Object

An object is a defined model (or an implementation) of a Class. Every object is created from a class with some common properties (Attributes) . However, certain properties can be unique to a object, and these are known as instance attributes.

An object needs to be instantiated to be stored in a program. As such, an instantiated object is known as an instance.

Instantiation §

To actually store an object in memory, we need to instantiate it. Generally, this is done by declaring it and then using memory allocation to store it.

Java §

//Assume Circle is a class, and Circle(x) creates a circle of x radius
Circle smallCircle = new Circle(30);

This line does multiple steps at once:

1. Creates a Pointer of type Circle
2. Assigns that pointer to a new block of memory which Circle will take up. new is Java’s keyword to let the JVM (Java Virtual Machine) allocate memory

Alternatively, we can do:

Circle smallCircle; //smallCircle points is a null pointer
smallCircle = new Circle(30); //Now assigned

Accessing Methods and Attributes §

In Java, the dot (.) operator is used to access an object’s methods and attributes:

System.out.println(smallCircle.radius) //.radius returns the attribute 'radius'
smallCircle.resize() //.resize() invokes the resize() method

: Be very very careful to make sure an object is first instantiated before trying to access any methods or instance variables.