Mutability Detector: Analysis Tool for Detecting Mutability in Java

What is Mutability Detector?

Mutability Detector is designed to analyse Java classes and report on whether instances of a given class are immutable. It can be used:

  • In a unit test, with an assertion like assertImmutable(MyClass.class). Is your class actually immutable? What about after that change you just made?
  • As a FindBugs plugin. Those classes you annotated with @Immutable, are they actually?
  • At runtime. Does your API require being given immutable objects?
  • From the command line. Do you want to quickly run Mutability Detector over an entire code base?

Why Try To Detect Mutability?

Developing classes to be immutable has several benefits. An immutable object is one which cannot be changed once it is constructed. While writing concurrent programs, using immutable objects can greatly simplify complex systems, as sharing an object across threads is much safer. There are a few rules for what makes an object immutable, and it is easy to break the rules and render the object unsafe. This could lead to subtle, hard-to-detect bugs which could lower the integrity of the system. Using an automated tool to recognise mutability where it's not intended can reduce the complexity of writing immutable classes.

Mutability Detector analyses on the strict side, very few classes are found to be perfectly immutable, for instance, java.lang.String and java.lang.Integer are not immutable because of a non-final field, and primitive array field, respectively. Mutability Detector will not be released under a 1.0 version until these cases can be correctly analysed.

If this sounds like it may be interesting or useful to you, continue reading for more information on getting started. You may also want to take a look at the Mutability Detector Blog.

Getting Started

To use Mutability Detector directly, either from the command line, at runtime in your application, or as part of your unit tests, grab the jar available from Maven Central. Or you can declare it in your Maven-compatible build tool, with the following coordinates:

    <version>[latest version here]</version>

Using Mutability Detector in Unit Testing

Just add MutabilityDetector to your unit testing classpath. Adding your first assertion is as simple as:

import static org.mutabilitydetector.unittesting.MutabilityAssert.assertImmutable;

@Test public void checkMyClassIsImmutable() {

Though it is possible (or likely) that you will have to configure the assertion to deal with any false positives that arise. See the JavaDoc on MutabilityAssert for further information.

Using Mutability Detector from the Command Line

An example of how to run it is probably the most useful. If you want to analyse MyCodebase.jar use:

java -jar MutabilityDetector.jar -classpath path/to/MyCodebase.jar

Mutability Detector can handle jars as seen above, or directories of class files (thanks go to the authors of classpath-explorer). So if your codebase was in the filesystem as directories and .class files, and the directory MyCodebase was the root of that, you could run:

java -jar MutabilityDetector.jar -classpath path/to/MyCodebase

The output is a list of the analysed classes against the result of asking "Is immutable?", ie. IMMUTABLE, NOT_IMMUTABLE, EFFECTIVELY_IMMUTABLE.

Execute java -jar MutabilityDetector.jar --help for a complete listing of the command line options.

Using Mutability Detector within Your Application

It is possible to use Mutability Detector at runtime. For example, consider if you have a library which requires that objects passed to it are immutable. On receiving such an object, you can ask Mutability Detector if it is actually immutable.

Check out the code snippet in this example, which shows correct usage against trunk code.

FindBugs Plugin

To have Mutability Detector inspect your classes during a FindBugs analysis, grab the MutabilityDetector4FindBugs jar, and configure it to be picked up by FindBugs during a normal analysis, as described here.

Mutability Detector will perform it's analysis on any classes annotated with @Immutable.

MutabilityDetector4FindBugs is also available from Maven Central, with the following coordinates:

    <version>[latest version here]</version>

Download details:

Author: MutabilityDetector
Source code:
License: Apache-2.0 license

#java #testing

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Mutability Detector: Analysis Tool for Detecting Mutability in Java
Tyrique  Littel

Tyrique Littel


How to Install OpenJDK 11 on CentOS 8

What is OpenJDK?

OpenJDk or Open Java Development Kit is a free, open-source framework of the Java Platform, Standard Edition (or Java SE). It contains the virtual machine, the Java Class Library, and the Java compiler. The difference between the Oracle OpenJDK and Oracle JDK is that OpenJDK is a source code reference point for the open-source model. Simultaneously, the Oracle JDK is a continuation or advanced model of the OpenJDK, which is not open source and requires a license to use.

In this article, we will be installing OpenJDK on Centos 8.

#tutorials #alternatives #centos #centos 8 #configuration #dnf #frameworks #java #java development kit #java ee #java environment variables #java framework #java jdk #java jre #java platform #java sdk #java se #jdk #jre #open java development kit #open source #openjdk #openjdk 11 #openjdk 8 #openjdk runtime environment

Samanta  Moore

Samanta Moore


Going Beyond Java 8: Local Variable Type Inference (var) - DZone Java

According to some surveys, such as JetBrains’s great survey, Java 8 is currently the most used version of Java, despite being a 2014 release.

What you are reading is one in a series of articles titled ‘Going beyond Java 8,’ inspired by the contents of my book, Java for Aliens. These articles will guide you step-by-step through the most important features introduced to the language, starting from version 9. The aim is to make you aware of how important it is to move forward from Java 8, explaining the enormous advantages that the latest versions of the language offer.

