diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index b63e826..351e300 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -5,16 +5,16 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: ['2.5', '2.6', '2.7', '3.0', 'head', 'jruby-9.2.10.0']
+        ruby: ['3.0', '3.1', '3.2', '3.3', 'head', 'jruby-9.4.5.0']
         gemfile: ['1.14.0', '1.15.0', '1.16.1', '1.17.0', '1.18.4', '1.19.1']
     runs-on: ubuntu-latest
     continue-on-error: ${{ matrix.ruby == 'head' }}
     env:
       BUNDLE_GEMFILE: ${{ github.workspace }}/gemfiles/rubocop_${{ matrix.gemfile }}.gemfile
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - uses: ruby/setup-ruby@v1
       with:
         ruby-version: ${{ matrix.ruby }}
         bundler-cache: true
-    - run: bundle exec rspec spec
\ No newline at end of file
+    - run: bundle exec rspec spec
diff --git a/.rubocop.yml b/.rubocop.yml
index 3a36849..6640ebf 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -2,12 +2,3 @@ inherit_from: .rubocop_todo.yml
 
 AllCops:
   DisplayCopNames: true
-  TargetRubyVersion: 2.2
-
-Style/FrozenStringLiteralComment:
-  SupportedStyles:
-    - when_needed
-
-Style/FileName:
-  Exclude:
-    - Appraisals
diff --git a/.rubocop_todo.yml b/.rubocop_todo.yml
index 8ec7736..d9d16f1 100644
--- a/.rubocop_todo.yml
+++ b/.rubocop_todo.yml
@@ -1,24 +1,120 @@
+# This configuration was generated by
+# `rubocop --auto-gen-config`
+# on 2024-01-21 08:48:58 UTC using RuboCop version 1.60.1.
+# The point is for the user to remove these configuration records
+# one by one as the offenses are removed from the code base.
+# Note that changes in the inspected code, or installation of new
+# versions of RuboCop, may require this file to be generated again.
+
 # Offense count: 1
-# Configuration parameters: CountComments, ExcludedMethods.
-Metrics/BlockLength:
-  Max: 42
+# Configuration parameters: Severity, Include.
+# Include: **/*.gemspec
+Gemspec/RequiredRubyVersion:
+  Exclude:
+    - 'rubocop-checkstyle_formatter.gemspec'
 
-# Offense count: 9
-# Configuration parameters: AllowHeredoc, AllowURI, URISchemes, IgnoreCopDirectives, IgnoredPatterns.
-# URISchemes: http, https
-Metrics/LineLength:
-  Max: 111
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+Layout/EmptyLineAfterMagicComment:
+  Exclude:
+    - 'lib/rubocop/formatter/checkstyle_formatter.rb'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: final_newline, final_blank_line
+Layout/TrailingEmptyLines:
+  Exclude:
+    - 'Gemfile'
 
 # Offense count: 1
-# Cop supports --auto-correct.
-# Configuration parameters: Keywords.
-# Keywords: TODO, FIXME, OPTIMIZE, HACK, REVIEW
+# Configuration parameters: CountComments, CountAsOne, AllowedMethods, AllowedPatterns.
+# AllowedMethods: refine
+Metrics/BlockLength:
+  Max: 52
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: Keywords, RequireColon.
+# Keywords: TODO, FIXME, OPTIMIZE, HACK, REVIEW, NOTE
 Style/CommentAnnotation:
   Exclude:
     - 'lib/rubocop/formatter/checkstyle_formatter.rb'
 
