Object type casting

Type Casting

 Converting an object of one class to an
object of another class is possible if the
object types are compatible.
 Java will perform some conversion
automatically. Such conversions are
known as implicit type casting.
 Conversions forced by the programmer is
known as explicit type casting.

Eg.,

PERSON
X

Y Z TEACHER STUDENT

Z1 Z2

UG_STUD PG_STUD
ENT ENT

Class definition

public Class X Class Y extends X {
{
public void F(); public void F();
public void F1(); public void F2a();
} }
// X is a super class of Y Class Z extends X
and Z which are sub {
classes. public void F();
public void F2b();
}

Cont.,

Class Z1 extends Z
{
public void F();
public void F3a();
} // Z1,Z2 are subclasses which is
derived from Z.
Class Z2 extends Z
{
public void F();
public void F3b();
}

Cont..

1. X x = new X(); //no casting required
2. Y y = new Y(); //no casting required
3. Z z = new Z(); //no casting required
4. X xy = new Y(); // compiles ok (up the
hierarchy)
5. X xz = new Z(); // compiles ok (up the
hierarchy)
6. Y yz = new Z();// incompatible type
(siblings)

Cont..

1. Y yz = new Z(); //incompatible type
(siblings)
2. Y y1 = new X(); //incompatible. X is not a
Y
3. Z z1 = new X(); //X is not a Z
4. X x1 = y; // compiles ok (y is subclass of X)
5. X x2 = z; // compiles ok (z is subclass of X)

Object type Casting

Y yx = (Y) x1; // compiles and runs ok (x1 is type Y)
Z zx = (Z) x2; // compiles and runs ok (x2 is type Z)
// X xy = new Y(); (declared earlier)
xy.F(); //calls method F() of class X
((Y)xy).F(); //explicitly type cast xy to
method call F() class Y
((Y)xy).F2a(); // call the method F2a()
from class Y

Object Type Casting.,

X xz1=new Z1();

((Z1)xz1).F();//calls method F() in class Z1

((Z1)xz1).F1();//calls method F1() in class X

((Z1)xz1).F2b();//calls method F2b() in class Z

((Z1)xz1).F3a();//calls method F3a() in class Z1

Object type casting

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