Interview Questions and Answers for 'Exception' | Search Interview Question

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Q31. what will be the output ?

class Animal {
public void eat() throws Exception {
}
}

class Dog2 extends Animal {
public void eat(){}
public static void main(){
Animal an = new Dog2();
an.eat();
}
}

Core Java

Ans. Compile Time Error: Unhandled exception type Exception

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Q32. Can finally block throw an exception ?

Core Java

Ans. Yes. Methods invoked from within a finally block can throw an exception. Failure to catch and handle such exceptions results in the abrupt termination of the entire try block.

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Q33. Which exception should be handled in the following code ?

File file = new File("../file.txt");
FileWriter fileWriter = new FileWriter(file);

Core Java

Ans. IOException

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Q34. Which exceptions should be handled with the following code ?

FileOutputStream fileOutputStream = new FileOutputStream(new File("newFile.txt"));

Ans. FileNotFoundException

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Q35. What is the problem with this code ?

class BuggyBread1 {

private BuggyBread2 buggybread2;

public static void main(String[] args){
try {
BuggyBread1 buggybread1 = new BuggyBread1();
ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(new File("newFile.txt")));
objectOutputStream.writeObject(buggybread1);
} catch (Exception e) {
e.printStackTrace();
}
}
}

Core Java

Ans. Though we are trying to serialize BuggyBread1 object but we haven't declared the class to implement Serializable.

This will throw java.io.NotSerializableException upon execution.

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Q36. Will this code run fine if BuggyBread2 doesn't implement Serializable interface ?

class BuggyBread1 implements Serializable{
private BuggyBread2 buggybread2 = new BuggyBread2();

public static void main(String[] args){
try {
BuggyBread1 buggybread1 = new BuggyBread1();
ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(new File("newFile.txt")));
objectOutputStream.writeObject(buggybread1);
} catch (Exception e) {
e.printStackTrace();
}
}
}

Core Java

Ans. No, It will throw java.io.NotSerializableException.

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Q37. How can we protect an application from throwing a NullPointerException ?

Ans. By having Null Checks.

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Q38. What will the following code do ?

String dateStr = "2011 11 19";
DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
Date date = dateFormat.parse(dateStr);
System.out.println(date);

Ans. It will throw the ParseException as the date format doesn't abide with the format of the specified date.

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Q39. Tell me something about AssertionError ?

Core Java

Ans. AssertionError is actually a fatal fault or a bug in the program. We may not like to continue program , request or thread execution if this error occurs as this condition is the assumption to continue further execution.

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Q40. What is CopyOnWriteArrayList ?

Ans. Its a type of ArrayList in which all Write operations , i.e add and set are performed by creating a new copy. This array never changes during the lifetime of the iterator, so it never throws ConcurrentModificationException

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Q41. What are the advantages and disadvantages of CopyOnWriteArrayList ?

Core Java

Ans. This collections class has been implemented in such a manner that it can never throw ConcurrentModificationException. As it performs update and write operations by creating a new copy of ArrayList, It's slower compared to ArrayList.

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Q42. What is ArrayIndexOutOfBoundException ?

Core Java

Ans. Exception thrown by the application is we try to access an element using an index which is not within the range of array i.e lower than 0 or greater than the size of the array.

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Q43. Name few Error and Exception classes provided by Java ?

Ans. http://www.buggybread.com/2015/01/java-list-of-error-exception-classes.html

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Q44. In which cases isn't instanceof operator a bad practice?

Core Java

Ans. To avoid ClassCastException.

Though the following code will compile fine but will result in ClassCastException during runtime.

Fruit fruit = new Apple();
Banana banana = Banana(fruit); // ClassCastException

This code will not give compile time error as Banana and Fruit are related as Banana either extends or implement Fruit, So downcasting is acceptable. With this code we assume that the Fruit handler will have the Apple object at that point, violating which the code will throw the exception.

This exception can be avoided by following code.

Fruit fruit = new Apple();
if(fruit instanceOf Banana){
Banana banana = Banana(fruit); // ClassCastException
}

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Q45. What is OutOfMemoryError in Java?

Core Java

Ans. OutOfMemoryError in Java is a subclass of VirtualMachineError and is thrown by JVM when it runs out of heap memory.

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Q46. Which interfaces are implemented by BatchUpdateException?

Ans. [Iterable]

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Q47. Which of the following is not possible ?

a. try block followed by catch
b. try block followed by finally
c. try block followed by catch block and then finally
d. try block without catch or finally block

Ans. try block without catch or finally block

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Q48. Invoking start twice on same thread leads to ..

a. ClassCastException
b. NullPointerException
c. InterruptedException
d. IllegalStateException

Ans. IllegalStateException

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Q49. What are the fail safe systems ?

Operating System

Ans. Fail Safe systems are tolerant systems that continue processing even if they sense any problem. the objective here is to continue with the processing even if there are some problems instead of completely shutting it down. Example could be to catch an exception and still letting it complete with partial results.

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Q50. Explain Exception Hierarchy in Java SE ?

Core Java

Ans. <a href="http://www.programcreek.com/2009/02/diagram-for-hierarchy-of-exception-classes/" rel="nofollow">http://www.programcreek.com/2009/02/diagram-for-hierarchy-of-exception-classes/</a>

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Q51. Can we have try statement without catch? If try statement contains return will the finally block be executed? What happens if there is an exception inside finally block?

Core Java

Ans. Yes, with finally.

Yes, finally block will be executed even if there is no exception in try block.

If finally throws an exception, the exception gets thrown to the calling module.

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Q52. What happens to the Exception object after the exception handling is done ?

Core Java

Ans. As with all other objects its garbage collected after its usage unless its rethrown.

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Q53. How can we catch an exception thrown by another thread ?

Core Java

Ans. http://stackoverflow.com/a/6548203/2789764

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Q54. What is Java NumberFormatException ?

Core Java

Ans. NumberFormatException is the exception that Java throws when we try to convert one data type to the Number data type but the value is not parsable to be a Number.

For example , the following code will result in the NumberFormatException

String string = "Buggy";
int strtoInt = Integer.parseInt(string);

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Q55. Difference between Error and Exception ?

Core Java

Ans. An Error indicates serious problems that a reasonable application should not try to catch whereas

An Exception indicates conditions that a reasonable application might want to catch.

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Q56. What is the difference between following code segments

1.

try {
for(int i=0;i<100;i++){
calculate(i);
}
} catch (Exception ex) {
System.out.println("Error while processing")
}

and

2.

for(int i=0;i<100;i++){
try {
calculate(i);
} catch (Exception ex) {
System.out.println("Error while processing")
}
}

Core Java

Ans. In first case the whole loop will terminate as soon as any exception happens in the method calculate ( assuming calculate method is not handling its exception and those are thrown back at the calling method )

In Second case exception will be caught for individual iteration and hence it wont break the loop and will continue for the next iteration.

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Q57. What is an exception and exception handling in Java ?

Core Java

Ans. An Exception in java is the occurrence during computation that is anomalous and is not expected.

Exception handling is the mechanism which is used to handle such situations.

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Q58. What are the different ways to handle an exception ?

Core Java

Ans. 1. Wrap the desired code in try block followed by a catch / finally to catch the exception

2. Declare the throws clause with exceptions that the code is expected to throw as an indication to the calling method to take care of it.

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Q59. How should we handle errors while writing or accessing Stored Procedures?

Database

Ans. Store Procedure returns the error code. Moreover we can put the call withing try block and catch SQL Exception.

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Q60. Can we have only try block in java ?

Core Java

Ans. No, It should be followed by either catch or finally.

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