[Java] Add accessor methods for data buffers that skip null checking

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Reporter: Wes McKinney / @wesm

Related issues:

• [Java] Remove non-nullable vectors in new vector class hierarchy (relates to)
• [Java] Improving Arrow Vector Reading performance (is related to)
• [Java] Provide light-weight arrow APIs (is related to)

_{Note: This issue was originally created as ARROW-1833. Please see the migration documentation for further details.}

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Jingyuan Wang / @alphalfalfa:
@wesm, could you add some description?

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Wes McKinney / @wesm:
See https://github.com/apache/arrow/blob/master/java/vector/src/main/java/org/apache/arrow/vector/SmallIntVector.java#L125

In some applications, if the null count of a vector is 0, users could use a method like getObjectDirty (not sure what to call it) to get the value from the slot in the ArrowBuf without calling isSet. This would yield better performance for iterating over the values in a vector without nulls, such as one obtained from a Parquet file with a non-nullable (REQUIRED repetition level column)

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Wes McKinney / @wesm:
Does someone want to take a shot at this?

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Jingyuan Wang / @alphalfalfa:
I can take it

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Wes McKinney / @wesm:
Is there still interest in this? Probably also want to start some microbenchmarks so we aren't shooting in the dark on these performance questions

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Wes McKinney / @wesm:
cc @animeshtrivedi

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Micah Kornfield / @emkornfield:
This was addressed differently in #4288 (we've added environment and system properties to turn off the additional check).

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Todd Farmer / @toddfarmer:
Transitioning issue from Resolved to Closed to based on resolution field value.