Object Oriented Programming | OOP | MCQ

Q 1. What is the output of the following
StringBuffer sb1 = new StringBuffer(“Amit”);
StringBuffer sb2= new StringBuffer(“Amit”);
String ss1 = “Amit”;
System.out.println(sb1==sb2);
System.out.println(sb1.equals(sb2));
System.out.println(sb1.equals(ss1));
System.out.println(“Poddar”.substring(3));
Ans:
a) false
false
false
dar
b) false
true
false
Poddar
c) Compiler Error
d) true
true
false
dar
Correct Answer is a)
***** Look carefully at code and answer the following questions ( Q2 to Q8)
1     import java.applet.Applet;
2    import java.awt.*;
3    import java.awt.event.*;
4     public class hello4 extends Applet {
5       public void init(){
6           add(new myButton(“BBB”));
7     }
8       public void paint(Graphics screen) {
9   }
10       class myButton extends Button{
11             myButton(String label){
12                super(label);
13            }
14           public String paramString(){
15                return super.paramString();
16              }
17     }
18   public static void main(String[] args){
19        Frame myFrame = new Frame(
20                           “Copyright Amit”);
21      myFrame.setSize(300,100);
22     Applet myApplet = new hello4();
23     Button b = new Button(“My Button”);
24     myApplet.add(b);
25     b.setLabel(b.getLabel()+”New”);
26    // myButton b1 =(new hello4()).new myButton(“PARAMBUTTON”);
27     System.out.println(b1.paramString());
28     myFrame.add(myApplet);
29     myFrame.setVisible(true);
30     myFrame.addWindowListener(new WindowAdapter(){
31              public void windowClosing(WindowEvent e){
32                                       System.exit(0);}});
33   }
34 } //End hello4 class.
Q2. If you run the above program via appletviewer ( defining a HTML file), You see on screen.
a) Two buttons
b) One button with label as “BBB”
c) One button with label as “My ButtonNew”
d) One button with label as “My Button”
Correct answer is b)
Q3. In the above code if line 26 is uncommented  and program runs as standalone application

1. a) Compile Error
   b) Run time error
   c) It will print the the label as PARAMBUTTON for button b1

Correct answer is c)
Q4 In the code if you compile as “javac hello4.java” following files will be generated.
a) hello4.class, myButton.class,hello41.class
b)hello4.class, hello4$myButton.class,hello4$1.class
c)hello4.clas,hello4$myButton.class
Correct answer is b)
Q5. If above program is run as a standalone application. How many buttons will be displayed

1. a) Two buttons
   b) One button with label as “BBB”
   c) One button with label as “My ButtonNew”
   d) One button with label as “My Button”

correct answer is C)
Q6. If from line no 14 keyword “public” is removed, what will happen.( Hint :paramString() method in java.awt.Button  is a protected method. (Assume line 26 is uncommented)

1. a) Code will not compile.
   b) Code will compile but will give a run time error.
   c) Code will compile and no run time error.

Correct answer is a). As you can not override a method with weaker access privileges
Q7.  If from line no 14 keyword “public” is replaced with “protected”, what will happen.(Hint :paramString() method in java.awt.Button is a protected method.(Assume line 26 is uncommented)

1. a) Code will not compile.
   b) Code will compile but will give a run time error.
   c) Code will compile and no run time error.

Correct answer is c) . As you can access a protected variable in the same package.
Q8.If line no 26 is replaced with Button b1 = new Button(“PARAMBUTTON”).(Hint :paramString() method in java.awt.Button is a protected method.(Assume line 26 is uncommented)

1. a) Code will not compile.
   b) Code will compile but will give a run time error.
   c) Code will compile and no run time error.

Correct answer is a) Because protected variables and methods can not be accssed in another package directly. They can only be accessed if the class is subclassed and instance of subclass is used.
Q9. What is the output of following if the return value is “the value 0 if the argument string is equal to this string; a value less than 0 if this string is lexicographically less than the string argument; and a value greater than 0 if this string is lexicographically greater than the string argument”  (Assuming  written inside main)
String s5 = “AMIT”;
String s6 = “amit”;
System.out.println(s5.compareTo(s6));
System.out.println(s6.compareTo(s5));
System.out.println(s6.compareTo(s6));
Ans
a> -32
32
b>  32
32
c>  32
-32
d>  0
Correct Answer is a)
Q10) What is the output  (Assuming  written inside main)
String s1 = new String(“amit”);
String s2 = s1.replace(‘m’,’i’);
s1.concat(“Poddar”);
System.out.println(s1);
System.out.println((s1+s2).charAt(5));

