The Object Class
Explore the foundational role of Java's Object class as the root of the inheritance hierarchy. Understand how default methods like toString, equals, and hashCode operate, why overriding them is essential for meaningful data modeling, and how this impacts object comparison and collection usage.
So far, the examples have shown classes defined independently. In Java, every class participates in a common inheritance hierarchy. Every class implicitly extends java.lang.Object, the root of the class hierarchy. As a result, even an empty class inherits the default behavior defined in Object.
By default, these implementations are generic. Objects are represented as a class name followed by a hash code, and equality is based on reference identity rather than object state. To define meaningful domain types, these methods should be overridden to control string representation and equality semantics.
The universal superclass
The Object class sits at the very top of Java’s inheritance tree. When we define a class without using the extends keyword, the Java compiler automatically adds extends Object for us.
If we write:
class EmptyItem { }
The compiler treats it as:
class EmptyItem extends Object { }
This means every reference type in Java:
Inherits methods from
ObjectCan be treated polymorphically as an
ObjectShares a common behavioral baseline
This mechanism ensures that every object in Java shares a common set of methods, allowing generic ...