 # Offense count: 2
-# Cop supports --auto-correct.
-Style/CommentIndentation:
+# This cop supports safe autocorrection (--autocorrect).
+Style/Encoding:
+  Exclude:
+    - 'Rakefile'
+    - 'lib/rubocop/formatter/checkstyle_formatter.rb'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+Style/ExpandPathArguments:
+  Exclude:
+    - 'rubocop-checkstyle_formatter.gemspec'
+
+# Offense count: 10
+# This cop supports unsafe autocorrection (--autocorrect-all).
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: always, always_true, never
+Style/FrozenStringLiteralComment:
   Exclude:
+    - 'Gemfile'
+    - 'Rakefile'
+    - 'gemfiles/rubocop_1.20.0.gemfile'
+    - 'gemfiles/rubocop_1.25.1.gemfile'
+    - 'gemfiles/rubocop_1.30.1.gemfile'
+    - 'gemfiles/rubocop_1.35.1.gemfile'
+    - 'gemfiles/rubocop_1.40.0.gemfile'
+    - 'gemfiles/rubocop_1.45.1.gemfile'
+    - 'gemfiles/rubocop_1.50.2.gemfile'
     - 'lib/rubocop/formatter/checkstyle_formatter.rb'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+Style/IfUnlessModifier:
+  Exclude:
+    - 'spec/rubocop/formatter/checkstyle_formatter_spec.rb'
+
+# Offense count: 1
+# This cop supports unsafe autocorrection (--autocorrect-all).
+# Configuration parameters: EnforcedStyle.
+# SupportedStyles: short, verbose
+Style/PreferredHashMethods:
+  Exclude:
+    - 'lib/rubocop/formatter/checkstyle_formatter.rb'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+Style/StderrPuts:
+  Exclude:
+    - 'Rakefile'
+
+# Offense count: 1
+# This cop supports unsafe autocorrection (--autocorrect-all).
+# Configuration parameters: Mode.
+Style/StringConcatenation:
+  Exclude:
+    - 'lib/rubocop/formatter/checkstyle_formatter.rb'
+
+# Offense count: 28
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: EnforcedStyle, ConsistentQuotesInMultiline.
+# SupportedStyles: single_quotes, double_quotes
+Style/StringLiterals:
+  Exclude:
+    - 'gemfiles/rubocop_1.20.0.gemfile'
+    - 'gemfiles/rubocop_1.25.1.gemfile'
+    - 'gemfiles/rubocop_1.30.1.gemfile'
+    - 'gemfiles/rubocop_1.35.1.gemfile'
+    - 'gemfiles/rubocop_1.40.0.gemfile'
+    - 'gemfiles/rubocop_1.45.1.gemfile'
+    - 'gemfiles/rubocop_1.50.2.gemfile'
+
+# Offense count: 1
+# This cop supports safe autocorrection (--autocorrect).
+# Configuration parameters: AllowHeredoc, AllowURI, URISchemes, IgnoreCopDirectives, AllowedPatterns.
+# URISchemes: http, https
+Layout/LineLength:
+  Max: 136
diff --git a/Appraisals b/Appraisals
index 86e4b64..882c119 100644
--- a/Appraisals
+++ b/Appraisals
@@ -1,10 +1,13 @@
+# frozen_string_literal: true
+
 [
-  '1.14.0',
-  '1.15.0',
-  '1.16.1',
-  '1.17.0',
-  '1.18.4',
-  '1.19.1'
+  '1.20.0',
+  '1.25.1',
+  '1.30.1',
+  '1.35.1',
+  '1.40.0',
+  '1.45.1',
+  '1.50.2'
 ].each do |version|
   appraise "rubocop-#{version}" do
     gem 'rubocop', version
diff --git a/gemfiles/rubocop_1.18.4.gemfile b/gemfiles/rubocop_1.18.4.gemfile
deleted file mode 100644
index 2cdd6e2..0000000
--- a/gemfiles/rubocop_1.18.4.gemfile
+++ /dev/null
@@ -1,7 +0,0 @@
-# This file was generated by Appraisal
-
-source "https://rubygems.org"
-
-gem "rubocop", "1.18.4"
-
-gemspec path: "../"
diff --git a/gemfiles/rubocop_1.18.4.gemfile.lock b/gemfiles/rubocop_1.18.4.gemfile.lock
deleted file mode 100644
index 74a11d7..0000000
--- a/gemfiles/rubocop_1.18.4.gemfile.lock
+++ /dev/null
@@ -1,64 +0,0 @@
-PATH
-  remote: ..
-  specs:
-    rubocop-checkstyle_formatter (0.5.0)
-      rubocop (>= 1.14.0)
-
-GEM
-  remote: https://rubygems.org/
-  specs:
-    appraisal (2.4.1)
-      bundler
-      rake
-      thor (>= 0.14.0)
-    ast (2.4.2)
-    diff-lcs (1.4.4)
-    parallel (1.20.1)
-    parser (3.0.2.0)
-      ast (~> 2.4.1)
-    rainbow (3.0.0)
-    rake (13.0.6)
-    regexp_parser (2.1.1)
-    rexml (3.2.5)
-    rspec (3.5.0)
-      rspec-core (~> 3.5.0)
-      rspec-expectations (~> 3.5.0)
-      rspec-mocks (~> 3.5.0)
-    rspec-core (3.5.4)
-      rspec-support (~> 3.5.0)
-    rspec-expectations (3.5.0)
-      diff-lcs (>= 1.2.0, < 2.0)
-      rspec-support (~> 3.5.0)
-    rspec-mocks (3.5.0)
-      diff-lcs (>= 1.2.0, < 2.0)
-      rspec-support (~> 3.5.0)
-    rspec-support (3.5.0)
-    rubocop (1.18.4)
-      parallel (~> 1.10)
-      parser (>= 3.0.0.0)
-      rainbow (>= 2.2.2, < 4.0)
-      regexp_parser (>= 1.8, < 3.0)
-      rexml
-      rubocop-ast (>= 1.8.0, < 2.0)
-      ruby-progressbar (~> 1.7)
-      unicode-display_width (>= 1.4.0, < 3.0)
-    rubocop-ast (1.10.0)
-      parser (>= 3.0.1.1)
-    ruby-progressbar (1.11.0)
-    thor (1.1.0)
-    unicode-display_width (2.0.0)
-
-PLATFORMS
-  java
-  ruby
-
-DEPENDENCIES
-  appraisal (~> 2.4.1)
-  bundler (>= 2.2.10)
-  rake (>= 12.3.3)
-  rspec (~> 3.5.0)
-  rubocop (= 1.18.4)
-  rubocop-checkstyle_formatter!
-
-BUNDLED WITH
-   2.2.25
diff --git a/gemfiles/rubocop_1.19.1.gemfile b/gemfiles/rubocop_1.19.1.gemfile
deleted file mode 100644
index e7113ee..0000000
--- a/gemfiles/rubocop_1.19.1.gemfile
+++ /dev/null
@@ -1,7 +0,0 @@
-# This file was generated by Appraisal
-
-source "https://rubygems.org"
-
-gem "rubocop", "1.19.1"
-
-gemspec path: "../"
diff --git a/gemfiles/rubocop_1.14.0.gemfile b/gemfiles/rubocop_1.20.0.gemfile
similarity index 79%
rename from gemfiles/rubocop_1.14.0.gemfile
rename to gemfiles/rubocop_1.20.0.gemfile
index 412732b..34861ac 100644
--- a/gemfiles/rubocop_1.14.0.gemfile
+++ b/gemfiles/rubocop_1.20.0.gemfile
@@ -2,6 +2,6 @@
 
