OOP Principles

abstraction

Data Abstraction is the property by virtue of which only the essential details are displayed to the user. The trivial or the non-essentials units are not displayed to the user. Ex: A phone is viewed as a phone rather than its individual components.
class Phone{
    int name;
    int size;
    int type;
    int country;
}

encapsulation

The internal state of the object must be protected from outside changes and must be performed only by the methods of the object itself.
public class School {
  private secretiveDocs;
  public publicDocs;
}

private secretiveDocs is a parameter that we can use only in this class.  
public publicDocs - this parameter can be used by anyone and  anywhere. 
If we put public instead of private secretiveDocs; then there would be access to this option and anyone could change it. By setting some modifier of access we protect ourselves from the fact that someone can log in and change something there

inheritance

The principle that allows all the heirs of a class to copy its properties, that is to copy the same behavior and have the same properties

class Animal{  
void eat(); 
} 

class Kangaroo extends Animal{  
void drink(); 
}

class Test{  
public static void main(String args[]){  
Kangaroo d=new Kangaroo();  
d.eat();  
d.drink();  
}}  

class Kangaroo to imitate the properties of the Animal class, but the method of "drink" was added

 

polymorphism

Possability to behave with all heirs of  object the same way as if they belong to the class of ancestor

class Machine{  
  void move(){System.out.println("moving");}  
}  
class Bentley extends Bike{  
  void run(){System.out.println("moving safely with 60km");}  
  
  public static void main(String args[]){  
    Machine b = new Bentley();
    b.run();  
  }  
}  

Nothing about abstraction