1. a) Compile error
   b) amitPoddar
   o
   c) amitPoddar
   i
   d) amit
   i

Correct answer is d)As String is imutable.so s1 is always “amit”. and s2 is “aiit”.
Q11) What is the output  (Assuming  written inside main)
String s1 = new String(“amit”);
System.out.println(s1.replace(‘m’,’r’));
System.out.println(s1);
String s3=”arit”;
String s4=”arit”;
String s2 = s1.replace(‘m’,’r’);
System.out.println(s2==s3);
System.out.println(s3==s4);

1. a)  arit
   amit
   false
   true
   b)  arit
   arit
   false
   true
   c)  amit
   amit
   false
   true
   d)  arit
   amit
   true
   true
   Correct answer is a)  s3==s4 is true because java points both s3 and s4 to same memory location in string pool

Q12) Which one does not extend java.lang.Number
1)Integer
2)Boolean
3)Character
4)Long
5)Short
Correct answer is  2) and 3)
Q13) Which one does not have a valueOf(String) method
1)Integer
2)Boolean
3)Character
4)Long
5)Short
Correct answer is 3)
Q.14) What is the output of following (Assuming  written inside main)
String s1 = “Amit”;
String s2 = “Amit”;
String s3 = new String(“abcd”);
String s4 = new String(“abcd”);
System.out.println(s1.equals(s2));
System.out.println((s1==s2));
System.out.println(s3.equals(s4));
System.out.println((s3==s4));
a)  true
true
true
false
b)  true
true
true
true
c)  true
false
true
false
Correct answer is a)
Q15. Which checkbox will be selected in the following code ( Assume with main and added to a Frame)
Frame myFrame = new Frame(“Test”);
CheckboxGroup  cbg = new CheckboxGroup();
Checkbox cb1 = new Checkbox(“First”,true,cbg);
Checkbox cb2 = new Checkbox(“Scond”,true,cbg);
Checkbox cb3 = new Checkbox(“THird”,false,cbg);
cbg.setSelectedCheckbox(cb3);
myFrame.add(cb1);
myFrame.add(cb2);
myFrame.add(cb3);
a)     cb1
b)     cb2,cb1
c)     cb1,cb2,cb3
d)     cb3
Correct Answer is d) As in a CheckboxGroup only one can be selected
Q16) Which checkbox will be selected in the following code ( Assume with main and added to a Frame)
Frame myFrame = new Frame(“Test”);
CheckboxGroup  cbg = new CheckboxGroup();
Checkbox cb1 = new Checkbox(“First”,true,cbg);
Checkbox cb2 = new Checkbox(“Scond”,true,cbg);
Checkbox cb3 = new Checkbox(“THird”,true,cbg);
myFrame.add(cb1);
myFrame.add(cb2);
myFrame.add(cb3);
a)     cb1
b)     cb2,cb1
c)     cb1,cb2,cb3
d)     cb3
Correct Answer is d) As in a CheckboxGroup only one can be selected
Q17) What will be the output of line 5
1 Choice c1 = new Choice();
2 c1.add(“First”);
3 c1.addItem(“Second”);
4 c1.add(“Third”);
5 System.out.println(c1.getItemCount());
a)    1
b)    2
c)    3
d)    None of the above
Correct Answer is c)
Q18) What will be the order of four items added
Choice c1 = new Choice();
c1.add(“First”);
c1.addItem(“Second”);
c1.add(“Third”);
c1.insert(“Lastadded”,2);
System.out.println(c1.getItemCount());
a)    First,Second,Third,Fourth
b)    First,Second,Lastadded,Third
c)    Lastadded,First,Second,Third
Correct ANswer is b)
Q19) Answer based on following code
1 Choice c1 = new Choice();
2 c1.add(“First”);
3 c1.addItem(“Second”);
4 c1.add(“Third”);
5 c1.insert(“Lastadded”,1000);
6 System.out.println(c1.getItemCount());

1. a)   Compile time error
   b)    Run time error at line 5
   c)   No error and line 6 will print 1000
   d)   No error and line 6 will print 4

Correct ANswer is d)
Q20) Which one of the following does not extends java.awt.Component

1. a) CheckBox
   b) Canvas
   c) CheckbocGroup
   d) Label

Correct answer is c)
Q21) What is default layout manager for panels and applets?
a) Flowlayout
b) Gridlayout
c) BorderLayout
Correct answer is a)
Q22) For awt components which of the following statements are true?

