From fd34d7b3cdbb2ea8cf9dae87d1237c6b1474167b Mon Sep 17 00:00:00 2001
From: Dawand Sulaiman <djs21@st-andrews.ac.uk>
Date: Sat, 2 Jan 2021 00:19:30 +0000
Subject: [PATCH] Add Singleton example to Design Patterns

---
 .../Advanced-Java.iml                         |   0
 .../CompletableFutureExample.class            | Bin
 .../Advanced-Java/Callbacks/Callbacks.class   | Bin
 .../Callbacks/Lambdas$Service.class           | Bin
 .../Advanced-Java/Callbacks/Lambdas.class     | Bin
 .../CombinatorPattern/Customer.class          | Bin
 .../CustomerRegistrationValidator.class       | Bin
 .../CustomerValidatorService.class            | Bin
 .../CombinatorPattern/Main.class              | Bin
 .../CombinatorPattern/ValidationResult.class  | Bin
 .../Concurrency/ConditionExample.class        | Bin
 .../Concurrency/ThreadLocalExample.class      | Bin
 .../Concurrency/ThreadSafeFormatter.class     | Bin
 .../VolatileOrAtomic$FlagChecker.class        | Bin
 .../VolatileOrAtomic$FlagUpdater.class        | Bin
 .../Concurrency/VolatileOrAtomic.class        | Bin
 .../DesignPatterns/TaxCalculator.class        | Bin
 .../DesignPatterns/TaxCalculator2019.class    | Bin
 .../DesignPatterns/TaxCalculator2020.class    | Bin
 .../Advanced-Java/DesignPatterns/User.class   | Bin
 .../DesignPatterns/memento/Editor.class       | Bin
 .../DesignPatterns/memento/EditorState.class  | Bin
 .../DesignPatterns/memento/History.class      | Bin
 .../DesignPatterns/memento/Main.class         | Bin
 .../DesignPatterns/state/BrushTool.class      | Bin
 .../DesignPatterns/state/Canvas.class         | Bin
 .../DesignPatterns/state/Main.class           | Bin
 .../DesignPatterns/state/Selection.class      | Bin
 .../DesignPatterns/state/Tool.class           | Bin
 .../DesignPatterns/state/ToolType.class       | Bin
 .../FunctionalProgramming/Gender.class        | Bin
 .../FunctionalProgramming/Main.class          | Bin
 .../FunctionalProgramming/Person.class        | Bin
 .../FunctionalProgramming/_Function.class     | Bin
 .../FunctionalProgramming/_Predicate.class    | Bin
 .../FunctionalProgramming/_Supplier.class     | Bin
 .../META-INF/Advanced-Java.kotlin_module      | Bin
 .../Advanced-Java/Optionals/_Optionals.class  | Bin
 .../Advanced-Java/csv_reader/CSVReader.class  | Bin
 .../Advanced-Java/csv_reader/data.csv         |   0
 .../dsa_koffman_ch2/JUnitTest.class           | Bin
 .../dsa_koffman_ch2/OrderedList.class         | Bin
 .../dsa_koffman_ch2/TestOrderedList.class     | Bin
 .../Advanced-Java/interfaces/Employee.class   | Bin
 .../Advanced-Java/interfaces/Person.class     | Bin
 .../interfaces/TaxCollector.class             | Bin
 .../Advanced-Java/interfaces/TaxPayer.class   | Bin
 .../java8_features/FunctionalInterfaces.class | Bin
 .../java8_features/GreetingService.class      | Bin
 .../Advanced-Java/java8_features/Lambda.class | Bin
 .../java8_features/LocalDateTimeExample.class | Bin
 .../java8_features/MathOperation.class        | Bin
 .../java8_features/MethodReference.class      | Bin
 .../Advanced-Java/java8_features/Stream.class | Bin
 .../java_gc/FinalizeExample.class             | Bin
 .../Advanced-Java/java_gc/Person.class        | Bin
 .../java_gc/PersonMetaData.class              | Bin
 .../java_gc/WeakHashMapExample.class          | Bin
 .../java_gc/WeakReferenceExample.class        | Bin
 .../CompletableFutureExample.java             |   0
 .../src/Callbacks/Callbacks.java              |   0
 .../src/Callbacks/Lambdas.java                |   0
 .../src/CombinatorPattern/Customer.java       |   0
 .../CustomerRegistrationValidator.java        |   0
 .../CustomerValidatorService.java             |   0
 .../src/CombinatorPattern/Main.java           |   0
 .../CombinatorPattern/ValidationResult.java   |   0
 .../src/Concurrency/ConditionExample.java     |   0
 .../src/Concurrency/MyRunnable.java           |   0
 .../src/Concurrency/MyRunnableMain.java       |   0
 .../src/Concurrency/ThreadLocalExample.java   |   0
 .../src/Concurrency/VolatileOrAtomic.java     |   0
 .../src/DesignPatterns/TaxCalculator.java     |   0
 .../src/DesignPatterns/TaxCalculator2019.java |   0
 .../src/DesignPatterns/TaxCalculator2020.java |   0
 .../src/DesignPatterns/User.java              |   0
 .../src/DesignPatterns/memento/Editor.java    |   0
 .../DesignPatterns/memento/EditorState.java   |   0
 .../src/DesignPatterns/memento/History.java   |   0
 .../src/DesignPatterns/memento/Main.java      |   0
 .../src/DesignPatterns/state/BrushTool.java   |   0
 .../src/DesignPatterns/state/Canvas.java      |   0
 .../src/DesignPatterns/state/Main.java        |   0
