Head First Java, 3rd Edition

Chapter 12. Lambdas and Streams: What, Not How: Lambdas and Streams

What if...you didn’t need to tell the computer HOW to do something? Programming involves a lot of telling the computer how to do something: while this is true do this thing; for all these items if it looks like this then do this; and so on.

We’ve also seen that we don’t have to do everything ourselves. The JDK contains library code, like the Collections API we saw in the previous chapter, that we can use instead of writing everything from scratch. This library code isn’t just limited to collections to put data into; there are methods that will do common tasks for us, so we just need to tell them what we want and not how to do it.

In this chapter we’ll look at the Streams API. You’ll see how helpful lambda expressions can be when you’re using streams, and you’ll learn how to use the Streams API to query and transform the data in a collection.

Tell the computer WHAT you want

Imagine you have a list of colors, and you wanted to print out all the colors. You could use a for loop to do this.

But doing something to every item in a list is a really common thing to want to do. So instead of creating a for loop every time we want to do something “for each” item in the list, we can call the forEach ...