Suppose that you had the following classes Class D extends B

Suppose that you had the following classes.  

Class D extends B {   /* assume some code here */ }

Class C extends B { /* assume code here */ }

Class B extends A { /* some code here */ }

Class E extends A { /* assume some code here */ }

Class A { /* assume some code here */ }

Further suppose that we have the following variable declarations and assume that they have all been assigned a legal value of the appropriate type.

A [ ]   arrayA = new A[ 20 ];

C [ ]   arrayC = new C[20];

A varA;

B varB;

C varC;

D varD;

E varE;

Circle any of the following pieces of code that would cause compilation errors.

   a-   varA = varE;

b-     varE = varA;

c-     varE = (E )   varA;

d-     for (int x = 0; x < 20; x++ )

                        arrayA[x] = arrayC[x];

   e-   for (int x = 0; x < 20; x++ )

                        arrayC[x] = arrayA[x];

    f-   varB = varE;

   g-    varB = varD;

   h-   arrayC[3] = varC;

   i-   arrayA[5] = varD;

  j-  varA = varD;

Solution

a- varA = varE;
  
   it is fine, because E exteds A, so a Parent class can reference child class object

b- varE = varA;

        Compile Time Error : a child class can not reference its parent without typecasting

c- varE = (E ) varA;

       Fine

d- for (int x = 0; x < 20; x++ )
arrayA[x] = arrayC[x];

Fine. C is child of A

e- for (int x = 0; x < 20; x++ )
arrayC[x] = arrayA[x];

Compile Time Error : a child class can not reference its parent without typecasting

f- varB = varE;

   Compile Error : There is no child/parent relation between B and E

g- varB = varD;
  
   Fine

h- arrayC[3] = varC;

   Fine

i- arrayA[5] = varD;

   Fine. A is parent of D

j- varA = varD;
   Fine. A is parent of D