 source "https://rubygems.org"
 
-gem "rubocop", "1.14.0"
+gem "rubocop", "1.20.0"
 
 gemspec path: "../"
diff --git a/gemfiles/rubocop_1.19.1.gemfile.lock b/gemfiles/rubocop_1.20.0.gemfile.lock
similarity index 71%
rename from gemfiles/rubocop_1.19.1.gemfile.lock
rename to gemfiles/rubocop_1.20.0.gemfile.lock
index fe2fe27..42c693c 100644
--- a/gemfiles/rubocop_1.19.1.gemfile.lock
+++ b/gemfiles/rubocop_1.20.0.gemfile.lock
@@ -2,7 +2,7 @@ PATH
   remote: ..
   specs:
     rubocop-checkstyle_formatter (0.5.0)
-      rubocop (>= 1.14.0)
+      rubocop (>= 1.20.0)
 
 GEM
   remote: https://rubygems.org/
@@ -12,14 +12,16 @@ GEM
       rake
       thor (>= 0.14.0)
     ast (2.4.2)
-    diff-lcs (1.4.4)
-    parallel (1.20.1)
-    parser (3.0.2.0)
+    diff-lcs (1.5.0)
+    parallel (1.24.0)
+    parser (3.3.0.4)
       ast (~> 2.4.1)
-    rainbow (3.0.0)
-    rake (13.0.6)
-    regexp_parser (2.1.1)
-    rexml (3.2.5)
+      racc
+    racc (1.7.3)
+    rainbow (3.1.1)
+    rake (13.1.0)
+    regexp_parser (2.9.0)
+    rexml (3.2.6)
     rspec (3.5.0)
       rspec-core (~> 3.5.0)
       rspec-expectations (~> 3.5.0)
@@ -33,7 +35,7 @@ GEM
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.5.0)
     rspec-support (3.5.0)
-    rubocop (1.19.1)
+    rubocop (1.20.0)
       parallel (~> 1.10)
       parser (>= 3.0.0.0)
       rainbow (>= 2.2.2, < 4.0)
@@ -42,23 +44,23 @@ GEM
       rubocop-ast (>= 1.9.1, < 2.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 1.4.0, < 3.0)
-    rubocop-ast (1.10.0)
-      parser (>= 3.0.1.1)
-    ruby-progressbar (1.11.0)
-    thor (1.1.0)
-    unicode-display_width (2.0.0)
+    rubocop-ast (1.30.0)
+      parser (>= 3.2.1.0)
+    ruby-progressbar (1.13.0)
+    thor (1.3.0)
+    unicode-display_width (2.5.0)
 
 PLATFORMS
-  java
   ruby
+  x86_64-darwin-22
 
 DEPENDENCIES
   appraisal (~> 2.4.1)
   bundler (>= 2.2.10)
   rake (>= 12.3.3)
   rspec (~> 3.5.0)
-  rubocop (= 1.19.1)
+  rubocop (= 1.20.0)
   rubocop-checkstyle_formatter!
 
