I built a Claude Code skill that scores your legacy Java code 1–100 and modernizes it to Java 21

java dev.to

Java Claude Skills — Java 8 → Java 21 Modernization for Claude Code

AI-powered Java code modernization skill for Claude Code.
Analyzes legacy Java, generates a prioritized upgrade report, scores it 1–100, and applies every change — all inside your editor.


Why this skill?

Migrating Java 8 code to Java 21 is high-value but tedious — every codebase has the same problems:

Problem Impact
double for monetary values Silent precision loss on every FX calculation
Unguarded chained .get() calls NPE crashes in production settlement flows
synchronized HashMap Race conditions on position updates under load
Fixed thread pools Bottleneck at 200–500 concurrent trades
Boilerplate DTOs with 60+ lines Noise that obscures domain logic

This skill acts as a Senior Java Architect in your Claude Code session. It knows every Java feature from 8 through 21, enforces financial-domain safety rules, and produces code you can ship — not just advice.


Skills

Source: dev.to

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