 .../src/DesignPatterns/state/Selection.java   |   0
 .../src/DesignPatterns/state/Tool.java        |   0
 .../src/DesignPatterns/state/ToolType.java    |   0
 .../src/FunctionalProgramming/Gender.java     |   0
 .../src/FunctionalProgramming/Main.java       |   0
 .../src/FunctionalProgramming/Person.java     |   0
 .../src/FunctionalProgramming/_Function.java  |   0
 .../src/FunctionalProgramming/_Predicate.java |   0
 .../src/FunctionalProgramming/_Supplier.java  |   0
 .../src/Optionals/_Optionals.java             |   0
 .../src/csv_reader/CSVReader.java             |   0
 .../src/csv_reader/data.csv                   |   0
 .../src/dsa_koffman_ch2/JUnitTest.java        |   0
 .../src/dsa_koffman_ch2/OrderedList.java      |   0
 .../src/dsa_koffman_ch2/TestOrderedList.java  |   0
 .../src/interfaces/Employee.java              |   0
 .../src/interfaces/Person.java                |   0
 .../src/interfaces/TaxCollector.java          |   0
 .../src/interfaces/TaxPayer.java              |   0
 .../java8_features/FunctionalInterfaces.java  |   0
 .../src/java8_features/Lambda.java            |   0
 .../java8_features/LocalDateTimeExample.java  |   0
 .../src/java8_features/MethodReference.java   |   0
 .../src/java8_features/Stream.java            |   0
 .../src/java_gc/FinalizeExample.java          |   0
 .../src/java_gc/WeakHashMapExample.java       |   0
 .../src/java_gc/WeakReferenceExample.java     |   0
 Design-patterns/src/singleton/Captain.java    |  21 ++++++++++++++++++
 .../src/singleton/SingletonExample.java       |  13 +++++++++++
 interview-preparation.iml                     |   1 +
 113 files changed, 35 insertions(+)
 rename {Java/Advanced-Java => Advanced-Java}/Advanced-Java.iml (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/AsyncProgramming/CompletableFutureExample.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/Callbacks/Callbacks.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/Callbacks/Lambdas$Service.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/Callbacks/Lambdas.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/CombinatorPattern/Customer.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/CombinatorPattern/CustomerRegistrationValidator.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/CombinatorPattern/CustomerValidatorService.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/CombinatorPattern/Main.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/CombinatorPattern/ValidationResult.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/Concurrency/ConditionExample.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/Concurrency/ThreadLocalExample.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/Concurrency/ThreadSafeFormatter.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/Concurrency/VolatileOrAtomic$FlagChecker.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/Concurrency/VolatileOrAtomic$FlagUpdater.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/Concurrency/VolatileOrAtomic.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/DesignPatterns/TaxCalculator.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/DesignPatterns/TaxCalculator2019.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/DesignPatterns/TaxCalculator2020.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/DesignPatterns/User.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/DesignPatterns/memento/Editor.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/DesignPatterns/memento/EditorState.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/DesignPatterns/memento/History.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/DesignPatterns/memento/Main.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/DesignPatterns/state/BrushTool.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/DesignPatterns/state/Canvas.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/DesignPatterns/state/Main.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/DesignPatterns/state/Selection.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/DesignPatterns/state/Tool.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/DesignPatterns/state/ToolType.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/FunctionalProgramming/Gender.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/FunctionalProgramming/Main.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/FunctionalProgramming/Person.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/FunctionalProgramming/_Function.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/FunctionalProgramming/_Predicate.