Скачать или смотреть How to Sort a HashMap by Key Insertion Order in Java

Discover how to maintain the order of key insertion in a `HashMap` using `LinkedHashMap` in Java to achieve customizable sorting.
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How to Sort a HashMap by Key Insertion Order in Java

When working with collections in Java, one common problem developers encounter is the need to maintain the order of insertion for keys in a HashMap. By default, a HashMap does not guarantee any specific order of its elements, which can be frustrating when you want to display the keys in a particular sequence. In this post, we will explore how to overcome this limitation using a LinkedHashMap.

Understanding the Problem

Consider a scenario where you have a HashMap populated with string keys and values. For instance:

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When you iterate over the keys and print them, you will get an output that appears unordered:

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However, for your application, you require the output in a creative order like:

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How can you achieve this? Let’s delve into the solution!

The Solution: Using LinkedHashMap

To maintain the order of key insertion while allowing for custom sorting, you can use a LinkedHashMap. This class maintains a doubly linked list to maintain the order of its elements. Here’s how you can implement it:

Step 1: Initialize a LinkedHashMap

Replace your HashMap with LinkedHashMap:

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Step 2: Print the Keys

When you iterate through the keys of the LinkedHashMap, they will be printed in the order you inserted them:

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Final Code Example

Here’s the complete code snippet that demonstrates the solution:

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Output

When you execute the above code, you will receive the desired output:

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Conclusion

Using a LinkedHashMap is a simple yet effective solution for maintaining the order of key insertion in Java. This allows you to control how items are displayed or processed, which can be crucial in many applications.

Now that you know how to achieve creative order output with a LinkedHashMap, you can implement it in your projects or any other situations where order matters in your key-value pairs. Happy coding!