Java Programming Syllabus

What does the modulo operator % return, and evaluate $17 \% 5$.

It returns the remainder of integer division. $17 \% 5 = 2$.

Explain the ternary operator with its syntax.

Shorthand for if-else: condition ? valueIfTrue : valueIfFalse. Example: int max = (a > b) ? a : b;

What is the difference between the logical operators & and && (and | vs ||)?

&& and || are short-circuit: they skip evaluating the right operand if the result is already determined. & and | always evaluate both operands (non-short-circuit).

Differentiate prefix (++i) and postfix (i++) increment.

Prefix ++i increments first, then returns the new value. Postfix i++ returns the current value, then increments. If i=5: int a=++i gives a=6; int b=i++ gives b=5 (then i=6).

Name the looping control statements in Java.

for loop, enhanced for-each loop, while loop, and do-while loop.

What is the key difference between a while loop and a do-while loop?

while checks the condition before executing the body (may run 0 times). do-while executes the body once before checking the condition (always runs at least once).

What is the difference between break and continue?

break exits the entire loop/switch immediately. continue skips the rest of the current iteration and proceeds to the next iteration.

In a switch statement, what is the role of break and default?

break terminates the switch to prevent "fall-through" into subsequent cases. default is the block executed when no case matches the value.

Define a class and an object in Java.

A class is a blueprint/template defining state (fields) and behavior (methods). An object is a concrete instance of a class, created with the new keyword and occupying memory.

What is a constructor and how does it differ from a method?

A constructor initializes a new object; it has the same name as the class, has no return type, and is called automatically with new. Unlike methods, it cannot be invoked explicitly later or return a value.

What does the this keyword refer to?

this refers to the current object instance. It is used to access instance members, disambiguate shadowed fields, or call another constructor (this(...)).

Define the four pillars of Object-Oriented Programming.

Encapsulation (bundling data + methods, hiding internals), Inheritance (deriving classes from others), Polymorphism (one interface, many forms), and Abstraction (exposing essentials, hiding details).

What is inheritance and which keyword implements it in Java?

Inheritance lets a subclass acquire fields and methods of a superclass, promoting code reuse. It is implemented with the extends keyword (and implements for interfaces).

Does Java support multiple inheritance of classes? How is the limitation addressed?

No—Java does not allow a class to extend multiple classes (to avoid the "diamond problem"). Multiple inheritance of type is achieved by implementing multiple interfaces.

What does the super keyword do?

super refers to the immediate parent class: it calls the parent constructor (super(...)) or accesses parent class methods/fields that are overridden or hidden.

Differentiate method overloading and method overriding.

Overloading: same method name, different parameter lists, within the same class (compile-time/static polymorphism). Overriding: subclass redefines a superclass method with the same signature (runtime/dynamic polymorphism).

What is the difference between compile-time and runtime polymorphism?

Compile-time (static) polymorphism is achieved via method overloading, resolved by the compiler. Runtime (dynamic) polymorphism is achieved via method overriding, resolved by the JVM through dynamic dispatch at execution.

How is abstraction achieved in Java?

Through abstract classes (declared abstract, may have abstract and concrete methods) and interfaces (contracts of method signatures), which hide implementation while exposing functionality.

Compare an abstract class and an interface (pre-Java 8 distinctions).

Abstract class: can have constructors, instance fields, and both abstract & concrete methods; a class extends only one. Interface: traditionally only abstract methods and constants (public static final); a class can implement many. (Java 8+ added default/static methods to interfaces.)

What is encapsulation and how is it implemented in Java?

Encapsulation binds data and methods together while restricting direct access. It is implemented by declaring fields private and exposing them through public getter and setter methods.

What is the difference between a checked and an unchecked exception?

Checked exceptions (subclasses of Exception, not RuntimeException) must be declared or handled at compile time (e.g. IOException). Unchecked exceptions (subclasses of RuntimeException) occur at runtime and need not be declared (e.g. NullPointerException).

Describe the structure of a try-catch-finally block.

try holds code that may throw an exception; catch handles a specific exception type; finally always executes (whether or not an exception occurred), typically for cleanup like closing resources.

What is the difference between throw and throws?

throw is a statement that explicitly raises an exception instance (throw new IOException();). throws is a clause in a method signature declaring which checked exceptions the method may propagate.

What is the root class of the Java exception hierarchy, and how does Error differ from Exception?

Throwable is the root; its two subclasses are Exception (recoverable, application-level problems) and Error (serious, usually unrecoverable JVM-level problems like OutOfMemoryError).

What is the Java Collections Framework?

A unified architecture of interfaces (List, Set, Queue, Map) and implementations (ArrayList, HashSet, LinkedList, HashMap, etc.) plus algorithms for storing and manipulating groups of objects.

Differentiate List, Set, and Map in the Collections Framework.

List: ordered, allows duplicates, index-based (ArrayList, LinkedList). Set: no duplicates, typically unordered (HashSet, TreeSet). Map: key-value pairs with unique keys (HashMap, TreeMap). Note: Map does not extend Collection.

Compare ArrayList and LinkedList.

ArrayList uses a dynamic array: fast random access $O(1)$, slower mid-list insert/delete $O(n)$. LinkedList uses a doubly linked list: fast insert/delete $O(1)$ at known nodes, slower random access $O(n)$.

Compare HashMap and TreeMap.

HashMap: unordered, allows one null key, average $O(1)$ access. TreeMap: sorted by key order (Red-Black tree), no null key, $O(\log n)$ access.

What are generics and what key benefit do they provide?

Generics allow types to be parameterized (e.g. List<String>), providing compile-time type safety and eliminating explicit casts, so type errors are caught at compilation rather than runtime.

What is the difference between a process and a thread, and name the two ways to create a thread in Java.

A process is an independent program with its own memory; a thread is a lightweight unit of execution within a process sharing its memory. Create a thread by extending Thread or implementing Runnable (then passing it to a Thread). The synchronized keyword prevents concurrent access to shared resources.

What are the two main categories of Java I/O streams and what is the difference?

Byte streams (InputStream/OutputStream) handle raw 8-bit binary data (e.g. FileInputStream). Character streams (Reader/Writer) handle 16-bit Unicode text data (e.g. FileReader, BufferedReader).