What steps are necessary to add three objects of different classes to a data structure of array type?

In Java, arrays are homogeneous data structures, meaning all elements must be of the same type. To add objects of different classes into a single array, you need to use a common base type, such as the Object class.

Example of adding three objects of different classes into an Object array:

Object[] array = new Object[3];
array[0] = "String";          // String
array[1] = 123;               // Integer (autoboxing)
array[2] = new ArrayList<>(); // ArrayList

Thus, an Object array can contain objects of any class, since all classes inherit from Object.