Clean up code

[jkosternl]

• Simplify code, add final keyword, use diamond operator, correct English, use lambdas, remove .toString, use .isEmpty(), use .addAll, and more
• Thanks to IntelliJ code analyses feature

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 90.90909% with 9 lines in your changes missing coverage. Please review.

Project coverage is 78.14%. Comparing base (48ca3c2) to head (f1c64c9).
Report is 69 commits behind head on master.

Files with missing lines	Patch %	Lines
.../java/com/networknt/schema/utils/JsonNodeUtil.java	50.00%	1 Missing and 1 partial ⚠️
...java/com/networknt/schema/utils/StringChecker.java	0.00%	0 Missing and 2 partials ⚠️
src/main/java/com/networknt/schema/JsonSchema.java	85.71%	0 Missing and 1 partial ⚠️
...n/java/com/networknt/schema/JsonSchemaFactory.java	66.66%	1 Missing ⚠️
...ava/com/networknt/schema/PrefixItemsValidator.java	0.00%	0 Missing and 1 partial ⚠️
...om/networknt/schema/format/IriReferenceFormat.java	0.00%	0 Missing and 1 partial ⚠️
.../main/java/com/networknt/schema/utils/RFC5892.java	94.44%	0 Missing and 1 partial ⚠️

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Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1130      +/-   ##
============================================
- Coverage     78.90%   78.14%   -0.76%     
- Complexity     1965     2061      +96     
============================================
  Files           172      201      +29     
  Lines          6352     6850     +498     
  Branches       1255     1252       -3     
============================================
+ Hits           5012     5353     +341     
- Misses          867     1030     +163     
+ Partials        473      467       -6     

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[stevehu]

It looks like 'sb.append(s, pos, close);' is a syntax for Java 9. We are using Java 11 to build but the output is still Java 8 binary now. Let's see if it works.

[stevehu]

Java 8 can compile the code without any issues. Thanks.