How to get ArrayList<String> to ArrayList<Object> and vice versa in java?

ArrayList<String> to ArrayList<Object>

Instead of the typed parameter in generics (T) you can also use “?”, representing an unknown type. These are known as wild cards you can use a wild card as − Type of parameter or, a Field or, a Local field. Using wild cards, you can convert ArrayList<String> to ArrayList<Object> as −

ArrayList<String> stringList = (ArrayList<String>)(ArrayList<?>)(list);

Example

import java.util.ArrayList;
import java.util.Iterator;
import java.util.ListIterator;
public class ArrayListExample {
   public static void main(String args[]) {
   
      //Instantiating an ArrayList object
      ArrayList<Object> list = new ArrayList<Object>();
	  
      //populating the ArrayList
      list.add("apples");
      list.add("mangoes");
      list.add("oranges");
	  
      //Converting the Array list of object type into String type
      ArrayList<String> stringList = 
         (ArrayList<String>)(ArrayList<?>)(list);
	  
      //listing the contenmts of the obtained list
      Iterator<String> it = stringList.iterator();
      while(it.hasNext()) {
         System.out.println(it.next());
      }
   }
}

Output

apples
mangoes
oranges

ArrayList<Object> to ArrayList<String>

To convert the ArrayList<Object> to ArrayList<String> −

• Create/Get an ArrayList object of String type.

• Create a new ArrayList object of Object type by passing the above obtained/created object as a parameter to its constructor.

Example

import java.util.ArrayList;
import java.util.Iterator;
import java.util.ListIterator;
public class ArrayListExample {
   public static void main(String args[]) {
   
      //Instantiating an ArrayList object
      ArrayList<String> stringList = new ArrayList<String>();
	  
      //populating the ArrayList
      stringList.add("apples");
      stringList.add("mangoes");
      stringList.add("oranges");
	  
      //Converting the Array list of String type to object type
      ArrayList<Object> objectList = new ArrayList<Object>(stringList);
	  
      //listing the contents of the obtained list
      Iterator<String> it = stringList.iterator();
      while(it.hasNext()) {
         System.out.println(it.next());
      }
   }
}

Output

apples
mangoes
oranges