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/FunctionalProgramming/_Supplier.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/META-INF/Advanced-Java.kotlin_module (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/Optionals/_Optionals.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/csv_reader/CSVReader.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/csv_reader/data.csv (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/dsa_koffman_ch2/JUnitTest.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/dsa_koffman_ch2/OrderedList.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/dsa_koffman_ch2/TestOrderedList.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/interfaces/Employee.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/interfaces/Person.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/interfaces/TaxCollector.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/interfaces/TaxPayer.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/java8_features/FunctionalInterfaces.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/java8_features/GreetingService.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/java8_features/Lambda.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/java8_features/LocalDateTimeExample.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/java8_features/MathOperation.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/java8_features/MethodReference.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/java8_features/Stream.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/java_gc/FinalizeExample.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/java_gc/Person.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/java_gc/PersonMetaData.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/java_gc/WeakHashMapExample.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/out/production/Advanced-Java/java_gc/WeakReferenceExample.class (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/AsyncProgramming/CompletableFutureExample.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/Callbacks/Callbacks.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/Callbacks/Lambdas.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/CombinatorPattern/Customer.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/CombinatorPattern/CustomerRegistrationValidator.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/CombinatorPattern/CustomerValidatorService.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/CombinatorPattern/Main.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/CombinatorPattern/ValidationResult.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/Concurrency/ConditionExample.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/Concurrency/MyRunnable.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/Concurrency/MyRunnableMain.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/Concurrency/ThreadLocalExample.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/Concurrency/VolatileOrAtomic.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/DesignPatterns/TaxCalculator.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/DesignPatterns/TaxCalculator2019.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/DesignPatterns/TaxCalculator2020.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/DesignPatterns/User.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/DesignPatterns/memento/Editor.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/DesignPatterns/memento/EditorState.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/DesignPatterns/memento/History.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/DesignPatterns/memento/Main.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/DesignPatterns/state/BrushTool.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/DesignPatterns/state/Canvas.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/DesignPatterns/state/Main.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/DesignPatterns/state/Selection.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/DesignPatterns/state/Tool.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/DesignPatterns/state/ToolType.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/FunctionalProgramming/Gender.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/FunctionalProgramming/Main.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/FunctionalProgramming/Person.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/FunctionalProgramming/_Function.