Java: Idiomatic Efficiency Reference

Java: Idiomatic Efficiency Reference

When to Use

• Use this skill when the task matches this description: Language-specific super-code guidelines for java.

Table of Contents

1. Streams & Collections
2. Optional
3. Records & Data Classes
4. Switch Expressions
5. Concurrency
6. Error Handling
7. Anti-patterns specific to Java

1. Streams & Collections {#streams}

// ❌ Imperative accumulation
List<String> result = new ArrayList<>();
for (Item item : items) {
    if (item.isActive()) result.add(item.getName().toUpperCase());
}

// ✅
List<String> result = items.stream()
    .filter(Item::isActive)
    .map(item -> item.getName().toUpperCase())
    .toList(); // Java 16+; use .collect(Collectors.toList()) before

// ❌ Manual grouping
Map<String, List<Item>> grouped = new HashMap<>();
for (Item item : items) {
    grouped.computeIfAbsent(item.getCategory(), k -> new ArrayList<>()).add(item);
}

// ✅