Java Interview Questions

Set - 1

Java Interview Questions:

1. What is the right data type to represent a price in Java?

Answer: BigDecimal, if memory is not a concern and Performance, is not critical, otherwise double with predefined precision.

2. What is a class in Java?

Answer: Java encapsulates the codes in various classes which define new data types. These new data types are used to create objects.

3. What is a JVM?

Answer: JVM is Java Virtual Machine which is a run time environment for the compiled java class files.

4. Explain method overloading?

Answer: When a Java program contains more than one methods with the same name but different properties, then it is called method overloading.

5. Does Java support multiple inheritances?

Answer: Java doesn’t support multiple inheritances.

6. What restrictions are placed on the location of a package statement within a source code file?

Answer: A package statement must appear as the first line in a source code file (eliminating blank lines and comments).

Read Out: Common Interview Mistakes

7. What is a transient variable?

Answer: A transient variable is a variable that may not be serialized.

8. Is null a keyword?

Answer:

No, the null is not a keyword.

9. What’s new with the stop(), suspend() and resume() methods in JDK 1.2 ?

Answer:

These methods have been deprecated in JDK 1.2.

10. What method is used to specify a container’s layout?

Answer: The setLayout() method is used to specify a container’s layout.

11. What is the immediate superclass of the Applet class?

Answer: The Panel class is the immediate superclass of the Applet class.

12. Can we rethrow the same exception from catch handler?

Answer: Yes, we can rethrow the same exception from our catch handler. If we want to rethrow checked exception

from a catch block we need to declare that exception.

13. what value is a variable of the String type automatically initialized?

Answer: The default value of a String type is null.

14. When a thread blocks on I/O, what state does it enter?

Answer: When it blocks on I/O, A thread enters the waiting state.

15. Which containers use a Flow Layout as their default layout?

Answer: The Panel and Applet classes use the Flow Layout as their default layout.

16. What modifiers may be used with an inner class that is a member of an outer class?

Answer: A (non-local) inner class may be declared as public, protected, private, static, final, or abstract.

17. Which java. util classes and interfaces support event handling?

Answer: The Event Object class and the Event Listener interface support event processing.

18. What is the Vector class?

Answer: The term Vector class provides the ability to implement a growable array of objects.

19. What is the difference between the >> and >>> operators?

Answer: The >> operator carries the sign bit when shifting right while the >>> zero-fills bits that have been shifted out.

20. What is a native method?

Answer: A native method is a method that is applied in a language other than Java.

21. What value does read Line() return when it has reached the end of a file?

Answer:

The readLine() method returns null when it has reached the end of a file.

22. What is clipping?

Answer: Clipping is the process of confining paint operations to a limited area or shape.

23. Can a for statement loop indefinitely?

Answer: Yes, a for statement can loop indefinitely. For example, consider the following: for(;;)

24. Explain Java Coding standards for Methods?

Answer:

1) Method names should start with small letters.

2) Method names are usually verbs

3) If a method contains multiple words, every inner word should start with an uppercase letter.

Ex : toString()

4) Method name must be combination of verb and noun

Ex : getCarName(),getCarNumber()

25. Explain Java Coding Standards for Constants ?

Answer:

Constants in java are created using static and final keywords.

1) Constants contain only uppercase letters.

2) If the constant name is a combination of two words it should be separated by an underscore.

3) Constant names are usually nouns.

Ex:MAX_VALUE, MIN_VALUE, MAX_PRIORITY, MIN_PRIORITY

26. What is synchronization and why is it important?

Answer: The term synchronization is the ability to control the access of multiple threads to shared resources. And it is important because, without it, it is not possible for one thread to modify a shared object while another thread is in the process of using or updating that object’s value. This often leads to major errors.

27. Explain Java Coding Standards for variables?

Answer:

1) Variable names should start with small letters.

2) Variable names should be nouns

3) Short meaningful names are recommended.

4) If there are multiple words every inner world should start with Uppercase character.

Ex : string,value,empName,MEP salary

28. Name three Component subclasses that support painting?

Answer:

The Canvas, Frame, Panel, and Applet classes support painting.

29. What is the difference between JDK and JVM?

Answer: we’re presenting the difference between JDK and JVM in tabular format, take a look…

JDK JVM

Full-Form: Java Development Kit Full Form: Java Virtual Machine

For Development Purpose

To execute the java programs

It provides all the tools, executables and binaries required to compile, debug and execute a Java Program The execution part is handled by JVM to provide machine independence

30. Why Java doesn’t support multiple inheritances?

Answer: Because of “Diamond Problem”, Java doesn’t support multiple inheritances in classes.

