Most Asked Java Interview Questions

Java is a computer language that focuses on objects. For Android development, it is the most widely used programming language. It may also be used to create desktop apps, online applications, and web services. As a result, we've compiled a list of the most crucial Java Interview Questions that you'll need to obtain your ideal job in the IT sector.

1.What makes Java a platform-agnostic language?

ANS:Because the compiler compiles the code and then converts it to platform-independent byte code that can be run on many platforms, the Java language was designed to be independent of any hardware or software. The sole need for running the byte code is that the machine be equipped with a Java runtime environment (JRE).

2.Why isn't Java a pure object-oriented programming language?

ANS:Java is not a pure object-oriented language because it supports primitive data types such as byte, boolean, char, short, int, float, long, and double.

3.In C/C++, pointers are employed. Why is it that Java doesn't use pointers?

ANS:Beginner programmers should avoid using pointers because they are fairly difficult. The use of pointers can make Java difficult because it focuses on code simplicity. The use of a pointer might also lead to mistakes. Furthermore, when pointers are utilised, security is undermined since pointers allow people to directly access memory. By not including pointers in Java, a certain amount of abstraction is provided. Furthermore, the use of pointers might make garbage collection time-consuming and inaccurate. References are used in Java because, unlike pointers, they cannot be changed.

4.What exactly do you mean when you say "data encapsulation"?

ANS:Data encapsulation is an Object-Oriented Programming concept that involves encapsulating data properties and associated behaviours into a single unit. It aids developers in adhering to modularity when designing software by ensuring that each object is self-contained, with its own methods, characteristics, and functionalities. It is used to protect an object's private properties and so serves the aim of data concealing.

5.Is it possible to overload static methods?

ANS:Yes! In a class, two or more static methods with the same name but different input parameters can exist.

6.Is it possible to override the static methods?

ANS:No! In such cases, static methods with the same signature can be declared in the subclass, but run-time polymorphism is not possible. During runtime, overriding or dynamic polymorphism happens, although static methods are loaded and looked up statically at build time. As a result, these procedures are not overridable.

7.What is the primary goal of waste collection?

ANS:The major goal of this operation is to free up memory space used by superfluous and inaccessible objects during the execution of a Java application by eliminating those objects. This assures that memory is used efficiently, but it does not guarantee that enough memory will be available for programme execution.

8.In the garbage collection process, which component of memory is cleaned: the stack or the heap?

ANS:Heap

9.Overriding static and private methods is allowed in Java. Consider the following statement.

ANS:The assertion is entirely false in this situation. The static methods have no bearing on the objects, therefore they are class-level methods. A static method with a method signature identical to that of the parent class can exist in a child class without causing a compilation fault. Method concealing is the term for the situation described here, and overriding is not feasible. Overriding a private method is impossible because the private method's visibility is limited to the parent class. As a result, only concealing may be made easier, rather than overriding.

10.What distinguishes a HashSet from a TreeSet?

ANS:Despite the fact that both HashSet and TreeSet are not synchronised and assure that no duplicates exist, there are some characteristics that separate a HashSet from a TreeSet. Implementation: The hash table is used to store the elements of a HashSet in an unordered manner. TreeSet, on the other hand, uses a red-black tree to store the items in a sorted order. Complexity/Performance: A HashSet's time amortised complexity for adding, retrieving, and removing elements is O(1). TreeSet has a slightly greater time complexity for performing the same operations, equal to O. (log n). In general, HashSet outperforms TreeSet in terms of performance. HashSet uses the methods hashCode() and equals() to make comparisons between items. TreeSet, on the other hand, uses the compareTo() and compare() methods to make object comparisons easier. HashSet can be used to hold heterogeneous and null items of various types. When introducing heterogeneous objects or null objects into a TreeSet, a runtime exception occurs.

11.When it comes to storing secret data, why is the character array favoured over the string?

ANS:A string in Java is immutable, which means it can't be changed. It remains in the string pool after its declaration as long as it is not eliminated in the form of garbage. In other words, following string value processing, a string remains in the heap region of memory for an undetermined and unregulated time interval.

12.What happens if the static modifier isn't present in the Java main method signature?

ANS:There would be no errors in the compilation. When the programme is launched, however, the JVM is unable to map the main method signature, and the code throws a "NoSuchMethodError" error.

13.What happens if a single Java class contains numerous main methods?

ANS:The programme will not compile because the compiler claims the method has already been declared within the class.

14.What is the process through which an exception propagates through the code?

ANS:When an exception occurs, it looks for the matching catch block first. If the relevant catch block can be found, the block will be executed. Otherwise, the exception propagates up the method call stack until it reaches the caller method, where the process of matching the catch block begins. This process continues until a matching catch block is discovered. The programme is terminated in the main method if the match is not discovered.

15.Is it necessary to follow a try block with a catch block?

ANS:No, the presence of a catch block following a try block is not required. - After a try block, either a catch block or a finally block should be used. If the possibility of exceptions is greater, they should be declared using the method's throws clause.

16.In an array, contiguous memory spaces are often used to store actual values, but not in an ArrayList. Explain.

ANS:Data storage in the form of primitive data types (such as int, float, and so on) is not allowed with ArrayList. The data members/objects in the ArrayList contain references to items that are stored at different locations in memory. As a result, actual objects and non-primitive data types (such as Integer, Double, and so on) are stored in various memory regions.

17.What are the advantages and disadvantages of using an unordered array versus an ordered array?

ANS:The fundamental advantage of having an ordered array is that it has a lower search time complexity of O(log n), whereas an unordered array has a time complexity of O(log n) (n). The ordered array's main disadvantage is its increased insertion time, which is O(n), due to the fact that its elements must be reordered to maintain the array's order after each insertion, whereas the unordered array's time complexity is simply O(1) (1). The proper data structure can be utilised for implementation based on the following two essential factors and the type of scenario a developer demands.

18.Is it feasible in Java to import the same class or package twice, and what happens if you do?

ANS:Although it is possible to import a class or package several times, this is unnecessary because the JVM only loads the package or class once internally.

19.Will it be sufficient to import only the main package if a package has sub packages? e.g. Is it true that importing com.myMainPackage.mySubPackage.* imports com.myMainPackage.mySubPackage.* as well?

ANS:This is a resounding NO. We must recognise that the importing of a package's sub-packages must be done explicitly. When you import the parent package, only the classes within it are imported, not the contents of its child/sub-packages.

20. Will the finally block be executed if the code System.exit(0) is written at the end of try block?

ANS:NO. The control of the program post System.exit(0) is immediately gone and the program gets terminated which is why the finally block never gets executed.

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