Java OOP question need help. There are 4 files Boilable.java, Egg.java, OOPLectu

Question

Java OOP question need help. There are 4 files Boilable.java, Egg.java, OOPLecture3.java, and Patato.java. In a new Java project in eclipse with src containing default package with the 4 .javas. I will provide these code and what I need help with is the questions from the OOPLecture3.java file.
import java.util.ArrayList;
public class OOPLecture3 {

    // 2 points
    public static ArrayList<Boilable> Q1(){
        // Return an ArrayList containing 1 Egg and 3 Potatoes

        return null;
    }

    // 2 points
    public static void Q2(ArrayList<Boilable> input){
        // Boil each element in the input list

    }

    // 1 point
    public static String Q3(ArrayList input){
        // Return a single String containing the output of toString() from every element in the input list separated
        // by new line characters ' '
        //
        // Note: This ArrayList does not specify a type. While this is not something you would want to do outside
        //       the classroom, we do it here to show a feature of polymorphism in java. Since the type is not
        //       specified this is not a very useful data structure, but since every class in java extends Object
        //       and ArrayLists must contain objects (recall we can use primitives like int with an ArrayList)
        //       we can assume that this ArrayList contains elements of type Object and we can treat it as an
        //       ArrayList of Objects. As such, we can call the methods associated with the Object class,
        //       including toString().
        return "";
    }
    public static void main(String[] args) {
        // testing
        ArrayList<Boilable> breakfast = Q1();
        System.out.println(Q3(breakfast));
        Q2(breakfast);
        System.out.println(Q3(breakfast));
    }
}
public class Egg implements Boilable{
    private String state;
    public Egg(){
        this.state = "raw";
    }
    @Override
    public void boil(){
        this.state = "hard boiled";
    }
    @Override
    public String toString(){
        return "this egg is " + this.state;
    }
}

public interface Boilable{
    void boil();
}

public class Potato implements Boilable{
    private boolean soft;
    public Potato(){
        this.soft = false;
    }
    @Override
    public void boil(){
        this.soft = true;
    }
    @Override
    public String toString(){
        return this.soft ? "this potato is soft" : "this potato is hard";
    }
}

Explanation / Answer

import java.util.ArrayList;

public class OOPLecture3 {

   // 2 points

   public static ArrayList<Boilable> Q1(){

       // Return an ArrayList containing 1 Egg and 3 Potatoes

       ArrayList<Boilable> list = new ArrayList<>();

       list.add(new Egg());

       list.add(new Potato());

       list.add(new Potato());

       return list;

   }

   // 2 points

   public static void Q2(ArrayList<Boilable> input){

       // Boil each element in the input list

       for(Boilable item : input)

           item.boil();

   }

   // 1 point

   public static String Q3(ArrayList input){

       // Return a single String containing the output of toString() from every element in the input list separated

       // by new line characters ' '

       //

       // Note: This ArrayList does not specify a type. While this is not something you would want to do outside

       // the classroom, we do it here to show a feature of polymorphism in java. Since the type is not

       // specified this is not a very useful data structure, but since every class in java extends Object

       // and ArrayLists must contain objects (recall we can use primitives like int with an ArrayList)

       // we can assume that this ArrayList contains elements of type Object and we can treat it as an

       // ArrayList of Objects. As such, we can call the methods associated with the Object class,

       // including toString().

       String result = "";

       for(Object obj : input)

           result = result + obj.toString()+" ";

       return result;

   }

   public static void main(String[] args) {

       // testing

       ArrayList<Boilable> breakfast = Q1();

       System.out.println(Q3(breakfast));

       Q2(breakfast);

       System.out.println(Q3(breakfast));

   }

}

/*

Sample run:

this egg is raw

this potato is hard

this potato is hard

this egg is hard boiled

this potato is soft

this potato is soft

*/

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