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/FunctionalProgramming/_Predicate.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/FunctionalProgramming/_Supplier.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/Optionals/_Optionals.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/csv_reader/CSVReader.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/csv_reader/data.csv (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/dsa_koffman_ch2/JUnitTest.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/dsa_koffman_ch2/OrderedList.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/dsa_koffman_ch2/TestOrderedList.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/interfaces/Employee.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/interfaces/Person.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/interfaces/TaxCollector.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/interfaces/TaxPayer.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/java8_features/FunctionalInterfaces.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/java8_features/Lambda.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/java8_features/LocalDateTimeExample.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/java8_features/MethodReference.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/java8_features/Stream.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/java_gc/FinalizeExample.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/java_gc/WeakHashMapExample.java (100%)
 rename {Java/Advanced-Java => Advanced-Java}/src/java_gc/WeakReferenceExample.java (100%)
 create mode 100644 Design-patterns/src/singleton/Captain.java
 create mode 100644 Design-patterns/src/singleton/SingletonExample.java

diff --git a/Java/Advanced-Java/Advanced-Java.iml b/Advanced-Java/Advanced-Java.iml
similarity index 100%
rename from Java/Advanced-Java/Advanced-Java.iml
rename to Advanced-Java/Advanced-Java.iml
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/AsyncProgramming/CompletableFutureExample.class b/Advanced-Java/out/production/Advanced-Java/AsyncProgramming/CompletableFutureExample.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/AsyncProgramming/CompletableFutureExample.class
rename to Advanced-Java/out/production/Advanced-Java/AsyncProgramming/CompletableFutureExample.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/Callbacks/Callbacks.class b/Advanced-Java/out/production/Advanced-Java/Callbacks/Callbacks.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/Callbacks/Callbacks.class
rename to Advanced-Java/out/production/Advanced-Java/Callbacks/Callbacks.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/Callbacks/Lambdas$Service.class b/Advanced-Java/out/production/Advanced-Java/Callbacks/Lambdas$Service.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/Callbacks/Lambdas$Service.class
rename to Advanced-Java/out/production/Advanced-Java/Callbacks/Lambdas$Service.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/Callbacks/Lambdas.class b/Advanced-Java/out/production/Advanced-Java/Callbacks/Lambdas.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/Callbacks/Lambdas.class
rename to Advanced-Java/out/production/Advanced-Java/Callbacks/Lambdas.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/CombinatorPattern/Customer.class b/Advanced-Java/out/production/Advanced-Java/CombinatorPattern/Customer.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/CombinatorPattern/Customer.class
rename to Advanced-Java/out/production/Advanced-Java/CombinatorPattern/Customer.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/CombinatorPattern/CustomerRegistrationValidator.class b/Advanced-Java/out/production/Advanced-Java/CombinatorPattern/CustomerRegistrationValidator.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/CombinatorPattern/CustomerRegistrationValidator.class
rename to Advanced-Java/out/production/Advanced-Java/CombinatorPattern/CustomerRegistrationValidator.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/CombinatorPattern/CustomerValidatorService.class b/Advanced-Java/out/production/Advanced-Java/CombinatorPattern/CustomerValidatorService.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/CombinatorPattern/CustomerValidatorService.class
rename to Advanced-Java/out/production/Advanced-Java/CombinatorPattern/CustomerValidatorService.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/CombinatorPattern/Main.class b/Advanced-Java/out/production/Advanced-Java/CombinatorPattern/Main.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/CombinatorPattern/Main.class
