Core Java - Interview Questions and Answers

55. Why does Java not support operator overloading?

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?

No.

57. What is Externalizable?

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?

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

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

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?

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?

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?

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

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

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?

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?

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?

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