Core Packages, Collections, Streams, OOP & Ready-to-Compile Examples
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Java runs on the JVM — the same bytecode runs on Linux, Windows, macOS, Android, and embedded systems without recompilation.
Spring Boot, Hibernate, Jakarta EE — Java powers the backend of banks, governments, and Fortune 500 companies worldwide.
Java (and Kotlin, which runs on the JVM) is the primary language for Android apps — 3 billion+ devices run Java-based code.
Java teaches strict object-oriented design — classes, interfaces, inheritance, polymorphism — concepts that transfer to every other language.
Java requires the filename to match the public class name:
javac Hello.java # compile — produces Hello.class java Hello # run class (no .class extension) javac *.java # compile all .java files java -cp . Hello # explicitly set classpath jar cf app.jar *.class # package into JAR java -jar app.jar # run JAR file java --version # check installed Java version javadoc Hello.java -d docs/ # generate HTML documentation
