Java Interview Questions -Set 8

Java Interview Questions – Set 8

A handpicked set of Java interview questions covering core Java concepts ÔÇö equality, Java 8 features, and the final keyword. These come up frequently in product and service company interviews.

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Q1: Difference Between == and equals() in Java

• == operator: Compares object REFERENCES (memory addresses).
• equals() method: Compares object VALUES ÔÇö should be overridden for meaningful comparison.

String s1 = new String("hello");
String s2 = new String("hello");

System.out.println(s1 == s2);        // false ÔÇö different objects
System.out.println(s1.equals(s2));   // true ÔÇö same content

Q2: Main Features of Java 8

• Lambda Expressions: Enable functional programming.
• Stream API: Functional-style operations on collections.
• Default Methods: Interface methods with implementations.
• Optional Class: Avoid NullPointerException.
• New Date/Time API: java.time package.

List<String> names = Arrays.asList("John", "Jane", "Jack", "Doe");

names.stream()
     .filter(name -> name.startsWith("J"))
     .forEach(System.out::println);
// Output: John, Jane, Jack

Q3: Uses of the final Keyword

• Final Variable: Value cannot change once initialized.
• Final Method: Cannot be overridden by subclasses.
• Final Class: Cannot be subclassed (e.g., String).

// Final variable
final int MAX = 100;

// Final method
public final void display() {
    System.out.println("Cannot override");
}

// Final class
public final class Utility {
    public static final int MAX_VALUE = 100;
}

Q4: Bonus ÔÇö What is the JIT Compiler?

The Just-In-Time compiler converts Java bytecode to native machine code at runtime ÔÇö boosting performance for frequently executed methods. It is part of the JVM and is what makes Java “fast enough” for most production workloads.

Q5: Bonus ÔÇö String vs StringBuilder vs StringBuffer

• String: Immutable.
• StringBuilder: Mutable, not thread-safe ÔÇö fastest.
• StringBuffer: Mutable, thread-safe ÔÇö slower.

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Conclusion

Master these core Java questions and you will crack 70% of interview rounds. Practice writing the code, not just reading ÔÇö interviewers test fluency. For more interview prep, stay tuned to .

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