Study Guide to Java Core Concepts and OOP: 73 Flashcards from the JVM to Polymorphism

Java interviews and university exams rarely ask you to write a full program; they ask whether you know the rules. Can a constructor return a value? Can a static method touch an instance variable? Which garbage collector is the default since Java 9? The Java: Core Concepts & OOP deck on Flip It (deck code ZF8208, 73 cards) is built exactly around those rules — the platform, the memory model and the four pillars of object-oriented programming.

Sample cards

What the 73 cards cover

• Platform: Java bytecode, JVM, JRE vs JDK, OpenJDK, HotSpot and tiered compilation, Jazelle, the original interactive-TV design goal, the five primary design goals, the four editions (Java Card, ME, SE, EE).
• Type system and memory: static/strong/nominative/manifest typing, primitives vs objects, no pointer arithmetic, no operator overloading, automatic garbage collection, logical memory leaks, NullPointerException.
• OOP pillars: class, object, inheritance, interface, encapsulation, polymorphism, method overriding vs overloading, abstract class vs interface, constructor, this, super, new, static methods and variables, final class/method/variable, the four access modifiers (public, private, protected, package-private).
• Ecosystem: Javadoc and the three comment styles, public static void main(String[] args), applets (deprecated in Java 9), servlets, JSP, Swing, JavaFX, JDBC, the Collections Framework, reflection, try-catch-finally, checked vs unchecked exceptions, Android's relationship to Java.

Study tips specific to Java

Learn the "No" cards as a family. A striking number of cards in this deck have a one-word answer: No. No operator overloading, no multiple class inheritance, no pointer arithmetic, no return type on constructors, no instance access from static methods, no guaranteed manual GC. Each no is a deliberate design decision for safety or performance — memorise the reason on the back (e.g. no pointer arithmetic so the garbage collector can relocate objects) and the rule becomes obvious instead of arbitrary.

Pair every OOP term with its keyword. The deck's OOP cards map almost one-to-one onto keywords: inheritance ↔ extends, interface ↔ implements, encapsulation ↔ private + getters, overriding ↔ @Override, constant ↔ final, class-level ↔ static. When you flip a definition card, say the keyword out loud before revealing the answer; it doubles your recall cues.

Suggested order

1. Platform cards first (bytecode → JVM → JRE/JDK → garbage collectors): pure facts, a quick warm-up.
2. OOP pillars with an editor open — write a three-line abstract class while reviewing the abstract-class cards.
3. Ecosystem and exceptions last: servlets, JSP, Swing, JavaFX are recognition-level knowledge.

Log in at flip-it.app, find deck ZF8208 — Java: Core Concepts & OOP in the library, and let spaced repetition schedule the G1GC card for you until it stops feeling like trivia.

If you are new to the method, our practical guide to learning with flashcards explains how the review intervals work.