 BUNDLED WITH
-   2.2.25
+   2.5.5
diff --git a/gemfiles/rubocop_1.16.1.gemfile b/gemfiles/rubocop_1.25.1.gemfile
similarity index 79%
rename from gemfiles/rubocop_1.16.1.gemfile
rename to gemfiles/rubocop_1.25.1.gemfile
index 618da2d..958bc75 100644
--- a/gemfiles/rubocop_1.16.1.gemfile
+++ b/gemfiles/rubocop_1.25.1.gemfile
@@ -2,6 +2,6 @@
 
 source "https://rubygems.org"
 
-gem "rubocop", "1.16.1"
+gem "rubocop", "1.25.1"
 
 gemspec path: "../"
diff --git a/gemfiles/rubocop_1.16.1.gemfile.lock b/gemfiles/rubocop_1.25.1.gemfile.lock
similarity index 66%
rename from gemfiles/rubocop_1.16.1.gemfile.lock
rename to gemfiles/rubocop_1.25.1.gemfile.lock
index e169bf9..377da8b 100644
--- a/gemfiles/rubocop_1.16.1.gemfile.lock
+++ b/gemfiles/rubocop_1.25.1.gemfile.lock
@@ -2,7 +2,7 @@ PATH
   remote: ..
   specs:
     rubocop-checkstyle_formatter (0.5.0)
-      rubocop (>= 1.14.0)
+      rubocop (>= 1.20.0)
 
 GEM
   remote: https://rubygems.org/
@@ -12,14 +12,16 @@ GEM
       rake
       thor (>= 0.14.0)
     ast (2.4.2)
-    diff-lcs (1.4.4)
-    parallel (1.20.1)
-    parser (3.0.2.0)
+    diff-lcs (1.5.0)
+    parallel (1.24.0)
+    parser (3.3.0.4)
       ast (~> 2.4.1)
-    rainbow (3.0.0)
-    rake (13.0.6)
-    regexp_parser (2.1.1)
-    rexml (3.2.5)
+      racc
+    racc (1.7.3)
+    rainbow (3.1.1)
+    rake (13.1.0)
+    regexp_parser (2.9.0)
+    rexml (3.2.6)
     rspec (3.5.0)
       rspec-core (~> 3.5.0)
       rspec-expectations (~> 3.5.0)
@@ -33,32 +35,32 @@ GEM
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.5.0)
     rspec-support (3.5.0)
-    rubocop (1.16.1)
+    rubocop (1.25.1)
       parallel (~> 1.10)
-      parser (>= 3.0.0.0)
+      parser (>= 3.1.0.0)
       rainbow (>= 2.2.2, < 4.0)
       regexp_parser (>= 1.8, < 3.0)
       rexml
-      rubocop-ast (>= 1.7.0, < 2.0)
+      rubocop-ast (>= 1.15.1, < 2.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 1.4.0, < 3.0)
-    rubocop-ast (1.10.0)
-      parser (>= 3.0.1.1)
-    ruby-progressbar (1.11.0)
-    thor (1.1.0)
-    unicode-display_width (2.0.0)
+    rubocop-ast (1.30.0)
+      parser (>= 3.2.1.0)
+    ruby-progressbar (1.13.0)
+    thor (1.3.0)
+    unicode-display_width (2.5.0)
 
 PLATFORMS
-  java
   ruby
+  x86_64-darwin-22
 
 DEPENDENCIES
   appraisal (~> 2.4.1)
   bundler (>= 2.2.10)
   rake (>= 12.3.3)
   rspec (~> 3.5.0)
-  rubocop (= 1.16.1)
+  rubocop (= 1.25.1)
   rubocop-checkstyle_formatter!
 
