Heap Image

It is useful to draw the heap when thinking about objects and references.

In the example below, we will create a new Sphere3 object and assign it to a reference variable.

Sphere3 sphere;         
sphere = new Sphere3();
sphere.radius = 3.0;

First, we draw the heap and our variable, sphere.

Heap and variable

Next, new creates an object on the heap. The object's field is assigned the default value of 0.0.

Object created

In the same statement, the object's address is assigned to sphere. Represent this by drawing an arrow.

Reference assigned

Finally, this code changes the field radius.

Field changed

Note: we draw the heap's shape to remind us of its name, not because it has some type of shape in memory.

Drill¶

This drill requires pen and paper or whiteboard.
public class Item {
  public double cost;
  
  // methods...
}

Item item1 = new Item();
item1.cost = 3.57;
 
Item item2 = new Item();
item2.cost = 5.00;
* Two Item instances are created and changed. Draw them on the heap. * Item item3 = item2; Add this reference and assignment to your drawing.

(Solution: Objects/com.example.objs.solutions/heapImageSkillDrill.png)

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