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Singleton

Solution

• Simple

@startuml
class Singleton {
    - instance: Singleton {static}
    - Singleton()
    + getInstance(): Singleton {static}
}
@enduml

• Inner Class

@startuml
class Singleton {
    - Singleton()
    + getInstance(): Singleton {static}
}

-class InstanceHolder {
    - instance: Singleton {static}
}

Singleton +. InstanceHolder 
@enduml

• Enumeration

@startuml
enum Singleton {
    + INSTANCE {static}
}
@enduml

Issues

• Thread Safe
  • volatile
  • synchronized
• Uniqueness
  • Class Load
  • Clone
  • Reflect
  • Deserialize

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