 BUNDLED WITH
-   2.2.25
+   2.5.5
diff --git a/gemfiles/rubocop_1.15.0.gemfile b/gemfiles/rubocop_1.30.1.gemfile
similarity index 79%
rename from gemfiles/rubocop_1.15.0.gemfile
rename to gemfiles/rubocop_1.30.1.gemfile
index 5b181ed..6892030 100644
--- a/gemfiles/rubocop_1.15.0.gemfile
+++ b/gemfiles/rubocop_1.30.1.gemfile
@@ -2,6 +2,6 @@
 
 source "https://rubygems.org"
 
-gem "rubocop", "1.15.0"
+gem "rubocop", "1.30.1"
 
 gemspec path: "../"
diff --git a/gemfiles/rubocop_1.14.0.gemfile.lock b/gemfiles/rubocop_1.30.1.gemfile.lock
similarity index 65%
rename from gemfiles/rubocop_1.14.0.gemfile.lock
rename to gemfiles/rubocop_1.30.1.gemfile.lock
index 412ec1f..5391cd9 100644
--- a/gemfiles/rubocop_1.14.0.gemfile.lock
+++ b/gemfiles/rubocop_1.30.1.gemfile.lock
@@ -2,7 +2,7 @@ PATH
   remote: ..
   specs:
     rubocop-checkstyle_formatter (0.5.0)
-      rubocop (>= 1.14.0)
+      rubocop (>= 1.20.0)
 
 GEM
   remote: https://rubygems.org/
@@ -12,14 +12,16 @@ GEM
       rake
       thor (>= 0.14.0)
     ast (2.4.2)
-    diff-lcs (1.4.4)
-    parallel (1.20.1)
-    parser (3.0.2.0)
+    diff-lcs (1.5.0)
+    parallel (1.24.0)
+    parser (3.3.0.4)
       ast (~> 2.4.1)
-    rainbow (3.0.0)
-    rake (13.0.6)
-    regexp_parser (2.1.1)
-    rexml (3.2.5)
+      racc
+    racc (1.7.3)
+    rainbow (3.1.1)
+    rake (13.1.0)
+    regexp_parser (2.9.0)
+    rexml (3.2.6)
     rspec (3.5.0)
       rspec-core (~> 3.5.0)
       rspec-expectations (~> 3.5.0)
@@ -33,32 +35,32 @@ GEM
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.5.0)
     rspec-support (3.5.0)
-    rubocop (1.14.0)
+    rubocop (1.30.1)
       parallel (~> 1.10)
-      parser (>= 3.0.0.0)
+      parser (>= 3.1.0.0)
       rainbow (>= 2.2.2, < 4.0)
       regexp_parser (>= 1.8, < 3.0)
-      rexml
-      rubocop-ast (>= 1.5.0, < 2.0)
+      rexml (>= 3.2.5, < 4.0)
+      rubocop-ast (>= 1.18.0, < 2.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 1.4.0, < 3.0)
-    rubocop-ast (1.10.0)
-      parser (>= 3.0.1.1)
-    ruby-progressbar (1.11.0)
-    thor (1.1.0)
-    unicode-display_width (2.0.0)
+    rubocop-ast (1.30.0)
+      parser (>= 3.2.1.0)
+    ruby-progressbar (1.13.0)
+    thor (1.3.0)
+    unicode-display_width (2.5.0)
 
 PLATFORMS
-  java
   ruby
+  x86_64-darwin-22
 
 DEPENDENCIES
   appraisal (~> 2.4.1)
   bundler (>= 2.2.10)
   rake (>= 12.3.3)
   rspec (~> 3.5.0)
-  rubocop (= 1.14.0)
+  rubocop (= 1.30.1)
   rubocop-checkstyle_formatter!
 
 BUNDLED WITH
-   2.2.25
+   2.5.5
diff --git a/gemfiles/rubocop_1.17.0.gemfile b/gemfiles/rubocop_1.35.1.gemfile
similarity index 79%
rename from gemfiles/rubocop_1.17.0.gemfile
rename to gemfiles/rubocop_1.35.1.gemfile
index b8ed260..84630f6 100644
--- a/gemfiles/rubocop_1.17.0.gemfile
+++ b/gemfiles/rubocop_1.35.1.gemfile
@@ -2,6 +2,6 @@
 
 source "https://rubygems.org"
 
-gem "rubocop", "1.17.0"
+gem "rubocop", "1.35.1"
 
 gemspec path: "../"
diff --git a/gemfiles/rubocop_1.17.0.gemfile.lock b/gemfiles/rubocop_1.35.1.gemfile.lock
similarity index 63%
rename from gemfiles/rubocop_1.17.0.gemfile.lock
rename to gemfiles/rubocop_1.35.1.gemfile.lock
index cf2277c..6aaab13 100644
--- a/gemfiles/rubocop_1.17.0.gemfile.lock
+++ b/gemfiles/rubocop_1.35.1.gemfile.lock
@@ -2,7 +2,7 @@ PATH
   remote: ..
   specs:
     rubocop-checkstyle_formatter (0.5.0)
-      rubocop (>= 1.14.0)
+      rubocop (>= 1.20.0)
 