1. a) If a component is not explicitly assigned a font, it usese the same font that it container uses.
   b) If a component is not explicitly assigned a foreground color , it usese the same foreground color  that it container uses.
   c) If a component is not explicitly assigned a backround color , it usese the same background color  that it container uses.
   d) If a component is not explicitly assigned a layout manager , it usese the same layout manager  that it container uses.

correct answer is a),b),c)
Q23)java.awt.Component class method getLocation() returns Point (containg x and y cordinate).What does this x and y specify

1. a) Specify the postion of components lower-left component in the coordinate space of the component’s parent.
   b) Specify the postion of components upper-left component in the coordinate space of the component’s parent.
   c) Specify the postion of components upper-left component in the coordinate space of the screen.

correct answer is b)
Q24. What will be the output of follwing
{
double d1 = -0.5d;
System.out.println(“Ceil for d1 ” + Math.ceil(d1));
System.out.println(“Floor for d1 ” +Math.floor(d1));
}
Answers:
a)  Ceil for d1 0
Floor for d1 -1;
b)  Ceil for d1 0
Floor for d1 -1.0;
c)  Ceil for d1 0.0
Floor for d1 -1.0;
d)  Ceil for d1 -0.0
Floor for d1 -1.0;
correct answer is d) as 0.0 is treated differently from -0.0
Q25. What is the output of following
{
float f4 = -5.5f;
float f5 = 5.5f;
float f6 = -5.49f;
float f7 = 5.49f;
System.out.println(“Round f4 is ” + Math.round(f4));
System.out.println(“Round f5 is ” + Math.round(f5));
System.out.println(“Round f6 is ” + Math.round(f6));
System.out.println(“Round f7 is ” + Math.round(f7));
}
a)Round f4 is -6
Round f5 is 6
Round f6 is -5
Round f7 is 5
b)Round f4 is -5
Round f5 is 6
Round f6 is -5
Round f7 is 5
Correct answer is b)
Q26. Given Integer.MIN_VALUE = -2147483648
Integer.MAX_VALUE = 2147483647
What is the output of following
{
float f4 = Integer.MIN_VALUE;
float f5 = Integer.MAX_VALUE;
float f7 = -2147483655f;
System.out.println(“Round f4 is ” + Math.round(f4));
System.out.println(“Round f5 is ” + Math.round(f5));
System.out.println(“Round f7 is ” + Math.round(f7));
}
a)Round f4 is -2147483648
Round f5 is 2147483647
Round f7 is -2147483648
b)Round f4 is -2147483648
Round f5 is 2147483647
Round f7 is -2147483655
correct answer is a)
//Reason If the argument is negative infinity or any value less than or equal to the value of Integer.MIN_VALUE, the result is
equal to the value of Integer.MIN_VALUE.
If the argument is positive infinity or any value greater than or equal to the value of Integer.MAX_VALUE, the result is
equal to the value of Integer.MAX_VALUE. // From JDK api documentation
Q27)
1 Boolean b1 = new Boolean(“TRUE”);
2 Boolean b2 = new Boolean(“true”);
3 Boolean b3 = new Boolean(“JUNK”);
4 System.out.println(“” + b1 + b2 + b3);

1. a) Comiler error
   b) RunTime error
   c)truetruefalse
   d)truetruetrue

Correct answer is c)
Q28) In the above question if line 4 is changed to
System.out.println(b1+b2+b3); The output is
a) Compile time error
b) Run time error
c) truetruefalse
d) truetruetrue
Correct answer is a) As there is no method to support  Boolean + Boolean
Boolean b1 = new Boolean(“TRUE”);
 Think —–>System.out.println(b1); // Is this valid or not?
Q29. What is the output
{
Float f1 = new Float(“4.4e99f”);
Float f2 = new Float(“-4.4e99f”);
Double d1 = new Double(“4.4e99”);
System.out.println(f1);
System.out.println(f2);
System.out.println(d1);
}

4. a) Runtime error
   b) Infinity
   -Infinity
   4E99
   c) Infinity
   -Infinity
   Infinity
   d) 4.4E99
   -4.4E99
   4.4E99

