Core Java Fundamentals Interview Questions

Java provides platform independence, object-oriented programming, robustness, security, multithreading, distributed computing support, automatic memory management, and high performance through JIT compilation.

Java is platform independent because Java source code is compiled into bytecode, which can run on any operating system that has a compatible JVM installed.

JVM (Java Virtual Machine) is a runtime environment that executes Java bytecode. It provides platform independence and manages memory, garbage collection, and execution.

JRE (Java Runtime Environment) contains the JVM and required libraries needed to run Java applications but does not include development tools.

JDK (Java Development Kit) includes JRE along with development tools such as javac, java, javadoc, and debugger utilities required to develop Java applications.

Java source code is compiled by javac into bytecode. The JVM loads the bytecode, verifies it, and executes it using the interpreter and JIT compiler.

Java is platform independent, supports automatic garbage collection, and does not support multiple inheritance through classes, whereas C++ is platform dependent and provides manual memory management.

Java has eight primitive data types: byte, short, int, long, float, double, char, and boolean.

Type casting is the process of converting a value from one data type to another. It can be implicit or explicit.

Implicit casting is performed automatically when converting a smaller type to a larger type, while explicit casting requires manual conversion from a larger type to a smaller type.

Operators are symbols used to perform operations on variables and values. Examples include arithmetic, relational, logical, assignment, bitwise, and ternary operators.

The == operator compares object references, while equals() compares object content when properly overridden.

Command-line arguments are values passed to a Java program through the main method parameter String[] args during execution.

Unicode is a universal character encoding standard used by Java to support internationalization and represent characters from multiple languages.

Bytecode is the intermediate code generated by the Java compiler. It is platform independent and executed by the JVM.

Name concrete APIs (collections, concurrency, streams, annotations) tied to Core Java Fundamentals. Interviewers want syntax-level clarity plus when you would reach for each feature in production.

Prefer specific checked/unchecked exceptions, wrap lower-level failures with context, and avoid empty catch blocks. For Core Java Fundamentals, decide what is recoverable vs fatal to the request thread.

JUnit 5 with Arrange-Act-Assert, Mockito for collaborators, and parameterized tests for edge cases. Keep Core Java Fundamentals logic pure where possible so tests stay fast.

Incorrect equals/hashCode break HashMap/HashSet behavior. If Core Java Fundamentals stores objects in collections, explain the contract and mutability pitfalls.

Retain only needed references, prefer streaming for large datasets, and avoid accidental caches. Relate leaks or GC pressure to a concrete Core Java Fundamentals scenario.