31. Why Java is not a pure Object Oriented language?

Answer: Java supports primitive types such as int, byte, short, long, etc that why it is not said to be a pure object-oriented language. 

32. What are the access modifiers?

Answer: Java provides three access controls such as public, private and protected access modifier. When none of these are used, it’s called default access modifier.

33. Can we overload the main method?

Answer:

Yes, we can overload the main method with syntax as public static void main(String args[]).

34. What is the method in java?

Answer: It contains the executable body that can be applied to the specific object of the class.

The method includes method name, parameters or arguments and return type and a body of executable code.

Syntax : type methodName(Argument List){

ex: public float add(int a, int b, int c)

methods can have multiple arguments. Separate with commas when we have multiple arguments.

thrown in the method are instances of their subclass.

35. Can we use catch statement for checked exceptions?

Answer: If there is no chance of raising an exception in our code then we can’t declare catch block for handling

checked exceptions. This raises a compile-time error if we try to handle checked exceptions when there is

no possibility of causing an exception.

36. Explain a situation where finally block will not be executed?

Answer: Finally, the block will not be executed whenever JVM shutdowns. If we use system.exit(0) in try statement

finally block if present will not be executed.

37. Explain about the main() method in java?

Answer: The main () method is the starting point of execution for all java applications.

public static void main(String[] args) {}

String args[] are an array of string objects we need to pass from command line arguments.

Every Java application must have at least one main method. company

38. What is constructor in java?

Answer: A constructor is a special method used to initialize objects in the java.

we use constructors to initialize all variables in the class when an object is created. As and when an object

is created it is initialized automatically with the help of constructor in java.

We have two types of constructors

Default Constructor

Parameterized Constructor

39. How can we find the actual size of an object on the heap?

Answer: In Java, there is no way to find out the actual size of an object on the heap.

40. In how many ways we can do synchronization in java?

Answer:

There are two ways to do synchronization in java:

1) Synchronized methods

2) Synchronized blocks

To do synchronization we use the synchronized keyword.

41. Explain about Automatic type conversion in java?

Answer:

Java automatic type conversion is done if the following conditions are met:

1) When two types are compatible

Ex: int, float

int can be assigned directly to float variable.

2) Destination type is larger than source type.

Ex: int, long. 

Int can be assigned directly to long .Automatic type conversion takes place if int is assigned to long

because long is larger datatype than int.

Widening Conversion comes under Automatic type conversion.

42. In how many ways we can do exception handling in java?

Answer:

We can handle exceptions in either of the two ways :

1) By specifying a try-catch block where we can catch the exception.

2) Declaring a method with throws clause.

43. What does null mean in java?

Answer:

When a reference variable doesn’t point to any value it is assigned null.

Example: Employee employee;

In the above example employee object is not instantiate so it is pointed nowhere. 

44. Can we define a package statement after the import statement in java?

Answer: We can’t define a package statement after the import statement in java. a package statement must be the first

statement in the source file. We can have commented before the package statement.

45. Explain where variables are created in memory?

Answer: When we declare variables are created in the stack. So when the variable is out of scope those

variables get garbage collected.

46. When do we use synchronized blocks and advantages of using synchronized blocks?

Answer: If very few lines of code require synchronization then it is recommended to use synchronized blocks. The

main advantage of synchronized blocks over synchronized methods is it reduces the waiting time of

threads and improves performance of the system.

47. What is the difference between access specifiers and access modifiers in java?

Answer: In C++ we have access specifiers as public, private, protected and default and access modifiers as static,

final. But there is no such division of access specifiers and access modifiers in java. In Java, we have

access to modifiers and nonaccess modifiers.

Access Modifiers: public, private, protected, default

Non Access Modifiers: abstract, final, strip.

48. What access modifiers can be used for class?

Answer: We can use only two access modifiers for class public and default.

public: A class with a public modifier can be visible

1) In the same class

2) In the same package subclass

3) In the same package nonsubclass

4) In the different package subclass

5) In the different package nonsubclass.

default: A class with default modifier can be accessed

1) In the same class

2) In the same package subclass

3) In the same package nonsubclass

4) In the different package subclass

5) In the different package nonsubclass.

