1. What is Java and why is it considered platform-independent?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong>
Java is a high-level, object-oriented programming language developed by Sun Microsystems (now owned by Oracle). It is considered platform-independent because Java code is compiled into bytecode<\/strong>, which can run on any device that has the Java Virtual Machine (JVM) installed, regardless of the underlying operating system.<\/p>\n\n\n\n2. What is the difference between JDK, JRE, and JVM?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong><\/p>\n\n\n\n\n- JDK (Java Development Kit):<\/strong> A software development kit that includes the compiler, debugger, and tools necessary to develop Java applications.<\/li>\n\n\n\n
- JRE (Java Runtime Environment):<\/strong> A package that provides the libraries and JVM required to run Java applications.<\/li>\n\n\n\n
- JVM (Java Virtual Machine):<\/strong> A virtual machine that executes Java bytecode and provides platform independence.<\/li>\n<\/ul>\n\n\n\n
3. What are the main features of Java?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong><\/p>\n\n\n\n\n- Object-Oriented<\/li>\n\n\n\n
- Platform Independent<\/li>\n\n\n\n
- Robust and Secure<\/li>\n\n\n\n
- Multithreaded<\/li>\n\n\n\n
- Automatic Memory Management (Garbage Collection)<\/li>\n\n\n\n
- Rich Standard Library<\/li>\n<\/ul>\n\n\n\n
4. What is the difference between ==<\/code> and .equals()<\/code> in Java?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong><\/p>\n\n\n\n\n==<\/code> compares references<\/strong> (i.e., whether two variables point to the same object in memory).<\/li>\n\n\n\n.equals()<\/code> compares content<\/strong> (i.e., whether two objects are logically equivalent).
For example, two different String<\/code> objects with the same value are equal using .equals()<\/code> but not with ==<\/code>.<\/li>\n<\/ul>\n\n\n\n5. What are Java’s primitive data types?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong>
Java has eight primitive data types:<\/p>\n\n\n\n\n- Integer types:<\/strong>
byte<\/code>, short<\/code>, int<\/code>, long<\/code><\/li>\n\n\n\n- Floating-point types:<\/strong>
float<\/code>, double<\/code><\/li>\n\n\n\n- Character type:<\/strong>
char<\/code><\/li>\n\n\n\n- Boolean type:<\/strong>
boolean<\/code><\/li>\n<\/ul>\n\n\n\n6. What are access modifiers in Java?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong>
Access modifiers define the scope of access to classes, methods, and variables. They are:<\/p>\n\n\n\n\npublic<\/code>: accessible from anywhere<\/li>\n\n\n\nprotected<\/code>: accessible within the same package or subclasses<\/li>\n\n\n\ndefault<\/code> (no modifier): accessible within the same package only<\/li>\n\n\n\nprivate<\/code>: accessible within the same class only<\/li>\n<\/ul>\n\n\n\n7. What is a constructor in Java?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong>
A constructor is a special method used to initialize objects. It has the same name as the class and does not have a return type. Java also supports constructor overloading<\/strong>, allowing multiple constructors with different parameter lists.<\/p>\n\n\n\n8. What is method overloading?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong>
Method overloading allows multiple methods with the same name but different parameters (type, number, or order) within the same class. It improves code readability and reusability.<\/p>\n\n\n\n9. What is the purpose of the main()<\/code> method in Java?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong>
The main()<\/code> method serves as the entry point for Java applications. Its standard signature is:<\/p>\n\n\n\njavaCopyEditpublic static void main(String[] args)<\/code><\/pre>\n\n\n\nThis method is executed by the JVM when the program starts.<\/p>\n\n\n\n
10. What is the difference between a class and an object?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong><\/p>\n\n\n\n\n- A class<\/strong> is a blueprint or template for creating objects.<\/li>\n\n\n\n
- An object<\/strong> is an instance of a class, representing a real-world entity with state and behavior.<\/li>\n<\/ul>\n\n\n\n
11. How do you define a constant in Java?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong>
Constants are defined using the final<\/code> keyword. For example:<\/p>\n\n\n\njavaCopyEditfinal int MAX_USERS = 100;\n<\/code><\/pre>\n\n\n\nOnce assigned, the value of a final variable cannot be changed.<\/p>\n\n\n\n
12. What is type casting in Java?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong>
Type casting is converting one data type into another.<\/p>\n\n\n\n\n- Implicit casting<\/strong> (widening): e.g.,
int<\/code> to long<\/code><\/li>\n\n\n\n- Explicit casting<\/strong> (narrowing): e.g.,
double<\/code> to int<\/code>
Example:<\/li>\n<\/ul>\n\n\n\njavaCopyEditint x = (int) 3.14;<\/code><\/pre>\n\n\n\n13. What is the use of the this<\/code> keyword in Java?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong>
