In Java, a Map refers to an object that would represent a mapping from various unique keys to the values. Various useful java.util.Map interfaces implementations are available with the Java language, like LinkedHashMap, TreeMap, and HashMap. These are somewhat similar in their functionalities, but there is a significant difference between HashMap, TreeMap and LinkedHashMap. In this article, we are going to discuss the same in brief. Read ahead to learn more about their differences.
What is TreeMap?
The primary function of TreeMap is to maintain order. It helps us in the storage of keys in a sorted manner in ascending order. For insertion and hookup, it has O(logN) complexity. It does not allow any null key, but it definitely allows null values.
What is HashMap?
The HashMap does not function to maintain any order. For insertion and hookup, it has O(1) complexity. It only allows a single null key, but it allows multiple numbers of null values.
What is LinkedHashMap?
The primary function of the LinkedHashMap is to maintain an order in which we would insert the key-value pairs. For insertion and hookup, the complexity of LinkedHashMap is O(1). It also allows us with a single null key as well as multiple numbers of null values.
Differences between TreeMap, HashMap and LinkedHashMap in Java
Let us talk about the differences between TreeMap, HashMap, and LinkedHashMap in Java.
| Parameters | TreeMap | HashMap | LinkedHashMap |
| Insertion and Hookup | For insertion and hookup, it has O(logN) complexity. | For insertion and hookup, it has O(1) complexity. | For insertion and hookup, the complexity of LinkedHashMap is O(1). |
| Null Keys | It does not allow any null key. | It only allows a single null key. | It only allows a single null key. |
| Null Values | It allows null values. | It allows multiple numbers of null values. | It allows multiple numbers of null values. |
| Maintaining Order | The primary function of TreeMap is to maintain order. It helps us in the storage of keys in a sorted manner in ascending order. | The HashMap does not function to maintain any order. | The primary function of the LinkedHashMap is to maintain an order in which we would insert the key-value pairs. |
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