49. Explain about abstract classes in java?

Answer: Sometimes we may come across a situation where we cannot provide implementation to all the methods

in a class. We want to leave the implementation to a class that extends it. In such a case, we declare a class

as abstract. To make a class abstract we use keyword abstract. Any class that contains one or more

abstract methods is declared as abstract. If we don’t declare a class as abstract which contains abstract

methods we get a compile-time error. We get the following error.

“The type must be an abstract class to define abstract methods.”

Signature; abstract class

For example, if we take a vehicle class we cannot provide implementation to it because there may be two-wheelers, four-wheelers, etc. At that moment we make vehicle class abstract. All the common features of

vehicles are declared as abstract methods in vehicle class. Any class which extends the vehicle will provide

its method implementation. It’s the responsibility of subclass to provide the implementation.

The important features of abstract classes are :

1) Abstract classes cannot be instantiated.

2) An abstract class contains abstract methods, concrete methods or both.

3) Any class which extends abstract class must override all methods of an abstract class.

4) An abstract class can contain either 0 or more abstract methods.

Though we cannot instantiate abstract classes we can create object references. Through superclass

references, we can point to subclass.

50. Can we create a constructor in abstract class?

Answer: We can create a constructor in the abstract class, it doesn’t give any compilation error. But when we cannot

instantiate class there is no use in creating a constructor for abstract class.

51. What are abstract methods in java?

Answer: An abstract method is a method which doesn’t have anybody. An abstract method is declared with

keyword abstract and semicolon in place of the method body.

Signature : public abstract void ();

Ex : public abstract void get details();

It is the responsibility of subclass to provide implementation to an abstract method defined in the abstract class.

52. State some situations where exceptions may arise in java?

Answer:

1) Accessing an element that does not exist in the array.

2) Invalid conversion of number to string and string to a number.

(NumberFormatException)

3) The invalid casting of class

(Class cast Exception)

4) Trying to create an object for interface or abstract class

(Instantiation Exception)

53. What is an exception in java?

Answer:

In java, an exception is an object. Exceptions are created when abnormal situations arise in our

program. Exceptions can be created by JVM or by our application code. All Exception classes are defined

in java.lang. In other words, we can say Exception as a run time error.

54. What is an error in Java?

Answer: Error is the subclass of Throwable class in java. When errors are caused by our program we call that as

Exception, but some times exceptions are caused due to some environmental issues such as running out of

memory. In such cases, we can’t handle the exceptions. Exceptions which cannot be recovered are called

as errors in java.

Ex: Out of memory issues.

55. What are the advantages of Exception handling in java?

Answer:

1) Separating normal code from exception handling code to avoid abnormal termination of the program.

2) Categorizing into different types of Exceptions so that rather than handling all exceptions with

Exception root class we can handle with specific exceptions. It is recommended to handle exceptions with

specific Exception instead of handling with Exception root class.

3) Call stack mechanism: If a method throws an exception and it is not handled immediately, then that

exception is propagated or thrown to the caller of that method. This propagation continues till it finds an

appropriate exception handler, if it finds handler it would be handled otherwise program terminates

Abruptly.

56. In how many ways we can create threads in java?

Answer:

We can create threads in java by any of the two ways :

1) By extending Thread class

2) By implementing the Runnable interface.

57. Explain creating threads by implementing Runnable class?

Answer: This is the first and foremost way to create threads. By implementing the runnable interface and implementing

the run() method we can create a new thread.

Method signature : public void run()

Run is the starting point for execution for another thread within our program.

Example :

public class MyClass implements Runnable {

@Override

public void run()

58. When do we use synchronized methods in java?

Answer: If multiple threads try to access a method where the method can manipulate the state of the object, in such

a scenario we can declare a method as synchronized.

59. Explain the importance of finally block in java?

Answer: Finally block is used for cleaning up of resources such as closing connections, sockets, etc. if try block

executes with no exceptions then finally is called after try block without executing catch block. If there is

an exception thrown in try block finally block executes immediately after the catch block.

If an exception is thrown, finally block will be executed even if the no catch block handles the exception.

60. Can we catch more than one exception in a single catch block?

Answer: From Java 7, we can catch more than one exception with a single catch block. This type of handling reduces

the code duplication.

Note: When we catch more than one exception in a single catch block, catch parameter is implicitly final.

We cannot assign any value to catch parameter.

Ex : catch(ArrayIndexOutOfBoundsException || ArithmeticException e)