 GEM
   remote: https://rubygems.org/
@@ -12,14 +12,17 @@ GEM
       rake
       thor (>= 0.14.0)
     ast (2.4.2)
-    diff-lcs (1.4.4)
-    parallel (1.20.1)
-    parser (3.0.2.0)
+    diff-lcs (1.5.0)
+    json (2.7.1)
+    parallel (1.24.0)
+    parser (3.3.0.4)
       ast (~> 2.4.1)
-    rainbow (3.0.0)
-    rake (13.0.6)
-    regexp_parser (2.1.1)
-    rexml (3.2.5)
+      racc
+    racc (1.7.3)
+    rainbow (3.1.1)
+    rake (13.1.0)
+    regexp_parser (2.9.0)
+    rexml (3.2.6)
     rspec (3.5.0)
       rspec-core (~> 3.5.0)
       rspec-expectations (~> 3.5.0)
@@ -33,32 +36,33 @@ GEM
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.5.0)
     rspec-support (3.5.0)
-    rubocop (1.17.0)
+    rubocop (1.35.1)
+      json (~> 2.3)
       parallel (~> 1.10)
-      parser (>= 3.0.0.0)
+      parser (>= 3.1.2.1)
       rainbow (>= 2.2.2, < 4.0)
       regexp_parser (>= 1.8, < 3.0)
-      rexml
-      rubocop-ast (>= 1.7.0, < 2.0)
+      rexml (>= 3.2.5, < 4.0)
+      rubocop-ast (>= 1.20.1, < 2.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 1.4.0, < 3.0)
-    rubocop-ast (1.10.0)
-      parser (>= 3.0.1.1)
-    ruby-progressbar (1.11.0)
-    thor (1.1.0)
-    unicode-display_width (2.0.0)
+    rubocop-ast (1.30.0)
+      parser (>= 3.2.1.0)
+    ruby-progressbar (1.13.0)
+    thor (1.3.0)
+    unicode-display_width (2.5.0)
 
 PLATFORMS
-  java
   ruby
+  x86_64-darwin-22
 
 DEPENDENCIES
   appraisal (~> 2.4.1)
   bundler (>= 2.2.10)
   rake (>= 12.3.3)
   rspec (~> 3.5.0)
-  rubocop (= 1.17.0)
+  rubocop (= 1.35.1)
   rubocop-checkstyle_formatter!
 
 BUNDLED WITH
-   2.2.25
+   2.5.5
diff --git a/gemfiles/rubocop_1.40.0.gemfile b/gemfiles/rubocop_1.40.0.gemfile
new file mode 100644
index 0000000..bd26211
--- /dev/null
+++ b/gemfiles/rubocop_1.40.0.gemfile
@@ -0,0 +1,7 @@
+# This file was generated by Appraisal
+
+source "https://rubygems.org"
+
+gem "rubocop", "1.40.0"
+
+gemspec path: "../"
diff --git a/gemfiles/rubocop_1.15.0.gemfile.lock b/gemfiles/rubocop_1.40.0.gemfile.lock
similarity index 63%
rename from gemfiles/rubocop_1.15.0.gemfile.lock
rename to gemfiles/rubocop_1.40.0.gemfile.lock
index 50b869f..f4a1963 100644
--- a/gemfiles/rubocop_1.15.0.gemfile.lock
+++ b/gemfiles/rubocop_1.40.0.gemfile.lock
@@ -2,7 +2,7 @@ PATH
   remote: ..
   specs:
     rubocop-checkstyle_formatter (0.5.0)
-      rubocop (>= 1.14.0)
+      rubocop (>= 1.20.0)
 
