Core Java - Interview Questions and Answers for 'Error' | Search Interview Question

Core Java - Interview Questions and Answers for 'Error' - 16 question(s) found - Order By Newest

Q1. Explain java.lang.OutOfMemoryError ?

Ans. This Error is thrown when the Java Virtual Machine cannot allocate an object because it is out of memory, and no more memory could be made available by the garbage collector.

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Q2. When do you get ClassCastException?

or

What is ClassCastException ?

Ans. As we only downcast class in the hierarchy, The ClassCastException is thrown to indicate that code has attempted to cast an object to a subclass of which it is not an instance.

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Q3. Differences between class not found exception and noclassdef found error ?

Core Java

Ans. ClassNotFoundException is an exception that occurs when we try to load a class at run time using Class.forName() or loadClass() methods and mentioned classes are not found in the classpath.

NoClassDefFoundError is an error that occurs when a particular class is present at compile time, but was missing at run time.

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Q4. What are some different logging levels for log4j ?

Log4j

Ans. DEBUG
ERROR
ALL
WARN
INFO
FATAL
OFF
TRACE
TRACE_INT
WARN

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Q5. Which of the following exception is thrown when we try to access element which is beyond the size ?

a. NullPointerException
b. ArrayIndexOutOfBoundException
c. ArithmeticException
d. ParseException

Ans. ArrayIndexOutOfBoundException

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Q6. What will happen if static modifier is removed from the signature of the main method?

Ans. Program throws "NoSuchMethodError" error at runtime .

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Q7. 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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Q8. Will this code compile ?

public class BuggyBread1{
abstract public void test();
}

Core Java

Ans. No. It will give the compilation error saying "The abstract method test in type BuggyBread1 can only be defined by an abstract class".

We need to declare the class abstract for it to have any abstract method.

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Q9. Will this Code compile ?

abstract public class BuggyBread1{
abstract public void test(){};
}

Core Java

Ans. No. This will give a compilation error saying "Abstract methods do not specify a body".

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Q10. 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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Q11. 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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Q12. When do we generally get this database error - integrity constraint violated - parent key not found ?

Ans. This error most likely will be thrown during an insert statement, while inserting a value within a foreign key column which doesnt exist within the Parent column. For example - Trying to add a dept number reference within a Employee Table when the Dept doesnt exist in the Dept Table.

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Q13. When do we generally get the database error - Unique Constraint Violated ?

Ans. This error can result either on an insert, update or delete when any change in data results in duplicate record or subset of it having unique constraint on record or its subset. For example - If we have a unique constraint on a combination of columns and then trying to insert duplicate column values.

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Q14. 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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Q15. Can we catch errors in Java ?

Core Java

Ans. Yes we can

try {
// code
} catch (Error ex) {
// handling code
}

but we shouldn't ideally do that as errors are mostly JVM based and not application based and there is rarely we can do something about it. Very likely catching and not re throwing would lead to muting their response or trace.

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Q16. What is the difference between access and error log ?

Logging

Ans. We log each access to the application resource within access logs, something like

"GET / HTTP/1.0" 200 113 "-" "Mozilla/5.0 zgrab/0.x" "-"

We log only error / warn messages within error logs, something like

ERROR 123#0: *19 connect() failed

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