Day 7 of 100 - Java: Files scan, OOP concepts

Input scanner

import java.util.Scanner;
//
System.out.println("Enter your name: ");
Scanner scanner = new Scanner(System.in);
String name = scanner.nextLine();
System.out.println("Your name is: " + name);

For scanning files

File file = new File("phone_numbers.txt");
Scanner fileScanner = new Scanner(file);

Reading an ebook text file, project link https://github.com/j143/wordcount-java

Errors

Common runtime errors are formalized into something called Exceptions.

Example, FileNotFoundException.

Use throws keyword.

try {
    openFile("file.txt");
} catch (FileNotFoundException e) {
    // Handle the exception
    System.out.println("File is not available!");
}
// catch(IndexOutOfBoundsException e) {
//
// }
//

Inheritance

Bank account manager

Three different accounts, different account number, balances, limit types

class BankAccount {
  int accountType;
  String accountNumber;
  double balance;
  double limit;
  int transfers;
  Date expiry;
}

in place of the above code

class BankAccount {
  String accountNumber;
  double balance;
}

class COD extends BankAccount {
  Date expiry;
}

Polymorphism

Student student = new Student();
Teacher teacher = new Teacher();
//
// or
Person student = new Student();
Person teacher = new Teacher();

Bag and contents example

public class Bag {
  int currrentWeight;
  boolean canAddItem(Item item);
}

Override

When a class extends a parent class, all public methods declared in the parent class are automatically included in the child class. We are allowed to override any of those methods. Overriding means re-declaring them in the child class and then redefining what they should do.

Super

Re-use the parent method in the child class by using super keyword, followed by a dot and method name.

Interface

Its defines what needs to be done, but now how to do it. Include the methods needed but cannot implement method.

A Class can be inherited by more than one class.

Example, Caravan which is a bus + house

public interface Movable{
  void move(int distance);
  boolean canMove();
}

public interface Habitable {
  boolean canFit(int inhabitants);
}

public class Caravan implements Habitable, Movable {
  void move(int distance) {
    location = location + distance;
  }

  boolean canFit(int inhabitants) {
    return max <= inhabitants;
  }
}