 GEM
   remote: https://rubygems.org/
@@ -12,14 +12,17 @@ GEM
       rake
       thor (>= 0.14.0)
     ast (2.4.2)
-    diff-lcs (1.4.4)
-    parallel (1.20.1)
-    parser (3.0.2.0)
+    diff-lcs (1.5.0)
+    json (2.7.1)
+    parallel (1.24.0)
+    parser (3.3.0.4)
       ast (~> 2.4.1)
-    rainbow (3.0.0)
-    rake (13.0.6)
-    regexp_parser (2.1.1)
-    rexml (3.2.5)
+      racc
+    racc (1.7.3)
+    rainbow (3.1.1)
+    rake (13.1.0)
+    regexp_parser (2.9.0)
+    rexml (3.2.6)
     rspec (3.5.0)
       rspec-core (~> 3.5.0)
       rspec-expectations (~> 3.5.0)
@@ -33,32 +36,33 @@ GEM
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.5.0)
     rspec-support (3.5.0)
-    rubocop (1.15.0)
+    rubocop (1.40.0)
+      json (~> 2.3)
       parallel (~> 1.10)
-      parser (>= 3.0.0.0)
+      parser (>= 3.1.2.1)
       rainbow (>= 2.2.2, < 4.0)
       regexp_parser (>= 1.8, < 3.0)
-      rexml
-      rubocop-ast (>= 1.5.0, < 2.0)
+      rexml (>= 3.2.5, < 4.0)
+      rubocop-ast (>= 1.23.0, < 2.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 1.4.0, < 3.0)
-    rubocop-ast (1.10.0)
-      parser (>= 3.0.1.1)
-    ruby-progressbar (1.11.0)
-    thor (1.1.0)
-    unicode-display_width (2.0.0)
+    rubocop-ast (1.30.0)
+      parser (>= 3.2.1.0)
+    ruby-progressbar (1.13.0)
+    thor (1.3.0)
+    unicode-display_width (2.5.0)
 
 PLATFORMS
-  java
   ruby
+  x86_64-darwin-22
 
 DEPENDENCIES
   appraisal (~> 2.4.1)
   bundler (>= 2.2.10)
   rake (>= 12.3.3)
   rspec (~> 3.5.0)
-  rubocop (= 1.15.0)
+  rubocop (= 1.40.0)
   rubocop-checkstyle_formatter!
 
