---
id: java-algorithms
title: "Java Algorithms"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["Collections class algorithms", "자바 알고리즘"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.88
created_at: 2026-07-04
updated_at: 2026-07-04
review_reason: ""
merge_history: []
tags: ["java", "programming", "w3schools", "algorithms", "collections"]
raw_sources: ["https://www.w3schools.com/java/java_algorithms.asp"]
applied_in: []
github_commit: ""
---

# [[Java Algorithms]]

## 🎯 한 줄 통찰 (One-line insight)
`Collections.binarySearch()` REQUIRES the list to already be sorted — the example explicitly calls `Collections.sort(names)` immediately before `binarySearch()`, since binary search's speed advantage depends entirely on the data being in order; searching an unsorted list with it gives undefined/incorrect results. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Algorithm** — a procedure to solve a problem (search, sort, manipulate data structures). [S1]
- **`Collections` class** — provides built-in algorithms in `java.util`, avoiding the need to hand-write them. [S1]
- **`Collections.binarySearch(list, key)`** — fast search, but requires a pre-sorted list. [S1]
- **`Collections.sort(list)`** / **`sort(list, reverseOrder())`** — ascending/descending sort. [S1]
- **`Collections.max()` / `min()`** — largest/smallest element. [S1]
- **`Collections.shuffle()`** — randomly reorders elements. [S1]
- **`Collections.frequency(list, element)`** — counts occurrences of a value. [S1]
- **`Collections.swap(list, i, j)`** — swaps two elements by index. [S1]

## 📖 세부 내용 (Details)
- Binary search (must sort first): `Collections.sort(names); int index = Collections.binarySearch(names, "Angie");`. [S1]
- Max/min: `Collections.max(numbers); Collections.min(numbers);`. [S1]
- Shuffle: `Collections.shuffle(cards);`. [S1]
- Frequency: `int count = Collections.frequency(fruits, "Banana");`. [S1]
- Swap: `Collections.swap(fruits, 0, 2); // Swap first and third element`. [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
- **정렬 선행 조건**: binarySearch()는 리스트가 반드시 정렬되어 있어야 정확히 동작한다는 점이 예제에서 명시적으로 지켜짐. [S1]

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — 카드 셔플(Collections.shuffle)이나 과일 빈도 계산(frequency)이 실전 알고리즘 활용의 대표 사례다. [S1]

## 💻 코드 패턴 (Code patterns)
Sort-then-binarySearch pattern (Java):
```java
ArrayList<String> names = new ArrayList<>();
names.add("Liam"); names.add("Jenny"); names.add("Kasper"); names.add("Angie");
Collections.sort(names); // required before binarySearch
int index = Collections.binarySearch(names, "Angie");
```

## ✅ 검증 상태 및 신뢰도
- **상태:** draft
- **검증 단계:** conceptual
- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
- **신뢰 점수:** 0.88
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[Java Tutorial]]
- **관련 개념:** [[Java Sort List]], [[Java Iterator]], [[Java Advanced Sorting]]
- **참조 맥락:** Collections 클래스의 내장 알고리즘 — 고급 정렬(Advanced Sorting) 챕터로 이어짐.

## 📚 출처 (Sources)
- [S1] W3Schools — Java Algorithms — https://www.w3schools.com/java/java_algorithms.asp

## 📝 변경 이력 (Change history)
- 2026-07-04: Initial draft synthesized from the W3Schools "Java Algorithms" page (Astra wiki-curation, P-Reinforce v3.1 format).