Java 8 Lambdas Hands-on Lab Materials
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Oracle Code One Lambda Programming Laboratory


Welcome to the Lambda Programming Laboratory! The goal of this lab is for you to learn about the lambda expressions, default methods, and APIs (particularly the Streams library) introduced in Java 8, plus a few API additions in Java 9 and 10.

The lab is structured as a set of exercises in the form of JUnit tests. To complete each exercise, write some code that uses a lambda or new API that enables the test to pass.

Lab Instructions

  1. Open the NetBeans development build (or your favorite IDE).

  2. Open the LambdaLab project. If you don't have it, it can be cloned from github:

    git clone

  3. Inside the LambdaLab project, open the Test Packages folder.

  4. Open up one of the following exercise files:
  5. Each exercise is in the form of a single JUnit test method. Each test is marked with an @Ignore annotation so that JUnit will skip that test initially.

  6. To work on a test, delete the @Ignore annotation, fill in code at the // TODO marker, trying to avoid modifying any setup code above the TODO marker and assertion code below the TODO marker.

  7. Press Control-F6 to run the tests in this file.

  8. Make all the tests pass and get a 100% green bar!

Detailed Test Description

At the top of each exercise is a comment that describes the goal of the exercise. Within the test method, there is a // TODO comment that marks the location where you need fill in some implementation code. There may be some setup code above the // TODO comment, and there will be some assertion-checking code below. You shouldn't have to modify any of the setup code at the top of the test method or the assertions at the bottom of the test method.

There is sometimes a hint or two after a test method. If you're having trouble with an exercise, look for hints. The hint text is inside a editor fold that is closed by default, so click on the plus-sign in the left margin to read it.

The intent of the exercises is to solve them using the Java 8 lambda expressions feature, the Java 8 default methods feature, the Java 8 Streams API, and other APIs added in Java 8 or Java 9. Of course, it is possible to use conventional Java code, such as for-loops, but all of the exercises are amenable to being solved using new features in just a handful of lines. Most exercises will take less than half a dozen lines. Some of the more difficult exercises may take up to eight lines, depending upon how aggressive you are about breaking lines. None of the exercises involve writing large amounts of code. Most of the streams-based exercises involve writing a single stream pipeline.

Several of the exercises read data from a text file. The field named "reader" is a BufferedReader which will be opened for you on the text file. In any exercise that refers to reading from the text file, you can simply use the "reader" variable without worry about opening or closing it. This is set up by JUnit using the @Before and @After methods at the bottom of the file. The text file is "SonnetI.txt" (Shakespeare's first sonnet) which is located at the root of this NetBeans project.

If you're really stuck, the solutions to the exercises are in the package

    Test Packages > solutions

There is one solutions file corresponding to each exercise file. Many exercises can be solved in several different ways. In some cases, the solutions file will have several alternatives. Even if you've solved an exercise, it can be useful to look at the solutions to compare your solutions with those of the lab authors.