Correct answer is b)
Q30 Q. Which of the following wrapper classes can not
take a “String” in constructor
1) Boolean
2) Integer
3) Long
4) Character
5) Byte
6) Short
correct answer is 4)
Q31. What is the output of following
Double d2 = new Double(“-5.5”);
Double d3 = new Double(“-5.5”);
System.out.println(d2==d3);
System.out.println(d2.equals(d3));

1. a)  true
   true
   b)  false
   false
   c)  true
   false
   d)  false
   true

Correct answer is d)
Q32) Which one of the following always honors the components’s preferred size.
a) FlowLayout
b) GridLayout
c) BorderLayout
Correct answer is a)
Q33) Look at the following code
import java.awt.*;
public class visual extends java.applet.Applet{
static Button b = new Button(“TEST”);
public void init(){
add(b);
}
public static void main(String args[]){
Frame f = new Frame(“Visual”);
f.setSize(300,300);
f.add(b);
f.setVisible(true);
}
}
What will happen if above code is run as a standalone application

1. a) Displays an empty frame
   b) Displays a frame with a button covering the entire frame
   c) Displays a frame with a button large enough to accomodate its label.

Correct answer is b) Reason- Frame uses Border Layout which places the button to CENTRE
 (By default) and ignores Button’s preferred size.
Q34  If the code in Q33 is compiled and run  via appletviewer what will happen
a) Displays an empty applet
b) Displays a applet with a button covering the entire frame
c) Displays a applet with a button large enough to accomodate its label.
Correct answer is c) Reason- Applet uses FlowLayout which honors  Button’s preferred size.
Q35. What is the output
public static void main(String args[]){
Frame f = new Frame(“Visual”);
f.setSize(300,300);
f.setVisible(true);
Point p =  f.getLocation();
System.out.println(“x is ” + p.x);
System.out.println(“y is ” + p.y);
}

1. a) x is 300
   y is 300
   b) x is 0
   y is 0
   c) x is 0
   y is 300

correct answer is b) Because postion is always relative to parent container and in this
    case Frame f is the topemost container
Q36) Which one of the following always ignores the components’s preferred size.
a) FlowLayout
b) GridLayout
c) BorderLayout
Correct answer is b)
Q37) Consider a directory structure like this (NT or 95)
C:\JAVA\12345.msg  –FILE
\dir1\IO.class  — IO.class is under dir1
Consider the following code
import java.io.*;
public class IO {
public static void main(String args[]) {
File f = new File(“..\\12345.msg”);
try{
System.out.println(f.getCanonicalPath());
System.out.println(f.getAbsolutePath());
}catch(IOException e){
System.out.println(e);
}
}
}
What will be the output of running “java IO” from C:\java\dir1
a)  C:\java\12345.msg
C:\java\dir1\..\12345.msg

12345. b)  C:\java\dir1\12345.msg
       C:\java\dir1\..\12345.msg
12346. c)  C:\java\dir1\..\12345.msg
       C:\java\dir1\..\12345.msg

correct answer is a) as getCanonicalPath Returns the canonical form of this File object’s pathname. The precise definition of canonical form is system-dependent, but it usually
specifies an absolute pathname in which all relative references and references to the current user directory have been completely resolved.
WHERE AS
getAbsolutePath Returns the absolute pathname of the file represented by this object. If this object represents an absolute pathname, then return the pathname. Otherwise, return a pathname that is a concatenation of the current user directory, the separator character, and the pathname of this file object.
Q38) Suppose we copy IO.class from C:\java\dir1 to c:\java
What will be the output of running “java IO” from C:\java.
a)  C:\java\12345.msg
C:\java\..\12345.msg

12345. b)  C:\12345.msg
       C:\java\..\12345.msg
12346. c)  C:\java\..\12345.msg
       C:\java\\..\12345.msg

correct answer is b)
Q39) Which one of the following methods of java.io.File throws IOException and why

1. a) getCanonicalPath and getAbsolutePath both require filesystem queries.
   b) Only getCannonicalPath as it require filesystem queries.
   c) Only getAbsolutePath as it require filesystem queries.

