Suppose that you would like to create an instance of a new Map that has an iteration order that is the same as the iteration order of an existing instance of a Map. Which concrete implementation of the Map interface should be used for the new instance?
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TreeMap
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HashMap
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LinkedHashMap
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The answer depends on the implementation of the existing instance.
To solve this question, the user needs to know the differences between the concrete implementations of the Map interface and their iteration orders.
Now, let's go through each option and explain why it is right or wrong:
A. TreeMap: This option is incorrect because TreeMap sorts its elements in natural order or by a custom Comparator, whereas the iteration order of the existing instance of the Map may not be sorted. Thus, creating a new instance of TreeMap would not preserve the same iteration order as the existing instance.
B. HashMap: This option is incorrect because HashMap does not guarantee any particular iteration order. Thus, creating a new instance of HashMap would not preserve the same iteration order as the existing instance.
C. LinkedHashMap: This option is correct. LinkedHashMap is similar to HashMap but maintains a doubly-linked list running through all its entries, which allows it to maintain the insertion order. Thus, creating a new instance of LinkedHashMap would preserve the same iteration order as the existing instance.
D. The answer depends on the implementation of the existing instance: This option is incorrect because the iteration order of the existing instance of the Map may not be guaranteed by all implementations of the Map interface. Thus, it is not a reliable solution to assume that any implementation of the Map interface would preserve the same iteration order as the existing instance.
The Answer is: C. LinkedHashMap
LinkedHashMap maintains a doubly-linked list running through its entries, preserving insertion order (or optionally access order) — so an iteration over a LinkedHashMap built by copying an existing Map preserves that Map's original iteration order, making it the right choice to replicate an existing instance's ordering. HashMap gives no ordering guarantee at all — its iteration order depends on hash codes and bucket layout, not insertion order. TreeMap imposes its own sorted order (by key comparator), overriding whatever order the source Map had. The last option is a distractor; LinkedHashMap's ordering behavior is well-defined regardless of what the source Map's implementation was.