In this article, we will talk about the most important new feature introduced with Java 10. Officially called local variable type inference, this feature is better known as the **introduction of the word **var. Despite the complicated name, it is actually quite a simple feature to use. However, some observations need to be made before we can see the impact that the introduction of the word var has on other pre-existing characteristics.

#java #java 11 #java 10 #java 12 #var #java 14 #java 13 #java 15 #verbosity

Samanta  Moore

Samanta Moore


Guidelines for Java Code Reviews

Get a jump-start on your next code review session with this list.

Having another pair of eyes scan your code is always useful and helps you spot mistakes before you break production. You need not be an expert to review someone’s code. Some experience with the programming language and a review checklist should help you get started. We’ve put together a list of things you should keep in mind when you’re reviewing Java code. Read on!

1. Follow Java Code Conventions

2. Replace Imperative Code With Lambdas and Streams

3. Beware of the NullPointerException

4. Directly Assigning References From Client Code to a Field

5. Handle Exceptions With Care

#java #code quality #java tutorial #code analysis #code reviews #code review tips #code analysis tools #java tutorial for beginners #java code review

Samanta  Moore

Samanta Moore


Spring Boot and Java 16 Records

In this article, we will discuss Java 16’s newest feature, Records. Then we will apply this knowledge and use it in conjunction with a Spring Boot application.

On March 16th, 2021, Java 16 was GA. With this new release, tons of new exciting features have been added. Check out the release notes to know more about these changes in detail. This article’s focus will be on Java Records, which got delivered with JEP 395. Records were first introduced in JDK 14 as a preview feature proposed by JEP 359, and with JDK 15, they remained in preview with JEP 384. However, with JDK 16, Records are no longer in preview.

I have picked Records because they are definitely the most favored feature added in Java 16, according to this Twitter poll by Java Champion Mala Gupta.

I also conducted a similar survey, but it was focused on features from Java 8 onwards. The results were not unexpected, as Java 8 is still widely used. Very unfortunate, though, as tons of new features and improvements are added to newer Java versions. But in terms of features, Java 8 was definitely a game-changer from a developer perspective.

So let’s discuss what the fuss is about Java Records.

#java #springboot #java programming #records #java tutorials #java programmer #java records #java 16

Tyrique  Littel

Tyrique Littel


Static Code Analysis: What It Is? How to Use It?

Static code analysis refers to the technique of approximating the runtime behavior of a program. In other words, it is the process of predicting the output of a program without actually executing it.

Lately, however, the term “Static Code Analysis” is more commonly used to refer to one of the applications of this technique rather than the technique itself — program comprehension — understanding the program and detecting issues in it (anything from syntax errors to type mismatches, performance hogs likely bugs, security loopholes, etc.). This is the usage we’d be referring to throughout this post.

“The refinement of techniques for the prompt discovery of error serves as well as any other as a hallmark of what we mean by science.”

  • J. Robert Oppenheimer


We cover a lot of ground in this post. The aim is to build an understanding of static code analysis and to equip you with the basic theory, and the right tools so that you can write analyzers on your own.

We start our journey with laying down the essential parts of the pipeline which a compiler follows to understand what a piece of code does. We learn where to tap points in this pipeline to plug in our analyzers and extract meaningful information. In the latter half, we get our feet wet, and write four such static analyzers, completely from scratch, in Python.

Note that although the ideas here are discussed in light of Python, static code analyzers across all programming languages are carved out along similar lines. We chose Python because of the availability of an easy to use ast module, and wide adoption of the language itself.

How does it all work?

Before a computer can finally “understand” and execute a piece of code, it goes through a series of complicated transformations:

static analysis workflow

As you can see in the diagram (go ahead, zoom it!), the static analyzers feed on the output of these stages. To be able to better understand the static analysis techniques, let’s look at each of these steps in some more detail:


The first thing that a compiler does when trying to understand a piece of code is to break it down into smaller chunks, also known as tokens. Tokens are akin to what words are in a language.

A token might consist of either a single character, like (, or literals (like integers, strings, e.g., 7Bob, etc.), or reserved keywords of that language (e.g, def in Python). Characters which do not contribute towards the semantics of a program, like trailing whitespace, comments, etc. are often discarded by the scanner.

Python provides the tokenize module in its standard library to let you play around with tokens:



import io


import tokenize



code = b"color = input('Enter your favourite color: ')"



for token in tokenize.tokenize(io.BytesIO(code).readline):





TokenInfo(type=62 (ENCODING),  string='utf-8')


TokenInfo(type=1  (NAME),      string='color')


TokenInfo(type=54 (OP),        string='=')


TokenInfo(type=1  (NAME),      string='input')


TokenInfo(type=54 (OP),        string='(')


TokenInfo(type=3  (STRING),    string="'Enter your favourite color: '")


TokenInfo(type=54 (OP),        string=')')


TokenInfo(type=4  (NEWLINE),   string='')


TokenInfo(type=0  (ENDMARKER), string='')

(Note that for the sake of readability, I’ve omitted a few columns from the result above — metadata like starting index, ending index, a copy of the line on which a token occurs, etc.)

#code quality #code review #static analysis #static code analysis #code analysis #static analysis tools #code review tips #static code analyzer #static code analysis tool #static analyzer