Inf1-OP Bonus Lecture - JUnit, Lambdas and Streams Volker Seeker - PowerPoint PPT Presentation

Inf1-OP Bonus Lecture - JUnit, Lambdas and Streams Volker Seeker School of Informatics March 20, 2019

Automatic Testing with JUnit

Test Driven Development Source: https://dzone.com/articles/what-is-refactoring

Simple Calculator Calculator +add(int, int):int +mul(int, int):int +incrementAll(int[], int):void Implement a utility class with calculator functionality.

How would you test the functionality of a class? Demo

Main Method as Test Client Main methods can be used to quickly evaluate the functionality of your code.

Main Method as Test Client Main methods can be used to quickly evaluate the functionality of your code. They have, however, a few drawbacks:

Main Method as Test Client Main methods can be used to quickly evaluate the functionality of your code. They have, however, a few drawbacks: ◮ Using console output to evaluate test results requires manual effort and is error prone for more complex tests

Main Method as Test Client Main methods can be used to quickly evaluate the functionality of your code. They have, however, a few drawbacks: ◮ Using console output to evaluate test results requires manual effort and is error prone for more complex tests → use assertions instead!

Automatic evaluation with assertions Demo

Main Method as Test Client Main methods can be used to quickly evaluate the functionality of your code. They have, however, a few drawbacks: ◮ Using console output to evaluate test results requires manual effort and is error prone for more complex tests → use assertions instead!

Main Method as Test Client Main methods can be used to quickly evaluate the functionality of your code. They have, however, a few drawbacks: ◮ Using console output to evaluate test results requires manual effort and is error prone for more complex tests → use assertions instead! ◮ tests are unorganised, no easy way to test only certain methods

Main Method as Test Client Main methods can be used to quickly evaluate the functionality of your code. They have, however, a few drawbacks: ◮ Using console output to evaluate test results requires manual effort and is error prone for more complex tests → use assertions instead! ◮ tests are unorganised, no easy way to test only certain methods → use a test framework instead!

Organising Tests with a Test Framework Demo

Summary Automatic Testing with JUnit ◮ Tests results are evaluated automatically

Summary Automatic Testing with JUnit ◮ Tests results are evaluated automatically ◮ Tests are organised in a standard way

Summary Automatic Testing with JUnit ◮ Tests results are evaluated automatically ◮ Tests are organised in a standard way ◮ Tests can be executed in isolation for only specific features

Summary Automatic Testing with JUnit ◮ Tests results are evaluated automatically ◮ Tests are organised in a standard way ◮ Tests can be executed in isolation for only specific features ◮ Tests can easily be excluded from shipped product

Summary Automatic Testing with JUnit ◮ Tests results are evaluated automatically ◮ Tests are organised in a standard way ◮ Tests can be executed in isolation for only specific features ◮ Tests can easily be excluded from shipped product ◮ Framework functionality provides advanced capabilities

Summary Automatic Testing with JUnit ◮ Tests results are evaluated automatically ◮ Tests are organised in a standard way ◮ Tests can be executed in isolation for only specific features ◮ Tests can easily be excluded from shipped product ◮ Framework functionality provides advanced capabilities ◮ @Before or @After methods are executed before and after each test to setup and clean up the test environment

Summary Automatic Testing with JUnit ◮ Tests results are evaluated automatically ◮ Tests are organised in a standard way ◮ Tests can be executed in isolation for only specific features ◮ Tests can easily be excluded from shipped product ◮ Framework functionality provides advanced capabilities ◮ @Before or @After methods are executed before and after each test to setup and clean up the test environment ◮ @Test(timeout = 1000) allows testing for execution duration

Summary Automatic Testing with JUnit ◮ Tests results are evaluated automatically ◮ Tests are organised in a standard way ◮ Tests can be executed in isolation for only specific features ◮ Tests can easily be excluded from shipped product ◮ Framework functionality provides advanced capabilities ◮ @Before or @After methods are executed before and after each test to setup and clean up the test environment ◮ @Test(timeout = 1000) allows testing for execution duration ◮ etc.

ArrayLists and Hashtables Recap

Lists Demo

Maps Demo

Lambdas

Filter a list of numbers by a threshold Demo

Filtering a List The Predicate interface specifies an API which classes can implement to provide filter functionality.

Filtering a List The Predicate interface specifies an API which classes can implement to provide filter functionality. However, writing a new class for each new filter is inconvenient.

Filtering a List The Predicate interface specifies an API which classes can implement to provide filter functionality. However, writing a new class for each new filter is inconvenient. Let’s make this easier by using an Anonymous class!.

Filter a list of numbers by a threshold with an Anonymous class Demo

Filtering a List The Predicate interface specifies an API which classes can implement to provide filter functionality. However, writing a new class for each new filter is inconvenient. Let’s make this easier by using an Anonymous class!. Anonymous classes help, but we can do better.

Filtering a List The Predicate interface specifies an API which classes can implement to provide filter functionality. However, writing a new class for each new filter is inconvenient. Let’s make this easier by using an Anonymous class!. Anonymous classes help, but we can do better. Let’s use an anonymous function, i.e. a Lambda expression!

Filter a list of numbers by a threshold with a Lambda expression Demo

Summary Lambda expressions in Java ◮ A lambda expression is an anonymous function

Summary Lambda expressions in Java ◮ A lambda expression is an anonymous function ◮ It can be called without an explicit identifier, i.e. method name

Summary Lambda expressions in Java ◮ A lambda expression is an anonymous function ◮ It can be called without an explicit identifier, i.e. method name ◮ This makes it easy to pass them around as method arguments

Summary Lambda expressions in Java ◮ A lambda expression is an anonymous function ◮ It can be called without an explicit identifier, i.e. method name ◮ This makes it easy to pass them around as method arguments ◮ They can be used in place of any Functional Interface such as Predicate

Summary Lambda expressions in Java ◮ A lambda expression is an anonymous function ◮ It can be called without an explicit identifier, i.e. method name ◮ This makes it easy to pass them around as method arguments ◮ They can be used in place of any Functional Interface such as Predicate ◮ An interface with only a single abstract method

Summary Lambda expressions in Java ◮ A lambda expression is an anonymous function ◮ It can be called without an explicit identifier, i.e. method name ◮ This makes it easy to pass them around as method arguments ◮ They can be used in place of any Functional Interface such as Predicate ◮ An interface with only a single abstract method ◮ see java.util.function package for a large collection of available options

Streams

Streams A stream ◮ represents a sequence of elements ◮ supports different kinds of operations This is where lambda expressions become very handy.

Performing computations using Java streams. Demo

Extensive Stream Tutorial: https://winterbe.com/posts/2014/07/31/ java8-stream-tutorial-examples/

Questions?