Lecture 22: Equivalence and cloning

lecture video

Textbook chapters

3.5-3.6

Equivalence

For a primitive type, testing equivalence between two variables is easy: do they store the same value?

For a reference type, variables hold references to larger data structures. Comparing those references may not be meaningful.

As programmers, we have to decide what equivalence means for objects that we create.

Cloning

For reference types, using the assignment operator = to assign one variable to another just makes both refer to the same underlying object.

Again, as a programmer, we have choices about what cloning means.

• Shallow clone: make a copy, but for reference fields, keep the same references
• Deep clone: make a copy, and copy reference fields into new references

Files used in class

• Movie2.java
• EquivalenceAndCloning.java
• SinglyLinkedList2.java

Additional problems

• Update our implementation for checking equivalence for singly linked lists so that it takes in an Object type instead of a SinglyLinkedList type. (Reference our implementation of equals from Movie.)
• Write both a shallow clone and a deep clone method for SinglyLinkedList.