Part 2
Java interview questions on exception handling covered in this post:
Can we create a custom exception class? If yes then what are the steps
to create a custom exception class?
-
Yes we can create a custom exception class.
-
Please follow the following steps to create your custom
exception.
1.
Create one Custom class and extends the Exception class.
2. Create one String type local variable and assign your custom message to
that variable.
3. Pass the custom message in the Custom class constructor while
instantiating the custom class.
4.
Override toString() method to print the custom message.
5.
We can simply throw a custom exception in any method and pass
a custom message while creating a custom object.
- Please refer to the below example to create a custom exception.
|
package simplifiedjava.crackedInterview; public class CustomException extends Exception { private String message;
public
CustomException(String message) {
this.message
= message; }
public
String toString() {
return
message; }
public
static
void
main(String[] args) {
try
{
if(args.length
>= -1) {
throw
new
CustomException("No Argument Exception");
}
}catch(CustomException e) {
System.out.println(e);
}
}
}
Output: No Argument Exception |
 
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Can you identify which try, catch and finally block combination is
valid?
-
Following are the combinations.
|
1.
try
{
}catch() {
} try { }catch() {
}
2. try { }catch() {
} try { }finally { }
3. try { }
4. try { }finally { }catch() { }
1 and 2 are valid.
3 and 4 are invalid. |
Can we declare an empty catch block?
- Yes you can declare an empty catch block. But it's mandatory to declare any
exception class in the catch block parameter.
-
Please refer to the below example.
|
package simplifiedjava.crackedInterview; public class CustomException extends Exception {
public
static
void
main(String[] args) {
try { }catch(Exception e) {
}
}
}
It is mandatory to declare the Exception class name in the catch
method signature.
But inside the catch block, you can keep it blank. If you missed to
declared an Exception in the catch method signature then you will
get a compile-time error.
|
Can you explain why NullPointerException occurred and how to handle it?
- Calling a method on null reference or trying to access a field of a null
reference will trigger a NullPointerException.
- You can fix it either by making sure you are invoking the method non-null
object.
- Make sure before invoking the method or modifying the field object is
non-null.
-
You can put a null check before invoking or performing any
operation.
-
You may use a try-catch block to handle NullPointerException.
-
Please refer to the below scenario.
a.
Trying to find the length of an array when it is null.
b.
Calling the instance method on the null object.
c.
Trying to modify the field of the null object.
d.
Trying to count a length of String object when it is
null.
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Demo 1: Put null check before invoking or performing any
operation. package simplifiedjava.crackedInterview; public class NullPointerExceptionDemo { String str;
public
static
void
main(String[] args) {
new
NullPointerExceptionDemo().calculateLength(); }
public
void
calculateLength() {
if(str
!= null) {
System.out.println(str.length());
}else
{
System.out.println(" Variable is "+ str);
}
}
}
Output: Variable is null
Demo 2: Put code inside try catch block. package simplifiedjava.crackedInterview; public class NullPointerExceptionDemo { String str;
public
static
void
main(String[] args) {
new
NullPointerExceptionDemo().calculateLength(); }
public
void
calculateLength() {
try
{
str.length();
}catch(NullPointerException e) {
System.out.println("Null Pointer Exception Handled");
}
}
}
Output: Null Pointer Exception Handled |
Can you explain why ClassCastException occurred and how to handle
it?
- When you are trying to cast incompatible objects it triggers
ClassClassException.
- You can say ClassCastException occurs when you are improperly converting a
class from one type to another type.
- When you are trying to convert a Human object into an Animal object which
is incompatible.
- You can use instanceof operator to avoid ClassCastException.
- Please refer to below example to handle ClassCastException.
|
package simplifiedjava.crackedInterview;
import
java.util.ArrayList; import java.util.List; public class ClassCastExceptionHandleDemo {
public
static
void
main(String[] args) {
List objList
= new
ArrayList();
objList.add(new
Integer(10));
objList.add(new
Integer(10));
objList.add(new
Double(10.00)); objList.add(new String("abc"));
for(Object obj: objList) {
if(obj
instanceof
Integer) {
System.out.println("Integer Type");
}else
if(obj
instanceof
Double) {
System.out.println("Double Type");
}else
if(obj
instanceof
String) {
System.out.println("String Type");
}
}
}
}
Output:
Integer Type
Integer Type
Double Type
String Type |
Can you explain why OutOfMemoryError occurred and how to handle
it?
