Java – Interview Questions
Explore a curated collection of Java interview questions covering a wide range of topics and difficulty levels—from beginner to advanced. Whether you’re just starting out or preparing for senior-level interviews, this page helps you practice effectively with clear questions, concise answers, and in-depth explanations.
Use the filter to quickly find questions by level and focus on the areas that matter most to you. Each question is designed to reinforce key concepts, improve your problem-solving skills, and prepare you for real-world technical interviews.
Start practicing, test your knowledge, and get interview-ready with structured, high-quality Java questions.
What are the limitations of JShell?
JShell is great for quick experiments, but it is less suitable for large applications, complex project structures, build automation, and scenarios that need full IDE support or application lifecycle setup.
Why is setting JAVA_HOME important?
Setting JAVA_HOME provides a standard environment variable that points to the installed JDK or Java installation. Many tools use it to locate Java consistently.
What is bytecode in Java?
Bytecode is the intermediate instruction format produced by the Java compiler. It is executed by the JVM.
What is the difference between javac and java commands?
javac compiles Java source code into bytecode. java runs the compiled bytecode on the JVM.
What is a breakpoint in debugging?
A breakpoint is a marker that tells the debugger to pause execution at a specific line so you can inspect variables, flow, and program state.
What is debugging and why is it important?
Debugging is the process of inspecting and tracing a program to find and fix problems. It is important because it helps understand program behavior and identify the cause of bugs more efficiently.
What is JShell and when should you use it?
JShell is Java's interactive REPL tool. Use it for quick experiments, learning, testing small code snippets, and exploring APIs without creating a full project.
What is the role of the project SDK in IntelliJ IDEA?
The project SDK tells IntelliJ IDEA which JDK to use for compiling, running, and providing language features for the project.
What are the main steps to create and run a Java application in an IDE?
The main steps are to create a project, configure the JDK, add source files, write the code, build the project, and run the application from the IDE.
What is the difference between JDK, JRE, and JVM?
The JVM runs Java bytecode. The JRE provides the JVM plus the libraries needed to run Java applications. The JDK includes the JRE plus development tools such as the compiler.
What is the purpose of the main method in Java?
The main method is the standard entry point where the JVM starts executing a standalone Java application.
Can a Java program run without a main method?
Yes, a Java program can run without a main method in some contexts, such as when launched by a framework, a servlet container, tests, or certain tools. But a standard standalone Java application normally needs one as its entry point.
Why must the main method be static in Java?
The main method must be static so the JVM can call it without creating an object first. It serves as the entry point of the program.
What are arithmetic operators in Java?
The main arithmetic operators in Java are +, -, *, /, %, ++, and --.
What is operator precedence in Java?
Operator precedence defines the order in which operators are evaluated in an expression when there are no parentheses.
What are operators in Java?
Operators are symbols used to perform operations on values and variables, such as arithmetic, comparison, assignment, and logical operations.
What is the difference between int and Integer?
int is a primitive type that stores a 32-bit integer value. Integer is the wrapper class that represents an int as an object and can be used where objects are required.
What are primitive data types in Java?
Java has eight primitive data types: byte, short, int, long, float, double, char, and boolean.
What is the difference between switch statement and switch expression?
A switch statement controls execution flow, while a switch expression produces a value that can be assigned or returned.
What are the advantages of switch expressions over traditional switch?
Switch expressions are more concise, avoid accidental fall-through by default, and can directly return a value, which makes code clearer and safer.