Which of the following statements are equal for a variable declared in the interface ?

1. int X=10
2. public int X=10
3. public static final int X=10

Java uses sand box security model.

The diamond problem is an ambiguity that can occur when a class multiply inherits from two classes that both descend from a common super class

Array is collection of same data type. Array size is fixed, It cannot be expanded.

But ArrayList is a growable collection of objects.ArrayList is a part of Collections Framework and can work with only objects.

An abstract class is defined with the keyword abstract Eg:
public abstract class MyClass { }

An abstract class is an incomplete class. An abstract class is defined with the keyword abstract . We cannot create an object of the abstract class because it is not complete. It sets a behavioral protocol for all its child classes.

A constructor is a member function of a class that is used to create objects of that class. It has the same name as the class itself, has no return type, and is invoked using the new operator. We cannot invoke a constructor directly.

A method is an ordinary member function of a class. It has its own name, a return type (which may be void), and is invoked using the dot operator.

Variables declared within a method are local variables. Variables declared within the class are member variables.  Variables declared within the class with static modifier are class variables 

It is the ability of an object to behave differently on different situations for the same message.