Encapsulation in JAVA

Encapsulation in java means declare instance variables of class as private and access that instance variables using public methods.
Following is the example which shows that Person class having name and age are private instance variables and those are accessed by public getter and setter methods.

public class Person {
    private String name;
    private int age;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
}

OOPs concepts in JAVA

• Abstraction: Hides certain details and only show the essential features of the object.
• Encapsulation: The internal representation of an object is generally hidden from view outside of the object's definition.
• Inheritance: Defines relationships among classes in an object-oriented language.  
• Polymorphism: Define more than one method with the same name.

Difference between abstract class and interface

What is an Abstract Class?

1. An abstract class is a special kind of class that cannot be instantiated.So the question is why we need a class that cannot be instantiated? An abstract class is only to be sub-classed (inherited from). In other words, it only allows other classes to inherit from it but cannot be instantiated. The advantage is that it enforces certain hierarchies for all the subclasses. In simple words, it is a kind of contract that forces all the subclasses to carry on the same hierarchies or standards.
2.  A class may inherit only one abstract class.
3. An abstract class can contain access modifiers for the subs, functions, properties
4. Fast
5. An abstract class can have fields and constants defined

What is an Interface?

1. An interface is not a class. It is an entity that is defined by the word Interface. An interface has no implementation; it only has the signature or in other words, just the definition of the methods without the body. As one of the similarities to Abstract class, it is a contract that is used to define hierarchies for all subclasses or it defines specific set of methods and their arguments. The main difference between them is that a class can implement more than one interface but can only inherit from one abstract class.
2. A class may inherit several interfaces.
3. An interface cannot have access modifiers for the subs, functions, properties etc everything is assumed as public
4. Requires more time to find the actual method in the corresponding classes.
5. No fields can be defined in interfaces

What is difference between Overloading and Overriding?

Overloading: The methods with the same name but it differs by types of arguments and number of arguments.

Overriding:  The methods with the same name and same number of arguments and types but one is in base class and second is in derived class.