100+ Important Core Java Interview Questions and Answers 51 to 70

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Core Java Interview Questions and Answers: Question 51 to Question 70

Here you can find the 100+ most frequently asked important core java interview questions and answers (51 to 70) for placement (campus) interview and competitive examinations.

51. Can a class be defined inside an Interface?

Answer: Yes it’s possible.

52. Can an Interface be defined inside a class?

Answer: Yes it’s possible.

53. What is a Marker Interface?

Answer: An Interface which doesn’t have any declaration inside but still enforces a mechanism.

54. Which object oriented Concept is achieved by using overloading and overriding?

Answer: Polymorphism.

55. Why does Java not support operator overloading?

Answer: Operator overloading makes the code very difficult to read and maintain. To maintain code simplicity, Java doesn’t support operator overloading.

56. Can we define private and protected modifiers for variables in interfaces?

Answer: No.

57. What is Externalizable?

Answer: Externalizable is an Interface that extends Serializable Interface. And sends data into Streams in Compressed Format. It has two methods, writeExternal(ObjectOuput out) and readExternal(ObjectInput in)

58. What modifiers are allowed for methods in an Interface?

Answer: Only public and abstract modifiers are allowed for methods in interfaces.

59. What is a local, member and a class variable?

Answer: Variables declared within a method are “local” variables. Variables declared within the class i.e not within any methods are “member” variables (global variables).

Variables declared within the class i.e not within any methods and are defined as “static” are class variables.

60. What is an abstract method?

Answer: An abstract method is a method whose implementation is deferred to a subclass.

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

Answer: The read() method returns -1 when it has reached the end of a file.

62. Can a Byte object be cast to a double value?

Answer: No, an object cannot be cast to a primitive value.

63. What is the difference between a static and a non-static inner class?

Answer: A non-static inner class may have object instances that are associated with instances of the class’s outer class. A static inner class does not have any object instances.

64. What is an object’s lock and which object’s have locks?

Answer: An object’s lock is a mechanism that is used by multiple threads to obtain synchronized access to the object. A thread may execute a synchronized method of an object only after it has acquired the object’s lock. All objects and classes have locks. A class’s lock is acquired on the class’s Class object.

65. What is the % operator?

Answer: It is referred to as the modulo or remainder operator. It returns the remainder of dividing the first operand by the second operand.

66. When can an object reference be cast to an interface reference?

Answer: An object reference be cast to an interface reference when the object implements the referenced interface.

67. Which class is extended by all other classes?

Answer: The Object class is extended by all other classes.

68. Which non-Unicode letter characters may be used as the first character of an identifier?

Answer: The non-Unicode letter characters $ and _ may appear as the first character of an identifier

69. What restrictions are placed on method overloading?

Answer: Two methods may not have the same name and argument list but different return types.

70. What is casting?

Answer: There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference.


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