![]() ![]() In other words, it does not allow duplicate keys in the map. The default behaviour of the Collector returned by the toMap method seen above is to throw an IllegalStateException when more than one input element from the stream gets mapped to the same key. Collectors.toMap – Overloads Merge functionĪ couple of overloads exist for the toMap method. Similarly, the valueMapper is used to derive the map value from the input. The output of that mapper will be used as the map key. An input element from the stream is passed to the keyMapper. These functions are used to derive the key and value. Returns a Collector that accumulates elements into a Map whose keys and values are the result of applying the provided mapping functions to the input elements.Ī basic toMap method takes a key mapper and a value mapper. In this blog post, I will demonstrate the Java 8 Collectors.toMap method with examples and how it’s used to fold a stream into a map. ![]() It is used to reduce the stream of objects into a map. The toMap static method in the Collectors class provides one such Collector instance. The collect method mentioned earlier takes a Collector instance. Examples include finding the sum or minimum of a set of numbers. It involves taking the individual data or elements from the stream combining into a single result container by applying a combining operation. A mutable reduction operation is also known as a fold operation. When using the Java 8 streams API, we can use the collect method to perform mutable reductions on the data stream. ![]()
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