UGC NET Computer Science Object Oriented Programming OOPs Previous Year Questions (PYQs) – Page 1 of 3

Let the boxes be $B_1, B_2, B_3$ and event $E$ be drawing $1$ white and $1$ red ball.

Since one box is chosen randomly,

$P(B_1)=P(B_2)=P(B_3)=\frac{1}{3}$

For first box,

$P(E|B_1)=\frac{\binom{2}{1}\binom{4}{1}}{\binom{9}{2}}=\frac{8}{36}=\frac{2}{9}$

For second box,

$P(E|B_2)=\frac{\binom{3}{1}\binom{2}{1}}{\binom{7}{2}}=\frac{6}{21}=\frac{2}{7}$

For third box,

$P(E|B_3)=\frac{\binom{4}{1}\binom{3}{1}}{\binom{8}{2}}=\frac{12}{28}=\frac{3}{7}$

Using Bayes theorem,

$P(B_1|E)=\frac{P(B_1)P(E|B_1)}{P(B_1)P(E|B_1)+P(B_2)P(E|B_2)+P(B_3)P(E|B_3)}$

$P(B_1|E)=\frac{\frac{1}{3}\times\frac{2}{9}}{\frac{1}{3}\times\frac{2}{9}+\frac{1}{3}\times\frac{2}{7}+\frac{1}{3}\times\frac{3}{7}}$

$P(B_1|E)=\frac{\frac{2}{9}}{\frac{2}{9}+\frac{2}{7}+\frac{3}{7}}$

$P(B_1|E)=\frac{\frac{2}{9}}{\frac{59}{63}}=\frac{14}{59}=0.237$

Here, the class has a method

$equals(Good\ n)$

This method does not override the original $equals(Object)$ method of Java because the parameter type is $Good$, not $Object$.

For Line 1:

$m1.equals(m2)$

Here both are objects of class $Good$, so $equals(Good\ n)$ is called.

Both values are $22$, so output is

$True$

For Line 2:

$s1.equals(s2)$

Here $s1$ and $s2$ are declared as $Object$ type.

So, Java calls $Object$ class $equals()$ method, which compares references.

Since both are different objects, output is

$False$

For Line 3:

$m1.equals(s2)$

Here $s2$ is of type $Object$, so $equals(Good\ n)$ is not called.

It calls $equals(Object)$, so reference comparison is done.

Output is

$False$

For Line 4:

$s1.equals(m2)$

Here $s1$ is of type $Object$, so again $Object$ class $equals()$ method is called.

Output is

$False$

Therefore, output is:

$True,\ False,\ False,\ False$

Python → OOP

Smalltalk → pure OOP

Perl → supports OOP

SQL Plus → database query interface.

In protected inheritance:

Public members of base class become protected members in derived class.

Protected members of base class also remain protected in derived class.

Private members of base class are not directly accessible in derived class.

So, member functions of class $B$ can access public and protected members of class $A$.

But object of class $B$ cannot access public base class data directly, because it becomes protected after protected inheritance.

JVM executes Java bytecode.

For execution, JVM mainly needs:

Class loader to load the class files

Java Interpreter to interpret and execute bytecode

So, JVM needs class loader and Java interpreter.