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

Interview Questions and Answers - Order By Newest

Q611. public class BuggyBread1{

public static void main (String args[]) {
Set<Integer> mySet = new TreeSet<Integer>();
mySet.add(1);
mySet.add(2);
mySet.add(111);
for(Integer d: mySet){
System.out.println(d);
}
}
}

Core Java

Ans. 1
2
111

TreeSet maintains the elements in the ascending order which is identified by the compareTo method. compareTo method in Integer has been defined such that it results in the natural numerical Order.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java code coding set treeset}

Q612. Can we extend an Enum ?

Core Java

Ans. No. Enums are final by design.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java enums inheritance object oriented programming (oops) oops concepts yes-no Asked in 1 Companies intermediate}

Q613. How can we change the JDK compliance level ?

Eclipse

Ans. Windows -> Preferences -> Java - Compiler -> Java Compliance Level

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve eclipse jdk compliance level eclipse java}

Q614. Can I use different Java versions for building different Eclipse projects ?

Eclipse

Ans. Yes. We can assign different JRE System libraries by going to

Java Build Path -> Libraries

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java eclipse jre library}

Q615. 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.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java error exceptions exception handling assertion error assertionerror}

Q616. Should we create system software ( e.g Operating system ) in Java ?

Core Java

Ans. No, Java runs on a virtual machine called JVM and hence doesn't embed well with the underlying hardware. Though we can create a platform independent system software but that would be really slow and that's what we would never need.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java system software java jvm yes-no yes no java operating system architecture}

Q617. What is Java primarily used for ?

Core Java

Ans. For creating platform independent software applications.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java java use architecture}

Q618. Shall we keep the enumeration name in all capital letters as it contains all constants ?

Ans. Enum is actually a class with pre defined constants. So enum name should follow the convention of the Class name. Though the constant names or the Enum variables should follow the convention of having all capital letters.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java enum enumerations java conventions java naming conventions}

Q619. In majority of the situations it won't make much sense whether you append this with the instance method call.Can you tell a situation wherein this keyword would make sense in a instance method ?

Core Java

Ans. Within instance method of the parent class that has other multiple methods that have been overridden by the derived classes.

In such case a simple method call from the common method will always be made to the method definition in the parent class. But If we use this.methodCall , this will be polymorphic and will be made to the respective derived object overriding method.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java this keyword java keywords}

Q620. Why is null == null returns true ?

Core Java

Ans. Any reference in java that doesn't point to any object , gets assigned null i.e is a reference to null. Two object references in java are treated equal if they point to the same memory. That's Why null == null results true.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java null equality references}

Q621. How is HashSet maintained in memory by Java ?

Core Java

Ans. HashSet is maintained as HashMap by Java with values of the HashSet as Keys of the HashMap and value of the HashMap as the constant PRESENT.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve ebay java collections hashset hashmap expert}

Q622. What is Closeable ?

Core Java

Ans. A Closeable is an interface which is a source or destination of data that can be closed.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve closeable interfaces intermediate rare}

Not frequently asked as it was introduced with Java 8.

Q623. What is the @FunctionalInterface annotation ?

Core Java

Ans. This is an informative annotation that specify that the interface is a functional interface. A Function Interface has only one abstract method and many default methods. Compiler generates an error if the interface specified with the annotation doesn't abide by the specifications for functional interface.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java java8 java 8 functional interface default methods}

Q624. Name some Java REST services frameworks ?

Rest

Ans. Jersey , Restlet , RestX, Spring , RestEasy ,Restfulie, Play Framework

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java rest web services frameworks}

Q625. Is this valid in Java ?

Long x = new Long ("42");

Core Java

Ans. Yes. Long wrapper class has overloaded constructor which takes String as input and then translate it to the long value and stored it as long.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java wrapper classes long wrapper class long}

Q626. What is classpath in a project?

Core Java

Ans. ClassPath is the path where Java looks for class files to resolve the dependencies. For example - If you are using a class "xyz" in your code and have specified the respective import, Where should Java look for the definition of xyz. Java determines using the class path settings.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java classpath classpath settings Asked in 2 Companies}

Q627. Why is a constant defined as a static final in Java?

Core Java

Ans. Final makes sure that the value doesn't change after initialization and static makes sure that there is only one copy that can be shared across objects.

Making it non static will unnecessarily create a different copy per object wherein the same value will kept for all copies ( as its final and cannot be changed ).

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java static final variables variable constants basic frequent}

Q628. What is the difference between public class and class ?

Core Java

Ans. Class without any access specifier has the default scope i.e it can be accessed by any class within same package.

Class declared public can be accessed from anywhere.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java access specifier access modifiers public class class}

Try 1 Question(s) Test

Q629. 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.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java oops abstract class abstract methods java compilation error}

Q630. 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".

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java abstract classes abstract methods java compilation error java coding java code coding yes-no}

Q631. Give an Example for Builder Pattern ?

Core Java

Ans. String str = new StringBuilder().append("Buggy").append("Bread").toString();

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java builder pattern design pattern stringbuilder string Asked in 3 Companies}

Try 1 Question(s) Test

Q632. Is this Polymorphism ?

Map<String, List<String>> inventoryManagerCountMap = new HashMap<String, ArrayList<String>>();

Core Java

Ans. No. This will result in compilation error as Polymorphism cannot be performed on Object types.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java polymorphism object oriented programming (oops) oops concepts}

Rarely asked as it was introduced with Java 8.

Q633. Difference between DoubleSummaryStatistics , IntSummaryStatistics and LongSummaryStatistics ?

Core Java

Ans. They all does the same task i.e to compute statistical information on the stream of data. They differ by the way they store the statistical information as they expect a different data type of the values being used.

IntSummaryStatistics and LongSummaryStatistics expect non floating point values and hence stores the statistical information like min,max and sum as non floating values ( int or long ) whereas DoubleSummaryStatistics stores these information as floating value.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java java8 java 8 lambda expressions doublesummarystatistics intsummarystatistics longsummarystatistics summarystatistics}

Q634. Have you ever used StringTokenizer ?

Core Java

Ans. No, Alternatively I have used String.split("\\s") for achieving the same function.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java string stringtokenizer}

Q635. What is ConcurrentLinkedDeque ?

Core Java

Ans. It's a Collections concrete class that provides implementation of a Double Ended queue that allows concurrent insertion, removal, and access operations that can be executed safely across multiple threads.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections queue deque concurrent collections}

Q636. 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

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections list arraylist copyonwritearraylist ConcurrentModificationException Asked in 1 Companies}

Q637. 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.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections list arraylist copyonwritearraylist advantages-disadvantages ConcurrentModificationException Asked in 4 Companies Expert}

Q638. Name few Concurrent Collection Classes ?

Ans. ConcurrentHashMap
ConcurrentLinkedDeque
ConcurrentLinkedQueue
ConcurrentMap
ConcurrentNavigableMap
ConcurrentSkipListMap
ConcurrentSkipListSet

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections concurrent collections}

Q639. Name few Collections Map implementations ?

Ans. AbstractMap
ConcurrentHashMap
ConcurrentSkipListMap
EnumMap
HashMap
IdentityHashMap
LinkedHashMap
SystemFlavorMap
TreeMap
WeakHashMap

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java collections map}

Q640. 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.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java exceptions arrayindexoutofboundexception Asked in 1 Companies}

Search Interview Questions

Help us and Others Improve. Please let us know the questions asked in any of your previous interview.