Tell me about a time you had to choose between two technologies or frameworks: what factors did you consider?

package com.bank.interview;

public class TechEvaluation {
    enum Method { BY_HYPE, BY_HABIT, BY_CRITERIA }

    public static String evaluate(Method method) {
        return switch (method) {
            case BY_HYPE     -> "Weak: chose because it is trending";
            case BY_HABIT    -> "Weak: chose because I already know it";
            case BY_CRITERIA -> "Strong: chose based on weighted project-specific factors";
        };
    }

    public static void main(String[] args) {
        System.out.println(evaluate(Method.BY_CRITERIA));
    }
}

Strong: chose based on weighted project-specific factors

package com.bank.interview;

import java.util.List;

public class EvalFactors {
    record Factor(String name, double weight, String rationale) {}

    public static void main(String[] args) {
        List<Factor> factors = List.of(
            new Factor("Problem fit",       0.30, "Must support ACID transactions for money"),
            new Factor("Performance",       0.20, "Must handle peak transfer load"),
            new Factor("Team familiarity",  0.20, "Team can operate it at 3am during incident"),
            new Factor("Ecosystem maturity",0.15, "Security track record, community support"),
            new Factor("Operational cost",  0.15, "Monitoring, upgrading, running in production")
        );
        factors.forEach(f -> System.out.printf("%-20s weight=%.2f  %s%n", f.name(), f.weight(), f.rationale()));
    }
}

Problem fit          weight=0.30  Must support ACID transactions for money
Performance          weight=0.20  Must handle peak transfer load
Team familiarity     weight=0.20  Team can operate it at 3am during incident
Ecosystem maturity   weight=0.15  Security track record, community support
Operational cost     weight=0.15  Monitoring, upgrading, running in production

package com.bank.interview;

import java.util.Map;

public class ContextualWeighting {
    public static Map<String, Double> weightsFor(String projectType) {
        return switch (projectType) {
            case "ledger"   -> Map.of("fit", 0.40, "performance", 0.20, "maturity", 0.20, "team", 0.10, "ops", 0.10);
            case "trading"  -> Map.of("fit", 0.20, "performance", 0.40, "maturity", 0.15, "team", 0.15, "ops", 0.10);
            case "internal" -> Map.of("fit", 0.20, "performance", 0.10, "maturity", 0.10, "team", 0.40, "ops", 0.20);
            default         -> Map.of("fit", 0.20, "performance", 0.20, "maturity", 0.20, "team", 0.20, "ops", 0.20);
        };
    }

    public static void main(String[] args) {
        System.out.println("Ledger weights: " + weightsFor("ledger"));
    }
}

package com.bank.service;

import java.util.logging.Logger;

public class ProofOfConcept {
    private static final Logger log = Logger.getLogger(ProofOfConcept.class.getName());

    public static void main(String[] args) {
        // Simulated spike results
        long relationalP99 = 12;  // ms
        long documentP99 = 45;    // ms
        boolean relationalAcid = true;
        boolean documentAcid = false;

        log.info(() -> "Relational: p99=" + relationalP99 + "ms, ACID=" + relationalAcid);
        log.info(() -> "Document:   p99=" + documentP99 + "ms, ACID=" + documentAcid);
        log.info("Winner for ledger: Relational (ACID + lower latency)");
    }
}

Relational: p99=12ms, ACID=true
Document:   p99=45ms, ACID=false
Winner for ledger: Relational (ACID + lower latency)

package com.bank.interview;

public class ComparisonResult {
    public static void main(String[] args) {
        System.out.println("Relational: fit=9, perf=8, team=9, maturity=9, ops=7 -> score=8.5");
        System.out.println("Document:   fit=4, perf=6, team=3, maturity=6, ops=5 -> score=4.6");
        System.out.println("Decision: Relational for the ledger.");
    }
}

package com.bank.interview;

public class FairCredit {
    public static void main(String[] args) {
        System.out.println("Document DB genuine strength: flexible schema for nested data.");
        System.out.println("We used it elsewhere for a reporting feature where that flexibility was the right fit.");
        System.out.println("It was not right for the ledger, but it was right for reporting.");
    }
}

package com.bank.interview;

public class Reversibility {
    public static void main(String[] args) {
        boolean highUncertainty = true;
        String advice = highUncertainty
            ? "Prefer the easily reversible option; invest less in deliberation."
            : "Both options are well-understood; pick on merit.";
        System.out.println(advice);
    }
}

package com.bank.interview;

public class TechChoiceFollowUps {
    public static void main(String[] args) {
        System.out.println("Q: Same choice today? A: Yes, the ACID requirement has not changed.");
        System.out.println("Q: Team knew Document? A: Would re-weight team factor but fit still dominates.");
        System.out.println("Q: How did it hold up? A: Zero data-integrity issues in 18 months.");
    }
}