Question 1

Can you explain the concept of polymorphism and inheritance in Java with examples?

Accepted Answer

**Inheritance:** Class extends another; inherits fields/methods. `class Dog extends Animal`. **Polymorphism:** Supertype reference → subtype; runtime dispatch. `Animal a = new Dog(); a.eat()` calls Dog's override. **Why:** Extensibility; Liskov Substitution. **Trade-off:** Composition often > inheritance. **Production:** Interfaces for contracts....

Question 2

Discuss the tech stacks and responsibilities at Morgan Stanley

Accepted Answer

**Stack:** SQL, Python/Scala, Spark, Kafka, AWS/Azure, data modeling. **Responsibilities:** Pipelines, DQ, regulatory reporting, analytics. **Domain:** Finance, risk, trading. **Why:** Compliance-heavy; low latency. **Team:** Agile; BA/QA....

Question 3

Trapping Rain Water - calculate amount of water trapped between array elements

Accepted Answer

**Why This Problem:** Teaches two-pointer and prefix reasoning. Water at i = min(max_left, max_right) - height[i].

**Approaches:** (1) Precompute max_left, max_right arrays—O(n) time, O(n) space. (2) Two pointers—O(n) time, O(1) space: move from smaller side, track max on that side. Water = max_side - height.

**Data Eng Analogy:** 'Valleys' in time-series—local minima between peaks....

Question 4

What are the key differences between interfaces and abstract classes in Java?

Accepted Answer

**Why Both Exist:** Interface = contract only (pre-Java 8). Abstract class = partial implementation + state. Interface = multiple inheritance of type; abstract = single inheritance + shared code.

**Choices:** Use interface for: capability (Serializable, Comparable), polymorphism. Use abstract class for: template method, shared state (protected fields), base pipeline stages with common setup.

**Production:** Prefer interfaces + composition....

Question 5

Write Java code to read a file using FileInputStream

Accepted Answer

**Why FileInputStream:** Raw bytes. Wrap in InputStreamReader for charset decoding, BufferedReader for line-by-line. Try-with-resources ensures close.

**For Text:** BufferedReader(readLine) is efficient—buffered. Specify charset: StandardCharsets.UTF_8....

Question 6

Write a Java program using FileInputStream and BufferedReader to read data from a local file and print the output to the console

Accepted Answer

**Pattern:** FileInputStream → InputStream (bytes). InputStreamReader(fis, charset) → chars. BufferedReader → line-by-line. Try-with-resources for auto-close.

try (var br = new BufferedReader(
        new InputStreamReader(new FileInputStream("data.txt"), StandardCharsets.UTF_8))) {
    String line;
    while ((line = br.readLine()) != null)
        System.out.println(line);
} catch (IOException e) { e.printStackTrace(); }

Question 7

Zigzag Order Traversal of a Binary Tree

Accepted Answer

**BFS with level.** Every other level, reverse before appending. Or use deque: popleft vs pop for direction. O(n).

def zigzag(root):
    if not root: return []
    res, q, ltr = [], [root], True
    while q:
        level = []
        for _ in range(len(q)):
            n = q.pop(0)
            level.append(n.val)
            if n.left: q.append(n.left)
            if n.right: q.append(n.right)
        res += level if ltr else level[::-1]
        ltr = not ltr
    return res

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