Java Object

What Does Java Object Mean?

A Java object is a member (also called an instance) of a Java class. Each object has an identity, a behavior and a state.

Techopedia Explains Java Object

Java objects are very similar to the objects we can observe in the real world. A cat, a lighter, a pen, or a car are all objects.

They are characterized by three features:

Identity
State
Behavior

For example, a cat’s state includes its color, size, gender, and age, while its behavior is sleeping, purring, meowing for food, or running around like crazy at 4 AM.

Identity

The identity is a characteristic used to uniquely identify that object – such as a random ID number or an address in memory. Simpler objects like a lighter may have only two states (on and off) and behaviors (turn on, turn off), but they still have an identity (that item’s manufacturing ID, for example).

State

A Java object’s states are stored in fields that represent the individual characteristics of that object. For example, in a first-person shooter video game, a pistol with an eight-bullets clip has nine states in total: one for each bullet (e.g. 8 bullets, 7 bullets, 5 bullets, etc.), plus another one when it’s empty (0 bullets).

Behavior

The object’s behavior is exposed through methods that operate its internal state. For example, the “shooting” behavior will change the state of the pistol from “8 bullets” to “7 bullets” and so forth every time the player shoots with the gun.

The “reloading” behavior will bring back the pistol into the original “8 bullets” state.

There are three steps to creating a Java object:

Declaration of the object.
Instantiation of the object.
Initialization of the object.

When a Java object is declared, a name is associated with that object. The object is instantiated so that memory space can be allocated. Initialization is the process of assigning initial values to the object attribute. Object properties are consistent through all objects from the same class, unlike class properties which are applied only to that specific class.

Properties of Java objects

One can usually interact with an object through its methods. Through states and methods, the objects stay in control of how the world can use it.

For example, any value that is greater than “8 bullets” will be rejected by the method since there’s no state for it. This concept is defined as data encapsulation.

Code can be bundled into individual objects and the source code of every one of them can be written and maintained independently of the others. If a program’s operation is hindered by a particular object, that object can be easily removed and replaced.

A new object t from the class “tree” is created using the following syntax: Tree t = new Tree().