this<\/code> refers to the current instance of the class. It is used to:<\/p>\n\n\n\n\n- Differentiate between instance variables and parameters<\/li>\n\n\n\n
- Invoke other constructors in the same class<\/li>\n\n\n\n
- Pass the current object as an argument<\/li>\n<\/ul>\n\n\n\n
14. What is the difference between break<\/code> and continue<\/code>?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong><\/p>\n\n\n\n\nbreak<\/code>: exits the current loop or switch statement.<\/li>\n\n\n\ncontinue<\/code>: skips the current iteration and moves to the next one within a loop.<\/li>\n<\/ul>\n\n\n\n15. What are wrapper classes in Java?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong>
Wrapper classes convert primitive types into objects. Examples include:<\/p>\n\n\n\n\nint<\/code> \u2192 Integer<\/code><\/li>\n\n\n\ndouble<\/code> \u2192 Double<\/code><\/li>\n\n\n\nboolean<\/code> \u2192 Boolean<\/code>
They are useful for working with collections (e.g., ArrayList<Integer><\/code>) that require object types.<\/li>\n<\/ul>\n\n\n\nIntermediate-Level Java Interview Questions (16\u201330)<\/h3>\n\n\n\n16. What is inheritance in Java?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong>
Inheritance is a core concept of object-oriented programming where one class (the subclass) inherits the fields and methods of another class (the superclass). It promotes code reuse<\/strong> and supports method overriding<\/strong> for extending or customizing behavior.<\/p>\n\n\n\n17. What is the difference between method overloading and method overriding?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong><\/p>\n\n\n\n\n- Method Overloading<\/strong>: Occurs within the same class. Methods have the same name but different parameter lists.<\/li>\n\n\n\n
- Method Overriding<\/strong>: Occurs in subclasses. A method in the child class has the same signature as in the parent class and provides a new implementation.<\/li>\n<\/ul>\n\n\n\n
18. What is an abstract class in Java?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong>
An abstract class cannot be instantiated. It may contain abstract methods (without implementation) as well as concrete methods. It serves as a base class for subclasses that must implement the abstract methods.<\/p>\n\n\n\n19. How is an interface different from an abstract class?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong><\/p>\n\n\n\n\n- Interfaces<\/strong> can only contain abstract methods (until Java 8, which introduced default and static methods). They provide pure abstraction<\/strong>.<\/li>\n\n\n\n
- Abstract classes<\/strong> can have both abstract and concrete methods and can also maintain state.
A class can implement multiple interfaces<\/strong> but only extend one class<\/strong>.<\/li>\n<\/ul>\n\n\n\n20. What is polymorphism in Java?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong>
Polymorphism allows one interface to be used for different underlying forms (types).<\/p>\n\n\n\n\n- Compile-time polymorphism<\/strong>: Achieved through method overloading<\/li>\n\n\n\n
- Runtime polymorphism<\/strong>: Achieved through method overriding and dynamic method dispatch<\/li>\n<\/ul>\n\n\n\n
21. What is encapsulation?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong>
Encapsulation is the practice of binding data and methods<\/strong> that operate on the data into a single unit (class). It is implemented using private fields<\/strong> and public getters\/setters<\/strong>, promoting data hiding and modularity.<\/p>\n\n\n\n22. What is the role of the super<\/code> keyword?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong>
The super<\/code> keyword refers to the parent class<\/strong>. It is used to:<\/p>\n\n\n\n\n- Call the superclass constructor<\/li>\n\n\n\n
- Access superclass methods and variables hidden by the subclass<\/li>\n<\/ul>\n\n\n\n
23. What is the final<\/code> keyword used for?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong>
The final<\/code> keyword can be used with:<\/p>\n\n\n\n\n- Variables<\/strong>: Value cannot be changed after initialization<\/li>\n\n\n\n
- Methods<\/strong>: Cannot be overridden<\/li>\n\n\n\n
- Classes<\/strong>: Cannot be subclassed<\/li>\n<\/ul>\n\n\n\n
24. What is exception handling in Java?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong>
Exception handling in Java allows you to manage runtime errors using try<\/code>, catch<\/code>, finally<\/code>, and throw<\/code> statements. It ensures graceful error recovery and program stability.<\/p>\n\n\n\n25. What is the difference between checked and unchecked exceptions?<\/strong><\/h4>\n\n\n\nAnswer:<\/strong><\/p>\n\n\n\n\n- Checked exceptions<\/strong>: Must be handled using
try-catch<\/code> or declared in the method signature. Examples: IOException<\/code>, SQLException<\/code>.<\/li>\n\n\n\n- Unchecked exceptions<\/strong>: Subclasses of
RuntimeException<\/code>; do not need explicit handling. Examples: NullPointerException<\/code>, ArrayIndexOutOfBoundsException<\/code>.<\/li>\n<\/ul>\n\n\n\n26. What is the Java Collections Framework?<\/strong><\/h4>\n\n\n\n