update out-of-date java client examples

[kingkh1995]

Which Issue(s) This PR Fixes

no issue related

Brief Description

1. java client producer examples have some out-of-date comments;
2. add maxPollingSize limit in AsyncSimpleConsumerExample, to avoid "polling full" error.

How Did You Test This Change?

no need to test

[codecov-commenter]

Codecov Report

Merging #627 (8769f0a) into master (19a4afc) will decrease coverage by 8.72%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #627      +/-   ##
============================================
- Coverage     55.84%   47.12%   -8.72%     
- Complexity      664      668       +4     
============================================
  Files           259      207      -52     
  Lines         15580    12109    -3471     
  Branches       3859     3507     -352     
============================================
- Hits           8700     5706    -2994     
+ Misses         6633     6155     -478     
- Partials        247      248       +1     

Flag	Coverage Δ
java	62.97% <ø> (+0.34%)	⬆️
nodejs	?

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see 54 files with indirect coverage changes

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[aaron-ai]

Thanks for you contribution @kingkh1995 . As for the maxPollingSize, it introduces more complexity to our example.

Overall, it looks good.