Correct answer is b)
Q40) What will be the output  if
Consider a directory structure like this (NT or 95)
C:\JAVA\12345.msg  –FILE
\dir1\IO.class  — IO.class is under dir1
import java.io.*;
public class IO {
public static void main(String args[]) {
File f = new File(“12345.msg”);
String arr[] = f.list();
System.out.println(arr.length);
}
}

12345. a) Compiler error as 12345.msg is a file not a directory
       b) java.lang.NullPointerException at run time
       c) No error , but nothing will be printed on screen

Correct ansewer is b)
Q41) What will be the output
Consider a directory structure like this (NT or 95)
C:\JAVA\12345.msg  –FILE
import java.io.*;
public class IO {
public static void main(String args[]) {
File f1 = new File(“\\12345.msg”);
System.out.println(f1.getPath());
System.out.println(f1.getParent());
System.out.println(f1.isAbsolute());
System.out.println(f1.getName());
System.out.println(f1.exists());
System.out.println(f1.isFile());
}
}

12345. a) \12345.msg
       \
       true
       msg
       true
       true
12346. b) \12345.msg
       \
       true
       \12345.msg
       false
       false
12347. c) 12345.msg
       \
       true
       msg
       false
       false
       d) \12345.msg
       \
       true
       12345.msg
       false
       false

correct answer is d)
Q42) If in question no 41 the line
File f1 = new File(“\\12345.msg”); is replaced with File f1 = new File(“12345.msg”);
What will be the output

12345. a) 12345.msg
       \
       true
       msg
       true
       true
12346. b) 12345.msg
       null
       true
       msg
       true
       true
12347. c) 12345.msg
       null
       false
       msg
       true
       true
12348. d) \12345.msg
       \
       true
       msg
       false
       false

Correct answer is c)
Which Control Statements allow the program to choose different paths of execution?
Selection
Which Control Statements enable program execution to repeat one or more statements?
Iteration
The switch statement does not require a break.
False
In Interface we need not use the keyword abstract for the methods.
True
What are the Logical operators?
OR(|) , AND(&) , XOR(^)
Byte can be Cast to Double Value.
True
Which thread is created automatically when the program is started?
Main thread
Nested if is less efficient then switch statement.
True
________ are stored in hierarchical manner.
Packages
The mechanism by which java frees the memory occupied by unused objects is ________.
Garbage Collection
When you implement an interface method, it must be declared as :-
Public
What are primitive data types?
byte, short, int, long
In While loop condition can be any Boolean expression
True
Long makes it useful when big ________ numbers are needed.
Whole
Which Control Statement allow the program to execute in a non-linear fashion?
Jump
With java Type Casts are checked at both compile-time and runtime.
True
Java defines two ways when instantiating an object, such as :-
Can implement the runnable interface , Can extend the thread class
The explicit drop of an object reference by setting the value of a variable, whose data type is a reference type of ________.
Null
What is a string?
A combination of characters called as string
What are the programming constructs?
Sequential , Selection — if and switch statements , Iteration — for loop, while loop and do-while loop
What can be created by instantiating an object type thread?
Thread
In ________ statement the value of the expression is compared with each of the literal values in case statements.
Switch
How to declare an interface example?
access class classname implements interface.
Integer can Cast to byte value.
False
Transient variable is variable that may not be serialized.
True
Using which keyword we can fully abstract a class?
interface
The ________ loop repeats a set of statements a certain number of times until a condition is matched.
For
There are ________ kinds of Floating point type
Two
By default, all program import the java.lang package.
True
What returns a reference to the thread in which it is called?
Method , Class , Object
Do while loop always executes its body at least once, because its conditional expression is at the bottom of the loop.
True
Which statements can be used with the java’s loop?
Jump , Continue , Break
________ are containers for classes.
Packages
Java’s multithreading system is built upon :-
Thread class , Its methods , Companion interface
The default encoding of objects supports the ________ of the classes.
Evolution
Which are the keywords use in switch statement?
Case , Default
A Java application can execute anywhere on the network, this implements that Java is :-
Architecture neutral
Boolean values can be cast into any other primitive type.
False
Which one does not extend java.lang.Number?
Boolean , Character
The smallest integer type is ________.
Byte
Which is a public static member of thread?
currenthread( ) , mainthread( )
Casting does not affect the original object or value.
True
Anything declared ________ can be accessed from anywhere within program.
Public
Which method is used to determine the class of an object?
getClass( ) method
Method definition has four parts, they are :-
Name of the method , Type of object , List of parameters
Object oriented programming organizes a program around processes acting on data.
False
What are the possible access modifiers while implementing interface methods?
public
Which statement defines a name space in which classes are stored?
package
Which statement is used to explicitly return from a method?
Return
There are two distinct types of multitasking. Which are those?
Process based , Thread-base
Exit statement is optional in which loops in java?
While , Do-while , For