- OutofMemoryError occurs when your program is expecting more memory than JVM
has available.
- OutOfMemoryError normally occurs when you have a code with an infinite
loop.
- You can handle OutOfMemoryError by avoiding infinite loop.
- Allocate more heap space to JVM. Perm-Gen Space must increase but recently
it has changed to meta-space.
Can you explain why StackOverFlowError occurred and how to handle
it?
- StackOverFlowError occurs when the nesting function calls too deeply.
- Generally StackOverFlowError comes in recursion functions. Recursion means
a function calls itself.
- To avoid StackOverFlowError you have to make sure recursive call must
terminate somewhere.
- Please refer to the below example for StackOverFlowerror.
|
package simplifiedjava.crackedInterview; public class StackOverflowErrorDemo {
public
static
void
main(String[] args) {
recursiveFunction(1);
}
public
static
void
recursiveFunction(int
no) {
System.out.println("Number: "
+ no);
if
(no
== 0)
return;
else
recursiveFunction(++no);
}
} Output: Exception in thread "main" java.lang.StackOverflowError |
Can you explain why NoClassDefFoundError occurred?
- Java Virtual Machine is not able to find a particular class at runtime
which was available at compile which triggers NoClassDefFoundError.
- If a class was present during compile time but not available in java
classpath during runtime.
Can you explain why ExceptionInInitializerError occurred?
- Whenever there is an error in the static block ExceptionInInitializerError
will be thrown.
- Generally, this exception will be thrown at the time of class loading
because static block executes at class loading time.
|
package simplifiedjava.crackedInterview;
public
class
ExceptionInInitializerErrorDemo {
static
{
try
{
int
no
= 10/0;
}catch(NullPointerException e) {
e.printStackTrace();
}
}
public
static
void
main(String[] args) {
System.out.println("Main");
}
}
Output: Exception in thread "main"
java.lang.ExceptionInInitializerError
Caused by: java.lang.ArithmeticException: / by zero at
simplifiedjava.crackedInterview.ExceptionInInitializerErrorDemo.<clinit>(ExceptionInInitializerErrorDemo.java:6) |
What's the difference between StackOverflowError and OutOfMemoryError
in java?
-
StackOverflowError:
If there is no memory available in the stack for storing function call or
local variable, JVM will throw StackOverflowError.
-
OutOfMemoryError:
If there is no memory available on heap memory while creating an object then
JVM will throw OutOfMemoryError.
- Java interview questions and answers all MNC - Click here
- Basic core java interview questions and answers for freshers - Click here
- Core java interview questions for 3 years experience - Click here
- Core java interview questions and answers for 3-5 years exp - Click here
- Core java interview questions and Answers for 5 - 7 Years exp - Click here
- Basic Java Interview Questions and Answers - Click here
- Java interview questions and answers on oops - Click here
- Java interview questions and answers on Strings - Click here
- Java interview questions on exception handling - Click here
- Interview questions on multithreading in java for experienced - Click here
- Interview questions on serialization in java for experienced - Click here
- Interview questions on inner class in java for experienced - Click here
- Interview questions on Collections in java for experienced - Click here
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Thank you techies for visiting this blog. I hope you enjoyed this blog and got more technical knowledge. I have tried to cover all types of questions and provided examples tested on eclipse as much as I can. Guys, please don’t just mug up the questions and answers. Try to clear your concepts with examples. Try to write a code on eclipse once you read the concepts. It will help you to memorize the concepts for a very long time. Simultaneously you will be prepared for interview programs as well. It will help you to survive in the IT sector for a long time. It may be easy to crack an interview but it's really tough to survive in the IT industry with inadequate knowledge and skills. I have collected all the questions from actual interviews attended by my friends, colleagues, college mate and classmate. I have covered frequently asked questions as well as challenging questions. I have included many programs to understand the concept thoroughly. I will try to explain the concept with the help of a real-time program in eclipse. You can share more questions which are not covered in this blog or post. Always welcome your suggestions and queries. I will definitely try to resolve it. Please comment your queries and new set of questions under the comment sections. I will create a new post for those questions.
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