[IMPALA-7867] Expose collection interfaces, not implementations

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: Impala 3.0
• Component/s: Frontend
• Epic Color: ghx-label-2
• Assignee: Unassigned
• Reporter: Paul Rogers
• Created: 18/Nov/18 22:20
• Updated: 07/Oct/19 03:46
• Resolved: 07/Oct/19 03:46

Description

When using Java collections, a common Java best practice is to expose the collection interface, but hide the implementation choice. This pattern allows us to start with a generic implementation (an ArrayList, say), but evolve to a more specific implementation to achieve certain goals (a LinkedList or ImmutableList, say.)

For whatever reason, the Impala FE code exposes ArrayList, HashMap and other implementation choices as variable types and in method signatures.

This ticket tracks a gradual process of revising the declarations and signatures to use the interfaces List instead of the implementation ArrayList.

Also, the FE code appears to predate Java 7, so that declarations of lists tend to be in one of two forms (with or without Guava):

foo1 = new ArrayList<Bar>();
foo2 = Lists.newArrayList();

Since Java 7, the preferred form is:

foo = new ArrayList<>();