For that, I can use the map() method of class. In order to find the even numbers, I first need to convert a List of String to a List of Integer. I want to process this list and need another List of Integer with just even numbers. Since String and Integer are the most common data type in Java, I have chosen an example that is both simple and interesting. You need a good example to understand any new concept.
If you are not familiar with Stream behavior, I suggest you check out The Ultimate Java 9 Tutorial, which further explains Stream fundamentals in great detail. The filter() method is also lazy, meaning it will not be evaluated until you call a reduction method, like collect, and it will stop as soon as it reaches the target. Similar to map, the filter is also an intermediate operation, which means you can call other Stream methods after calling the filter. If the condition evaluates true, the object is selected. That's why the filter (Predicate condition) accepts a Predicate object, which provides a function that is applied to a condition. The filter method essentially selects elements based on a condition you provide. For example, if your list contains numbers and you only want numbers, you can use the filter method to only select a number that is fully divisible by two. The filter method, as its name suggests, filters elements based upon a condition you gave it. It is also an intermediate Stream operation, which means you can call other Stream methods, like a filter, or collect on this to create a chain of transformations. Then, the map() function will do the transformation for you. For example, by using the map() function, you can convert a list of String into a List of Integer by applying the Integer.valueOf() method to each String on the input list.Īll you need is a mapping function to convert one object to the other.
That's why the Stream.map(Function mapper) takes a function as an argument.
In simple words, the map() is used to transform one object into other by applying a function. The map() function is a method in the Stream class that represents a functional programming concept. Even though I have previously blogged about both the map() and filter(), I am writing again to expand on the concept in layman's language to provide even better understanding for everyone. Hello, guys! Many of my readers emailed me, asking to write a post about the map and filter function of Java 8, because they found it difficult to use and understand. Note: When you purchase through links on our site, we may receive an affiliate commission.
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