Print Different Object Data From ArrayList in Java

Question

Is there some way to print different data from an ArrayList containing different objects? For example, I created two basic classes:

import java.util.*;

class Furniture{
    String name;
    int weight;

    Furniture(String name, int weight){
        this.name = name;
        this.weight = weight;
    }

    String getName(){
        return name;
    }
    int getWeight(){
        return weight;
    }
    }
}
class Resident{
    String name;

    Resident(String name){
        this.name = name;
    }

    String getName(){
        return name;
    }
}

Then I stored them in an ArrayList<Object> and wanted to print the names, by using declared below printArrayList method:

public class Main{

public static <E> void printArrayList(ArrayList<E> arrayToPrint){
    for(E element : arrayToPrint){
        try{
            System.out.println(element.getName());
        }
        catch(Exception e){
            System.out.println("Exception e: " + e);
        }
    }
}

 public static void main(String []args){
    Furniture sofa = new Furniture("Sofa", 5);
    Resident mike = new Resident("Mike");

    ArrayList<Object> arrayList = new ArrayList<>();

    arrayList.add(sofa);
    arrayList.add(mike);
    printArrayList(arrayList);
}

Now, I know that not all objects can have a variable name or declared get method, therefore I tried to exclude these cases by try/catch. I also tried to exclude it by using fe:

if(elements.getName() == null)

Still, same results.

Answer 1

You don't need to use a parameterized type. Rather introduce a specific interface (for example NameAware) that exposes the getName() method that your classes with implement. In this way you could rely on a common type.

public interface NameAware{
   String getName();
}

public class Resident implements NameAware{
     ...
     public String getName(){
        return name;
    }
}

public class Furniture implements NameAware{
     ...
     public String getName(){
        return name;
    }
}

And define your method as :

public static void printArrayList(ArrayList<NameAware> arrayToPrint) {
    for (NameAware element : arrayToPrint) {
        try {
            System.out.println(element.getName());
        } catch (Exception e) {
            System.out.println("Exception e: " + e);
        }
    }
}

Note that you should change your actual code from :

ArrayList<Object> arrayList = new ArrayList<>();

to

ArrayList<NameAware> arrayList = new ArrayList<>();

Answer 2

The best practice would be to declare an interface with the getName method, and have both Furniture and Resident implement it.

public interface Namable {
    public String getName();
}

Then, use a List<Namable> instead of a List<Object>:

Furniture sofa = new Furniture("Sofa", 5);
Resident mike = new Resident("Mike");

List<Namable> arrayList = new ArrayList<>();

arrayList.add(sofa);
arrayList.add(mike);

for (Namable n : arrayList) {
    System.out.println(n.getName());
}

Answer 3

We can iterate ArrayList by using 1 . Iterator 2. forEach loop 3. For loop

ArrayList arr store object of class User

      ArrayList<User> arr = new ArrayList<User>();

Class User have getter and Setter

     class User{
       private String name;
       private int age;

       public User(String name, int age) {
        super();
        this.name = name;
        this.age = age;
     }

       public String getName() {
          return name;
        }

        public void setName(String name) {
         this.name = name;
        }
        public int getAge() {
         return age;
       }
       public void setAge(int age) {
       this.age = age;
       }

   } 

Now you can get element of list using iterator of User class type

 Iterator<User> itr = arr.iterator();
     while (itr.hasNext()) {
     User user = itr.next();
      System.out.println("Name="+user.getName()+" Age="+user.getAge());
  }

Reference : Java ArrayList Example