References

new simply creates the object. * To use the object we need a variable to actually refer to it.

Variable refers to instance

The variable has a type and name, only instead of one of the Java's primitive types, the type is a class.

Since this variable "refers" to an object, we call it a reference or reference variable.

reference¶

A variable that can refer to ("point to", "equal") an instance.

The reference allows us to control an instance.

Declaring and Assigning Reference Variables¶

Declaring a reference variable does not create the object. * new creates the object. * We assign the new instance to a reference variable so we can use the object.

Sphere sph;         // Declare reference variable
sph = new Sphere(); // Create new Sphere instance and assign to
                    // reference variable

Many References to One Object¶

We can have two (or more) references point to a single object.

This means both references control the same object.

Sphere sph;               // Declare reference variable
sph = new Sphere();       // Create new Sphere instance and assign to
                             // reference variable
sph.radius = 10.0;

Sphere otherSphereRef = sph; // Now otherSphereRef refers to the object sphRef refers to.

Two references, one object

Drill¶

IntroToObjects/src/drills/SphereReferences.java * Create another reference called otherSphereRef and assign sphRef to it, so that both references refer to the same Sphere object. * Change otherSphereRef's radius. * Output otherSphereRef's radius to the screen. * Output sphRef's radius to the screen. It should have changed.

Prev -- Up -- Next