Object

Ultimately, every class in Java descends from java.lang.Object.

This means all classes inherit several Object methods. * public boolean equals(Object obj) - value comparison. * public String toString() — return a String representing details about this object. * public final Class getClass() — retrieve a Class object. * public int hashCode() — retrieve a numeric identifier for this object.

Every Class IS-A Object

If we don't declare that a class extends another class, it implicitly extends Object.

public class Person {
  // ...
  public Person() {

  }
  // ...
}

The Person class has no extends directive, so it extends Object. * Its constructor's implicit call to super() is Object's no-arg constructor.

Therefore, Employee and DataAnalyst also have Object in their hierarchy, and inherit Object methods.

Class Hierarchies and Memory

When instantiating a subclass, only one object is built in memory. * The new object contains memory allocations for all of the fields in the subclass, as well as those in the superclass. * You will not have a separate object created for the subclass and the superclass.

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