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Janardhan Pulivarthi
Janardhan Pulivarthi

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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);
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For scanning files

File file = new File("phone_numbers.txt"); Scanner fileScanner = new Scanner(file);
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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) { // // } //
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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; }
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in place of the above code

class BankAccount { String accountNumber; double balance; } class COD extends BankAccount { Date expiry; }
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Polymorphism 

Student student = new Student(); Teacher teacher = new Teacher(); // // or Person student = new Student(); Person teacher = new Teacher();
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Bag and contents example

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