)

//

Assignments to variables of type

Object

:

Object o = p;

//

ok: any object to

Object

int[] a = new int[3];

Object o2 = a;

//

ok: an array to

Object

//

Assignments to variables of interface type:

ColoredPoint cp = new ColoredPoint();

Colorable c = cp;

//

ok:

ColoredPoint

 implements

// Colorable

//

Assignments to variables of array type:

byte[] b = new byte[4];

a = b;

//

error: these are not arrays

//

of the same primitive type

Point3D[] p3da = new Point3D[3];

Point[] pa = p3da;

//

ok: since we can assign a

// Point3D

 to a

Point

p3da = pa;

//

error: (cast needed) since a

Point

//

can t be assigned to a

Point3D

}

}

Assignment of a value of compile time reference type

S

 (source) to a variable

of compile time reference type

T

 (target) is checked as follows:

If

S

 is a class type:

N

If

T

 is a class type, then

S

 must either be the same class as

T

, or

S

 must be a

subclass of

T

, or a compile time error occurs.

N

If

T

 is an interface type, then

S

 must implement interface

T

, or a compile 

time error occurs.

N

If

T

 is an array type, then a compile time error occurs.

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