Tutorials & Books
https://refactoring.guru/design-patterns
https://sourcemaking.com/design_patterns
https://www.amazon.com/Head-First-Design-Patterns-Object-Oriented-dp-149207800X/dp/149207800X
https://www.amazon.com/Java-Design-Patterns-Hands-Experience/dp/1484240774
https://www.journaldev.com/java/design-patterns
https://www.udemy.com/course/design-patterns-in-java-concepts-hands-on-projects/