Which two are elements of a singleton class? (Choose two.)

Question

Options

• Aa transient reference to point to the single instance
• Ba public method to instantiate the single instance
• Ca public static method to return a copy of the singleton reference
• Da private constructor to the class
• Ea public reference to point to the single instance

• A
  9% (2)
• B
  73% (16)
• C
  5% (1)
• E
  14% (3)

Explanation

A singleton class requires a private constructor (D) to prevent external code from creating new instances directly, and a public method (B) - typically called getInstance() - that controls access to the one and only instance, creating it on first call and returning the existing one thereafter.

Why the distractors are wrong:

• A - transient is a Java keyword that excludes a field from serialization; it has no role in defining a singleton.
• C - The getInstance() method returns the actual singleton reference, not a copy. Returning a copy would defeat the purpose of enforcing a single instance.
• E - The internal static reference must be private, not public. Exposing it publicly would let callers reassign or misuse it, breaking the singleton guarantee.

Memory tip: Think "lock the door, provide the key" - the private constructor locks the door so no one can new their way in, and the public method is the only key that controls entry to the single instance.

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