How many options do we have to sort a Hashmap in Java 8?
Introduction
- As a developer, we often need some data structure to store than data and then perform some operations such as sort or filter on that data so that we can satisfy the business requirement.
- In this article, we will explore how can we sort HashMap in Java
- Our Map data structure consists of a news article as value and key as the tag of the article. We would sort the map based on tags.
Java Collections Class
- Java collections class expects list input for its sorting method.
Hence we need to provide a list created from the map. - Our output would be sorted based on tags.
- We can further modify the code using Comparator.comparing and using method reference for sorting using the key.
Java 8 Streams API
- We can use the sorted method on the stream of the entry set and provide sorting logic as a lambda function. Here we are sorting based on the tags of the news articles.
- We can use a method reference to make our code shorter and better to read.
- Our output would be sorted based on tags in ascending order of tags
- We can sort the map using value as well. newsMap has news object as value & we will sort using the title of the article.
- Below is our sorted output based on the values of the map.
- We can also reverse the order by value
- Output is based on reverse order of title of the news
Conclusion
- We can sort the map using the Collections class sort method. A sort method only accepts lists, we need to convert a hashmap into an entry set and create a list of entry set from it. Then we can pass out list and comparator logic to sort the data either based on key or value.
- We can also use Java Stream API, convert it to an entry set and perform sort operations by providing comparator logic.
- Both the options look fine to sort the hashmap, although lambda and method reference can be used with both the approach to avoid boilerplate code.
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