rename to Advanced-Java/out/production/Advanced-Java/CombinatorPattern/Main.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/CombinatorPattern/ValidationResult.class b/Advanced-Java/out/production/Advanced-Java/CombinatorPattern/ValidationResult.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/CombinatorPattern/ValidationResult.class
rename to Advanced-Java/out/production/Advanced-Java/CombinatorPattern/ValidationResult.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/Concurrency/ConditionExample.class b/Advanced-Java/out/production/Advanced-Java/Concurrency/ConditionExample.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/Concurrency/ConditionExample.class
rename to Advanced-Java/out/production/Advanced-Java/Concurrency/ConditionExample.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/Concurrency/ThreadLocalExample.class b/Advanced-Java/out/production/Advanced-Java/Concurrency/ThreadLocalExample.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/Concurrency/ThreadLocalExample.class
rename to Advanced-Java/out/production/Advanced-Java/Concurrency/ThreadLocalExample.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/Concurrency/ThreadSafeFormatter.class b/Advanced-Java/out/production/Advanced-Java/Concurrency/ThreadSafeFormatter.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/Concurrency/ThreadSafeFormatter.class
rename to Advanced-Java/out/production/Advanced-Java/Concurrency/ThreadSafeFormatter.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/Concurrency/VolatileOrAtomic$FlagChecker.class b/Advanced-Java/out/production/Advanced-Java/Concurrency/VolatileOrAtomic$FlagChecker.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/Concurrency/VolatileOrAtomic$FlagChecker.class
rename to Advanced-Java/out/production/Advanced-Java/Concurrency/VolatileOrAtomic$FlagChecker.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/Concurrency/VolatileOrAtomic$FlagUpdater.class b/Advanced-Java/out/production/Advanced-Java/Concurrency/VolatileOrAtomic$FlagUpdater.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/Concurrency/VolatileOrAtomic$FlagUpdater.class
rename to Advanced-Java/out/production/Advanced-Java/Concurrency/VolatileOrAtomic$FlagUpdater.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/Concurrency/VolatileOrAtomic.class b/Advanced-Java/out/production/Advanced-Java/Concurrency/VolatileOrAtomic.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/Concurrency/VolatileOrAtomic.class
rename to Advanced-Java/out/production/Advanced-Java/Concurrency/VolatileOrAtomic.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/DesignPatterns/TaxCalculator.class b/Advanced-Java/out/production/Advanced-Java/DesignPatterns/TaxCalculator.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/DesignPatterns/TaxCalculator.class
rename to Advanced-Java/out/production/Advanced-Java/DesignPatterns/TaxCalculator.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/DesignPatterns/TaxCalculator2019.class b/Advanced-Java/out/production/Advanced-Java/DesignPatterns/TaxCalculator2019.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/DesignPatterns/TaxCalculator2019.class
rename to Advanced-Java/out/production/Advanced-Java/DesignPatterns/TaxCalculator2019.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/DesignPatterns/TaxCalculator2020.class b/Advanced-Java/out/production/Advanced-Java/DesignPatterns/TaxCalculator2020.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/DesignPatterns/TaxCalculator2020.class
rename to Advanced-Java/out/production/Advanced-Java/DesignPatterns/TaxCalculator2020.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/DesignPatterns/User.class b/Advanced-Java/out/production/Advanced-Java/DesignPatterns/User.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/DesignPatterns/User.class
rename to Advanced-Java/out/production/Advanced-Java/DesignPatterns/User.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/DesignPatterns/memento/Editor.class b/Advanced-Java/out/production/Advanced-Java/DesignPatterns/memento/Editor.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/DesignPatterns/memento/Editor.class
rename to Advanced-Java/out/production/Advanced-Java/DesignPatterns/memento/Editor.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/DesignPatterns/memento/EditorState.class b/Advanced-Java/out/production/Advanced-Java/DesignPatterns/memento/EditorState.class
similarity index 100%
rename from Java/Advanced-Java/out/production/Advanced-Java/DesignPatterns/memento/EditorState.class
rename to Advanced-Java/out/production/Advanced-Java/DesignPatterns/memento/EditorState.class
