Java
Object-oriented programming and the Spring ecosystem behind much of enterprise software.
Beginner
Start here. No background needed beyond school maths.
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Beginner
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Learn Java (dev.java)
••••'s official, regularly updated learning hub for Java: language basics, the standard library, tools and newer language features.
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Beginner
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The Java Tutorials
The long-running official tutorial trail: classes, generics, collections, concurrency and I/O, written by the Java team.
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Advanced
Once the basics are comfortable.