Latest 60 Java Interview Questions And Answers Pdf

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)

In the above example, e is final we cannot assign any value or modify e in the catch statement.