diff --git a/Java/Advanced-Java/out/production/Advanced-Java/DesignPatterns/memento/History.class b/Advanced-Java/out/production/Advanced-Java/DesignPatterns/memento/History.class
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diff --git a/Java/Advanced-Java/src/interfaces/TaxPayer.java b/Advanced-Java/src/interfaces/TaxPayer.java
similarity index 100%
rename from Java/Advanced-Java/src/interfaces/TaxPayer.java
rename to Advanced-Java/src/interfaces/TaxPayer.java
diff --git a/Java/Advanced-Java/src/java8_features/FunctionalInterfaces.java b/Advanced-Java/src/java8_features/FunctionalInterfaces.java
similarity index 100%
rename from Java/Advanced-Java/src/java8_features/FunctionalInterfaces.java
rename to Advanced-Java/src/java8_features/FunctionalInterfaces.java
diff --git a/Java/Advanced-Java/src/java8_features/Lambda.java b/Advanced-Java/src/java8_features/Lambda.java
similarity index 100%
rename from Java/Advanced-Java/src/java8_features/Lambda.java
rename to Advanced-Java/src/java8_features/Lambda.java
diff --git a/Java/Advanced-Java/src/java8_features/LocalDateTimeExample.java b/Advanced-Java/src/java8_features/LocalDateTimeExample.java
similarity index 100%
rename from Java/Advanced-Java/src/java8_features/LocalDateTimeExample.java
rename to Advanced-Java/src/java8_features/LocalDateTimeExample.java
diff --git a/Java/Advanced-Java/src/java8_features/MethodReference.java b/Advanced-Java/src/java8_features/MethodReference.java
similarity index 100%
rename from Java/Advanced-Java/src/java8_features/MethodReference.java
rename to Advanced-Java/src/java8_features/MethodReference.java
diff --git a/Java/Advanced-Java/src/java8_features/Stream.java b/Advanced-Java/src/java8_features/Stream.java
similarity index 100%
rename from Java/Advanced-Java/src/java8_features/Stream.java
rename to Advanced-Java/src/java8_features/Stream.java
diff --git a/Java/Advanced-Java/src/java_gc/FinalizeExample.java b/Advanced-Java/src/java_gc/FinalizeExample.java
similarity index 100%
rename from Java/Advanced-Java/src/java_gc/FinalizeExample.java
rename to Advanced-Java/src/java_gc/FinalizeExample.java
diff --git a/Java/Advanced-Java/src/java_gc/WeakHashMapExample.java b/Advanced-Java/src/java_gc/WeakHashMapExample.java
similarity index 100%
rename from Java/Advanced-Java/src/java_gc/WeakHashMapExample.java
rename to Advanced-Java/src/java_gc/WeakHashMapExample.java
diff --git a/Java/Advanced-Java/src/java_gc/WeakReferenceExample.java b/Advanced-Java/src/java_gc/WeakReferenceExample.java
similarity index 100%
rename from Java/Advanced-Java/src/java_gc/WeakReferenceExample.java
rename to Advanced-Java/src/java_gc/WeakReferenceExample.java
diff --git a/Design-patterns/src/singleton/Captain.java b/Design-patterns/src/singleton/Captain.java
new file mode 100644
index 0000000..dd9c36a
--- /dev/null
+++ b/Design-patterns/src/singleton/Captain.java
@@ -0,0 +1,21 @@
+package singleton;
+
+// final is to avoid having non-static nested classes subclassing Captain
+final class Captain {
+
+    private static Captain captain;
+
+    private Captain() {}
+
+    // synchronized is for multithreaded purpose
+    public static synchronized Captain getInstance() {
+        if (captain == null) { // lazy initialization
+            captain = new Captain();
+            System.out.println("A new captain is created :)");
+            return captain;
+        } else {
+            System.out.println("You already have a captain!");
+        }
+            return captain;
+    }
+}
diff --git a/Design-patterns/src/singleton/SingletonExample.java b/Design-patterns/src/singleton/SingletonExample.java
new file mode 100644
index 0000000..6d8e430
--- /dev/null
+++ b/Design-patterns/src/singleton/SingletonExample.java
@@ -0,0 +1,13 @@
+package singleton;
+
+public class SingletonExample {
+    public static void main(String[] args) {
+        Captain captain1 = Captain.getInstance();
+        Captain captain2 = Captain.getInstance();
+
+        if (captain1 == captain2) {
+            System.out.println("Captain 1 and 2 are same instances");
+        }
+
+    }
+}
diff --git a/interview-preparation.iml b/interview-preparation.iml
index 81ac92b..9dbde82 100644
--- a/interview-preparation.iml
+++ b/interview-preparation.iml
@@ -4,6 +4,7 @@
     <exclude-output />
     <content url="file://$MODULE_DIR$">
       <sourceFolder url="file://$MODULE_DIR$/problems" isTestSource="false" />
+      <sourceFolder url="file://$MODULE_DIR$/Design-patterns/src" isTestSource="false" />
     </content>
     <orderEntry type="inheritedJdk" />
     <orderEntry type="sourceFolder" forTests="false" />