What is the difference between being shallowly and deeply equal? How is this applied to caching?

Question

Found the following in my notes, but I am unable to make sense of it:

Primitive type wrapper classes implement caching for a limited number of value

Answer 1

What you call "shallow equal" is identity: two references (i.e. objects) are identical if they are the very same instances. If you know what pointers are in other languages, you can compare identity to pointer equality.

What you call "deep equal" is equality: two objects a and b are equal if a.equals(b) returns true (and hopefully vice versa). The correctness of equality strongly depends on the way the equals method is implemented. See the Javadoc of the Object class for more details.