Implementing a mixed-type list in Java

I am trying to write a mixed-type list so it can hold integers and strings on the same list.
I have a customType class that can hold one integer and one string.
When I add items to my list, the add function puts elements to the appropriate variable.

public class customType {
    private String str="";
    private int integer=0;
    private String type="";
    private Object NumberFormatException;

    public customType(int integer){
        this.integer=integer;
        type="INTEGER";
    }

    public customType(String str){
        this.str=str;
        type="STRING";
    }
}

Since the parameter type of add function is different, I can overload it.

public class customTypeList {

private ArrayList<customType> elements = new ArrayList<customType>();

.
.
.

public void add(String str){
    elements.add(new customType(str));
    }

public void add(Integer integer){
    elements.add(new customType(integer));
    }
}

But I can not define a get function because the only return type is different and Java is not allowing overload for only different return type functions.

public int get(int i){
    return elements.get(i).getInteger();
    }

public String get(int i){
    return elements.get(i).getStr();
    }

I know, I can use two ArrayLists for this, but I want to implement a mixed-type list like this.
Is there a way to do that?

You could for example create a "raw" list, that is a list that accepts objects of type Object

new ArrayList<Object>();

Then, when you want special handling of Integers or Strings, you'd have to use the instanceof operator to check if the object is an Integer or a String and cast it accordingly.

if(object instanceof Integer) {
  Integer i = (Integer) object;
}

A second approach would be to create different methods for each type of object. I.e.:

public int getInteger(int i);
public String getString(int i);