How can you write simple and performant equals() methods for your Java classes: the full tutorial.
Usually you do not write your equals() and hashCode() methods yourself. You delegate that to your IDE and forget about it. This JEP Café deep dives into the different solutions offered by Eclipse and IntelliJ, as well as Guava and Apache Commons Lang 3. It compares these solutions and checks the performance they offer on various real-life use cases. It also compares them with the Pattern Matching solution, available from Java 17 and Java 21.
⎯⎯⎯⎯⎯⎯ Chapters ⎯⎯⎯⎯⎯⎯
0:00 Intro: designing equals() methods
1:13 Generating equals() and hashCode() methods
1:56 What could go wrong with a bad hashCode() method
4:31 Taking a look at the generated equals() methods
7:11 Checking the record and pattern matching implementations
9:33 What is predictive branching, what is the cost of a failing prediction?
12:41 Evaluating the cost of two failing predictions.
14:53 Evaluating the performance of equals() methods on simple data sets
16:07 First data set: all the objects are the same instance
16:46 Second data set: different instances carrying the same state
18:43 Third data set: different objects of the same type
20:41 Fourth data set: objects of different types
22:00 First conclusions on what patterns are the best
22:39 Adding glitches to the data sets
24:41 Results for first data set (same instances) with glitches
25:20 Results for second data set (equal instances) with glitches
26:07 Results for third data set (different instances) with glitches
28:30 Results for fourth data set (different types) with glitches
30:05 What conclusions can you draw from all these benches?
32:33 That's it for today, talk to you soon!
⎯⎯⎯⎯⎯⎯ Resources ⎯⎯⎯⎯⎯⎯
◦ Pattern Matching for intanceof ➱ https://openjdk.org/jeps/394
◦ Records ➱ https://openjdk.org/jeps/395
◦ Record Patterns ➱ https://openjdk.org/jeps/440
◦ Guava ➱ https://guava.dev/
◦ Apache Commons Lang 3 ➱ https://commons.apache.org/proper/commons-lang/
◦ Eclipse IDE ➱ https://www.eclipse.org/ide/
◦ IntelliJ IDE ➱ https://www.jetbrains.com/idea/
◦ JMH on GitHub, with doc and samples ➱ https://github.com/openjdk/jmh
◦ Alexey Shipilev on JMH ➱ https://youtu.be/VaWgOCDBxYw
◦ Dev.java ➱ https://dev.java
◦ Inside.java ➱ https://inside.java
◦ JDK 21 ➱ https://openjdk.org/projects/jdk/21
◦ JDK 17 ➱ https://openjdk.org/projects/jdk/17
◦ OpenJDK ➱ https://openjdk.org
◦ Oracle Java ➱ https://www.oracle.com/java/
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