20+ Starwalk Services Interview Questions and Answers

Java certification is not mandatory for a Java Developer role.

• Certification is not a measure of practical skills and experience.

• Experience and skills are more important than certification.

• Certification can be helpful in some cases, but not mandatory.

• Certification can be expensive and time-consuming.

• Employers may value certification differently.

• Examples of Java certifications: Oracle Certified Professional Java SE 11 Developer, Java SE 8 Programmer, etc.

Memory is allocated when an instance of a class is created.

• Memory allocation happens when an object is created using the 'new' keyword.

• Static variables are allocated memory when the class is loaded.

• Memory is released when the object is no longer referenced or when the program terminates.

We can use composition, aggregation, or association to connect two classes.

• Composition is a strong form of aggregation where the lifetime of the contained object is controlled by the container object.

• Aggregation is a weaker form of composition where the contained object has an independent lifecycle.

• Association is a relationship between two classes where one class uses the functionality of another class.

• Examples of association are dependency, inheritance, and realization.

• Examp...read more

Access modifiers in Java are used to set the accessibility of classes, methods, and variables.

• There are four types of access modifiers in Java: public, private, protected, and default.

• Public: accessible from anywhere in the program.

• Private: accessible only within the same class.

• Protected: accessible within the same class, same package, and subclasses.

• Default: accessible within the same package only.

Abstract class can have implementation while interface cannot. A class can implement multiple interfaces but can only extend one abstract class.

• Abstract class can have constructors while interface cannot.

• Abstract class can have instance variables while interface cannot.

• Abstract class can have non-abstract methods while interface can only have abstract methods.

• A class can implement multiple interfaces but can only extend one abstract class.

• Abstract classes are used when there ...read more

Composition is a way to combine objects to create complex structures, while inheritance is a way to create new classes based on existing ones.

• Composition is a 'has-a' relationship, where an object contains other objects as its parts.

• Inheritance is an 'is-a' relationship, where a subclass inherits properties and behaviors from its superclass.

• Composition allows for greater flexibility and modularity in design, as objects can be easily swapped out or added.

• Inheritance can lead t...read more

Collections are used to store and manipulate groups of objects in Java. There are three main types of collections.

• The three main types of collections are List, Set, and Map.

• List is an ordered collection that allows duplicates. Example: ArrayList.

• Set is an unordered collection that does not allow duplicates. Example: HashSet.

• Map is a collection that maps keys to values and does not allow duplicate keys. Example: HashMap.

throw is used to explicitly throw an exception while throws is used to declare an exception that a method may throw.

• throw is used within a method to throw an exception when a certain condition is met

• throws is used in the method signature to declare the exceptions that the method may throw

• throw is followed by an instance of an exception class while throws is followed by the name of the exception class

• throw is used to handle exceptions within a method while throws is used to pr...read more

No, subclass cannot inherit properties of parent class if parent class is not loaded.

• In order for a subclass to inherit properties of a parent class, the parent class must be loaded.

• If the parent class is not loaded, the subclass will not have access to its properties.

• This is because inheritance is a compile-time concept and requires the parent class to be present during compilation.

• Attempting to access properties of an unloaded parent class will result in a compilation error...read more

No, subclass cannot access private methods of parent class.

• Private methods are only accessible within the same class where they are defined.

• Subclasses can access protected and public methods of parent class.

• Private methods can be accessed indirectly through public or protected methods of parent class.

A stack is a data structure that follows the Last In First Out (LIFO) principle.

• Elements are added and removed from the top of the stack.

• Push() adds an element to the top of the stack.

• Pop() removes the top element from the stack.

• Peek() returns the top element without removing it.

• Used in programming for function calls, expression evaluation, and memory management.

A queue is a data structure that follows the FIFO (First In First Out) principle.

• Elements are added to the back of the queue and removed from the front.

• Common operations include enqueue (add to back) and dequeue (remove from front).

