What is the difference between String, StringBuilder, and StringBuffer?

String is immutable, StringBuilder is mutable and not synchronized, and StringBuffer is mutable and synchronized. In an interview, support it with one tradeoff and one production example.

What is the difference between checked and unchecked exceptions?

Checked exceptions must be declared or handled, while unchecked exceptions extend RuntimeException and are not enforced by the compiler. In an interview, support it with one tradeoff and one production example.

What is the difference between checked and unchecked exceptions?

Checked exceptions must be handled or declared, while unchecked exceptions are runtime exceptions that do not require explicit handling. In an interview, support it with one tradeoff and one production example.

Java10 min readUpdated Jul 17, 2026Technical Concept

Top 10 Java Coding Question

Top 10 Java Coding Question uses verified RivoHire qbank answers. Start with the strongest short answer, then review tradeoffs, scenarios, mistakes, and interview wording.

JavaJavaTop 10 Java Coding QuestionJava Interview Questions

Quick definition

Top 10 Java Coding Question uses verified RivoHire qbank answers. Start with the strongest short answer, then review tradeoffs, scenarios, mistakes, and interview wording.

Quick Summary

Topic	Questions	Source	Company Claims
Java	10	MongoDB qbank	Only shown when present in qbank

Scenario Questions

A Java change causes slower responses after traffic increases. I would isolate the hot path, apply the smallest reversible fix, and verify the result with latency, error rate, and rollback readiness.
A Java change causes slower responses after traffic increases. I would isolate the hot path, apply the smallest reversible fix, and verify the result with latency, error rate, and rollback readiness.
A Java change causes slower responses after traffic increases. I would isolate the hot path, apply the smallest reversible fix, and verify the result with latency, error rate, and rollback readiness.
Use StringBuilder for most local string-building work and StringBuffer only when synchronized mutation is required.

Common Mistakes

Wrong approach: collections is good because it is faster. Why it fails: Speed without workload, correctness, and operational context is not an engineering answer. Better answer: I would compare the workload, failure mode, and maintenance cost before using collections, then verify the result with production metrics.
Wrong approach: concurrency is good because it is faster. Why it fails: Speed without workload, correctness, and operational context is not an engineering answer. Better answer: I would compare the workload, failure mode, and maintenance cost before using concurrency, then verify the result with production metrics.
Wrong approach: jvm is good because it is faster. Why it fails: Speed without workload, correctness, and operational context is not an engineering answer. Better answer: I would compare the workload, failure mode, and maintenance cost before using jvm, then verify the result with production metrics.
Wrong approach: exceptions is good because it is faster. Why it fails: Speed without workload, correctness, and operational context is not an engineering answer. Better answer: I would compare the workload, failure mode, and maintenance cost before using exceptions, then verify the result with production metrics.
Wrong approach: HashMap always gives O(1). Why it fails: Poor hash distribution and resizing affect performance. Better answer: Average lookup is O(1), but collisions and resizing can make operations slower.

FAQ

Practice

Practice these questions in a RivoHire mock interview.

Quiz

What runs first after the synchronous call stack becomes empty?

A. Macrotask queue

B. Microtask queue

C. setTimeout queue always

D. Browser rendering always

Correct answer: microtasks run after the stack clears and before the next macrotask.

Compact Interview Questions

How does HashMap work internally in Java?

HashMap stores entries in buckets by hash code, resolves collisions, resizes by load factor, and may treeify dense buckets.

How does the Java memory model affect concurrency?

The Java memory model defines visibility, ordering, happens-before relationships, and safe publication between threads.

What is the difference between JDK, JRE, and JVM?

JDK is used to develop Java applications, JRE runs Java applications, and JVM executes Java bytecode.

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