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

+mul(int, int):int +add(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

• ptions

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?