Map .

Which Map Allows Duplicate Keys In Java?

Written by Ben Javu Mar 30, 2023 ยท 3 min read
Which Map Allows Duplicate Keys In Java?

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Can Map Have Duplicate Keys Topographic Map of Usa with States
Can Map Have Duplicate Keys Topographic Map of Usa with States from topographicmapofusawithstates.github.io

Introduction

When it comes to Java programming, Maps are a crucial part of the language. They allow developers to store and manipulate data in a way that is efficient and effective. However, one question that often arises is whether or not duplicate keys are allowed in Maps. In this article, we will explore which Map allows duplicate keys in Java.

The Basics of Maps

Before we dive into the question at hand, let's first review the basics of Maps. A Map is a collection of key-value pairs. Each key in the Map is unique, and the value associated with that key can be any object. In Java, there are several types of Maps, including HashMap, TreeMap, and LinkedHashMap.

HashMap

HashMap is a type of Map that allows for duplicate values, but not duplicate keys. When a duplicate key is added to a HashMap, the previous value associated with that key is overwritten by the new value.

TreeMap

TreeMap, on the other hand, does not allow for duplicate keys. If a duplicate key is added to a TreeMap, the previous value associated with that key is replaced by the new value.

LinkedHashMap

LinkedHashMap is similar to HashMap in that it allows for duplicate values, but not duplicate keys. However, unlike HashMap, LinkedHashMap maintains the order in which keys were inserted into the Map.

Which Map Allows Duplicate Keys?

So, which Map allows duplicate keys in Java? The answer is none of them. In Java, Maps do not allow for duplicate keys. If you try to add a duplicate key to a Map, the previous value associated with that key will be overwritten by the new value.

But What if I Need to Store Duplicate Keys?

While Maps do not allow for duplicate keys, there are ways to store duplicate keys in Java. One way is to use a List to store the values associated with each key. For example, you could create a Map> to store a list of values for each key.

Conclusion

In conclusion, Maps are an essential part of Java programming. While they do not allow for duplicate keys, there are ways to work around this limitation. By using a List to store values associated with each key, developers can effectively store and manipulate data in their Java programs.

Q&A

Q: Can I use HashSet to store duplicate keys?

A: No, HashSet does not allow for duplicate keys. If you try to add a duplicate key to a HashSet, the previous value associated with that key will be overwritten by the new value.

Q: Is it possible to retrieve duplicate keys from a Map?

A: No, it is not possible to retrieve duplicate keys from a Map. When a duplicate key is added to a Map, the previous value associated with that key is overwritten by the new value. However, as mentioned earlier, it is possible to store a list of values for each key in a Map to work around this limitation.
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