 BUNDLED WITH
-   2.2.25
+   2.5.5
diff --git a/gemfiles/rubocop_1.45.1.gemfile b/gemfiles/rubocop_1.45.1.gemfile
new file mode 100644
index 0000000..7915429
--- /dev/null
+++ b/gemfiles/rubocop_1.45.1.gemfile
@@ -0,0 +1,7 @@
+# This file was generated by Appraisal
+
+source "https://rubygems.org"
+
+gem "rubocop", "1.45.1"
+
+gemspec path: "../"
diff --git a/gemfiles/rubocop_1.45.1.gemfile.lock b/gemfiles/rubocop_1.45.1.gemfile.lock
new file mode 100644
index 0000000..2d74036
--- /dev/null
+++ b/gemfiles/rubocop_1.45.1.gemfile.lock
@@ -0,0 +1,68 @@
+PATH
+  remote: ..
+  specs:
+    rubocop-checkstyle_formatter (0.5.0)
+      rubocop (>= 1.20.0)
+
+GEM
+  remote: https://rubygems.org/
+  specs:
+    appraisal (2.4.1)
+      bundler
+      rake
+      thor (>= 0.14.0)
+    ast (2.4.2)
+    diff-lcs (1.5.0)
+    json (2.7.1)
+    parallel (1.24.0)
+    parser (3.3.0.4)
+      ast (~> 2.4.1)
+      racc
+    racc (1.7.3)
+    rainbow (3.1.1)
+    rake (13.1.0)
+    regexp_parser (2.9.0)
+    rexml (3.2.6)
+    rspec (3.5.0)
+      rspec-core (~> 3.5.0)
+      rspec-expectations (~> 3.5.0)
+      rspec-mocks (~> 3.5.0)
+    rspec-core (3.5.4)
+      rspec-support (~> 3.5.0)
+    rspec-expectations (3.5.0)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.5.0)
+    rspec-mocks (3.5.0)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.5.0)
+    rspec-support (3.5.0)
+    rubocop (1.45.1)
+      json (~> 2.3)
+      parallel (~> 1.10)
+      parser (>= 3.2.0.0)
+      rainbow (>= 2.2.2, < 4.0)
+      regexp_parser (>= 1.8, < 3.0)
+      rexml (>= 3.2.5, < 4.0)
+      rubocop-ast (>= 1.24.1, < 2.0)
+      ruby-progressbar (~> 1.7)
+      unicode-display_width (>= 2.4.0, < 3.0)
+    rubocop-ast (1.30.0)
+      parser (>= 3.2.1.0)
+    ruby-progressbar (1.13.0)
+    thor (1.3.0)
+    unicode-display_width (2.5.0)
+
+PLATFORMS
+  ruby
+  x86_64-darwin-22
+
+DEPENDENCIES
+  appraisal (~> 2.4.1)
+  bundler (>= 2.2.10)
+  rake (>= 12.3.3)
+  rspec (~> 3.5.0)
+  rubocop (= 1.45.1)
+  rubocop-checkstyle_formatter!
+
+BUNDLED WITH
+   2.5.5
diff --git a/gemfiles/rubocop_1.50.2.gemfile b/gemfiles/rubocop_1.50.2.gemfile
new file mode 100644
index 0000000..fea0e85
--- /dev/null
+++ b/gemfiles/rubocop_1.50.2.gemfile
@@ -0,0 +1,7 @@
+# This file was generated by Appraisal
+
+source "https://rubygems.org"
+
+gem "rubocop", "1.50.2"
+
+gemspec path: "../"
diff --git a/gemfiles/rubocop_1.50.2.gemfile.lock b/gemfiles/rubocop_1.50.2.gemfile.lock
new file mode 100644
index 0000000..7a41cab
--- /dev/null
+++ b/gemfiles/rubocop_1.50.2.gemfile.lock
@@ -0,0 +1,68 @@
+PATH
+  remote: ..
+  specs:
+    rubocop-checkstyle_formatter (0.5.0)
+      rubocop (>= 1.20.0)
+
+GEM
+  remote: https://rubygems.org/
+  specs:
+    appraisal (2.4.1)
+      bundler
+      rake
+      thor (>= 0.14.0)
+    ast (2.4.2)
+    diff-lcs (1.5.0)
+    json (2.7.1)
+    parallel (1.24.0)
+    parser (3.3.0.4)
+      ast (~> 2.4.1)
+      racc
+    racc (1.7.3)
+    rainbow (3.1.1)
+    rake (13.1.0)
+    regexp_parser (2.9.0)
+    rexml (3.2.6)
+    rspec (3.5.0)
+      rspec-core (~> 3.5.0)
+      rspec-expectations (~> 3.5.0)
+      rspec-mocks (~> 3.5.0)
+    rspec-core (3.5.4)
+      rspec-support (~> 3.5.0)
+    rspec-expectations (3.5.0)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.5.0)
+    rspec-mocks (3.5.0)
+      diff-lcs (>= 1.2.0, < 2.0)
+      rspec-support (~> 3.5.0)
+    rspec-support (3.5.0)
+    rubocop (1.50.2)
+      json (~> 2.3)
+      parallel (~> 1.10)
+      parser (>= 3.2.0.0)
+      rainbow (>= 2.2.2, < 4.0)
+      regexp_parser (>= 1.8, < 3.0)
+      rexml (>= 3.2.5, < 4.0)
+      rubocop-ast (>= 1.28.0, < 2.0)
+      ruby-progressbar (~> 1.7)
+      unicode-display_width (>= 2.4.0, < 3.0)
+    rubocop-ast (1.30.0)
+      parser (>= 3.2.1.0)
+    ruby-progressbar (1.13.0)
+    thor (1.3.0)
+    unicode-display_width (2.5.0)
+
+PLATFORMS
+  ruby
+  x86_64-darwin-22
+
+DEPENDENCIES
+  appraisal (~> 2.4.1)
+  bundler (>= 2.2.10)
+  rake (>= 12.3.3)
+  rspec (~> 3.5.0)
+  rubocop (= 1.50.2)
+  rubocop-checkstyle_formatter!
+
+BUNDLED WITH
+   2.5.5
diff --git a/rubocop-checkstyle_formatter.gemspec b/rubocop-checkstyle_formatter.gemspec
index 70698ac..46da202 100644
--- a/rubocop-checkstyle_formatter.gemspec
+++ b/rubocop-checkstyle_formatter.gemspec
@@ -1,4 +1,4 @@
-# -*- encoding: utf-8 -*-
+# frozen_string_literal: true
 
 require 'English'
 lib = File.expand_path('../lib', __FILE__)
@@ -19,7 +19,7 @@ Gem::Specification.new do |gem|
   gem.test_files    = gem.files.grep(%r{^(test|spec|features)/})
   gem.require_paths = ['lib']
 
-  gem.add_dependency 'rubocop', '>= 1.14.0'
+  gem.add_dependency 'rubocop', '>= 1.20.0'
   gem.add_development_dependency 'appraisal', '~> 2.4.1'
   gem.add_development_dependency 'bundler', '>= 2.2.10'
   gem.add_development_dependency 'rake', '>= 12.3.3'
diff --git a/spec/rubocop/formatter/checkstyle_formatter_spec.rb b/spec/rubocop/formatter/checkstyle_formatter_spec.rb
index 42afdf5..5e68406 100644
--- a/spec/rubocop/formatter/checkstyle_formatter_spec.rb
+++ b/spec/rubocop/formatter/checkstyle_formatter_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'stringio'
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 1c97172..7c48bc1 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 $LOAD_PATH.unshift(File.absolute_path('../../lib', __FILE__))
 require 'rspec'