Java Exam Questions

Most-asked Java theory + programs in B.Tech, MCA, and IT diploma exams.

Overview

Frequently-asked Java exam questions across theory, programs, OOP, and JDBC. Use to revise the night before.

1. Theory Questions

What is Java? Who developed it? Object-oriented, platform-independent language; James Gosling, Sun Microsystems, 1995.
JDK vs JRE vs JVM?
- JVM — runs .class files
- JRE — JVM + standard libraries (to RUN)
- JDK — JRE + compiler javac (to BUILD)
Why is Java platform independent? javac compiles to bytecode which any JVM can run — "Write Once, Run Anywhere."
What are the features of Java? OOP, robust, secure, multi-threaded, distributed, portable.
Difference: == vs .equals()? == compares references; .equals() compares values.

2. Common Programs

WAP to check Armstrong / palindrome / prime.
WAP to reverse a string without library.
WAP to demonstrate single-level / multi-level / hierarchical inheritance.
WAP for try-catch-finally with ArithmeticException.
WAP using threads — extend Thread and implement Runnable.

3. OOP Section (very high yield)

4 pillars: Encapsulation, Inheritance, Polymorphism, Abstraction.
Method overloading — same name, different params (compile-time).
Method overriding — subclass redefines parent method (run-time).
Abstract class vs interface? Abstract can have non-abstract methods; interface (pre-Java 8) only abstract; both can't be instantiated.
super vs this? super → parent class members; this → current object.

4. Output / Predict-the-output

java
System.out.println(10 + 20 + "Java");    // 30Java
System.out.println("Java" + 10 + 20);    // Java1020
int x = 5; System.out.println(x++ + ++x); // 12

5. JDBC / Collections (often asked)

JDBC steps: Load driver → connect → statement → execute → process → close.
ArrayList vs LinkedList? ArrayList: random access O(1), insert O(n). LinkedList: insert O(1), access O(n).
HashMap vs HashTable? HashMap is unsynchronized + allows null; HashTable is synchronized + no null.

6. Pro Tips

Always close DB connections in finally (or use try-with-resources).
String is immutable — manipulations create new objects.
final on var → constant; on method → can't override; on class → can't extend.
Mention garbage collection is automatic via System.gc() hint.

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# program

Program

Java

// Quick OOP demo
class A { void show() { System.out.println("A"); } }
class B extends A { void show() { System.out.println("B"); } }
public class Main {
    public static void main(String[] a) {
        A x = new B();
        x.show();   // B  (run-time polymorphism)
    }
}

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