I really have a problem with the concept of inhert and interface if someone have an idea how i can finally understand it it will be very helpful for me

Question about the task

Under discussion

I'm not getting how interface is working i don't know why he doesn't like User/Loser/Coder/Programmer when i'm using instance of

1. Enter a few strings (keys) from the keyboard [in a loop].
The following strings (keys) are allowed: "user", "loser", "coder", "programmer".
Stop reading in strings after reading in any string that does not match one of the above.

2. For each entered string:
2.1. Create the appropriate object [see Person.java], e.g. create a User object for the string "user".
2.2. Pass this object to the doWork method.

3. Write an implementation of the doWork method, which:
3.1. Calls the live() method on the passed object if person is a User.
3.2. Calls the doNothing() method if person is a Loser.
3.3. Calls the writeCode() method if person is a Coder.
3.4. Calls the enjoy() method if person is a Programmer.

Requirements:

The main method must read strings from the keyboard.
The main method should stop reading strings from the keyboard as soon as the entered string does not match one of the allowed strings ("user", "loser", "coder", "programmer").
For each correctly entered string ("user", "loser", "coder", "programmer"), call the doWork method with the appropriate Person object as the argument.
The Solution class must implement a doWork method with one Person parameter.
The doWork method should call the live() method on the passed object if it is a User.
The doWork method should call the doNothing() method on the passed object if it is a Loser.
The doWork method should call the writeCode() method on the passed object if it is a Coder.
The doWork method should call the enjoy() method on the passed object if it is a Programmer.

package com.codegym.task.task14.task1411; import java.io.BufferedReader; import java.io.InputStreamReader; /* User, loser, coder and programmer */ public class Solution { public static void main(String[] args) throws Exception { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); Person person = null; String key = reader.readLine(); while(reader.read() != -1) { // Create an object. Item 2 doWork(person); // Call doWork } } public static void doWork(Person person) { if(person instanceof User ){ p.live(); }else if(person instanceof Loser){ p.doNothing(); }else if(person instanceof Coder){ p.writeCode(); }else if(person instanceof Programmer){ p.enjoy(); } } }

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Patryk

Level 24 , Warsaw, Poland

14 January 2020, 03:26

Consider interface Person as a box in which we can put things, but as a well-organized people we put in this box only things that have something common with each other (i.e. classes which implements Person interface, because they behave similar, at least should). We can put this thing into a box (Person type variable), still is the same but cannot do whatever it want, is limited to box behaviour (to methods declared in Person interface). In this case Person’s interface doesn’t have any method, so class put into box can’t do anything. We can always take this object back to restore all abilities, but we are doing this blindfolded and we don’t know what is in the box, therefore we need something to check whether it’s a Loser, Coder or sth else, here comes in handy instanceof. We ask instanceof if object we hold is e.g. User or not (instanceof returns true or false). Example:

Loser loser = new Loser();
Person person = loser;
// loser in the box i.e. Person interface, so we can set loser variable to null
loser = null;
// checking whether in person variable is an object which was created from Loser class
if (person instanceof Loser){
// if true assign to variable loser which type is Loser
// and restore access to all methods Loser class
    loser = person;
    loser.doNothing();
// and here we have the same object which we created at the beginning :)
// remember that loser whether is in a box(assign to variable Person type) or not,
// always have access to box abilities(i.e. methods or in case class also variables, which are not private)

John Doe

Level 18 , london, England

11 January 2020, 12:29

package com.codegym.task.task14.task1411;

import java.io.BufferedReader;
import java.io.InputStreamReader;

/*
User, loser, coder and programmer

*/

public class Solution {
    public static void main(String[] args) throws Exception {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        Person person = null;
        String key = reader.readLine();

        while(reader.read() != -1)
        {
            // Create an object. Item 2

            doWork(person); // Call doWork

        }
    }

    public static void doWork(Person person) {
        if(person.equals("user") ){
          person.live();
        }else if(person.equals("Loser")){
            person.doNothing();
        }else if(person.equals("Coder")){
            person.writeCode();
        }else if(person.equals("Programmer")){
            person.enjoy();
        }
    }
}