• Examples include a line of people waiting for a movie or a printer queue.

• Java provides the Queue interface and its implementations like LinkedList and PriorityQueue.

Polymorphism is when an object can take on multiple forms and behave differently based on the context.

• A car can be a vehicle, but it can also be a sports car or a family car, each with different behaviors.

• A shape can be a square, rectangle, or triangle, each with different methods for calculating area and perimeter.

• A media player can play different types of media, such as audio or video, each with different playback controls.

Yes, Java supports multi level inheritance.

• Multi level inheritance is the process of inheriting a class from another derived class.

• It helps in creating a hierarchy of classes with each level inheriting properties from the previous level.

• For example, class C can inherit from class B, which in turn inherits from class A.

• Java does not support multiple inheritance, where a class can inherit from multiple classes at the same level.

Errors are unrecoverable, while exceptions are recoverable.

• Errors are caused by the environment in which the application is running, while exceptions are caused by the application itself.

• Errors cannot be handled by the application, while exceptions can be handled using try-catch blocks.

• Examples of errors include OutOfMemoryError and StackOverflowError, while examples of exceptions include NullPointerException and ArrayIndexOutOfBoundsException.

The four pillars of OOPS are Abstraction, Encapsulation, Inheritance, and Polymorphism.

• Abstraction: Hiding implementation details and showing only necessary information.

• Encapsulation: Binding data and methods together to protect data from outside interference.

• Inheritance: Creating new classes from existing ones, inheriting properties and methods.

• Polymorphism: Ability of objects to take on multiple forms or behaviors.

Arrays are fixed in size and stored in stack memory, while heap is dynamic and stored in heap memory.

• Arrays are declared with a fixed size, while heap can grow or shrink dynamically.

• Arrays are stored in stack memory, while heap is stored in heap memory.

• Arrays can only store elements of the same data type, while heap can store objects of different types.

• Examples of arrays include int[], char[], and String[], while examples of heap objects include ArrayList, HashMap, and Linked...read more

No, Set does not allow duplicates.

• Set is a collection that does not allow duplicates.

• If you try to add a duplicate element to a Set, it will not be added.

• You can use a List if you need to allow duplicates.

Yes, duplicates can be added to an array.

• Arrays in Java can contain duplicate elements.

• Duplicate elements can be added to an array using the add() method of ArrayList class.

• For example, int[] arr = {1, 2, 3, 3, 4}; or ArrayList list = new ArrayList<>(Arrays.asList(1, 2, 3, 3, 4));

protected is a Java access modifier that allows access within the same package and subclasses.

• Protected members can be accessed within the same package and subclasses.

• It is used to provide encapsulation and prevent direct access from outside the class.

• Protected members can be accessed using the dot operator.

• Example: protected int num; can be accessed in a subclass using obj.num;

Collections are objects that group multiple elements into a single unit.

• Collections are used to store, retrieve, manipulate and communicate aggregate data.

• Java provides a set of interfaces and classes that implement various types of collections.

• Examples of collections include List, Set, Map, Queue, etc.

• Collections can be used to improve code readability, reusability, and performance.

Yes, we can have multiple try blocks in Java.

• Multiple try blocks can be used to handle different exceptions separately.

• Each try block must have at least one catch or finally block.

• Nested try blocks can also be used.

• Example: try { //code } catch (Exception e) { //code } try { //code } catch (IOException e) { //code }

• Example of nested try blocks: try { try { //code } catch (Exception e) { //code } } catch (Exception e) { //code }

Exception handling is the process of handling errors and exceptions that occur during program execution.

• Exceptions are objects that represent errors or exceptional situations that occur during program execution.

• Exception handling involves catching and handling these exceptions to prevent program crashes.

• Java provides try-catch-finally blocks for handling exceptions.

• Examples of exceptions include NullPointerException, ArrayIndexOutOfBoundsException, and FileNotFoundException.