# Java Collections
###### 2024/06/12
---

### Collections Framework
* 處理資料結構
* 集合的大小可以自動改變
* 皆有`toString()`方法，可以直接輸出
* 下圖為架構(每個區塊皆是**interface**)

graph TD
Collection-->Set
Collection-->List
Collection-->Queue
Map-->SortedMap
Set-->SortedSet

style Collection fill:#bbf,stroke:#259,stroke-width:2px
style Map fill:#bbf,stroke:#259,stroke-width:2px

### Collection
* 可搭配**for-each**
* 基本method:star:
* `boolean add(Object o)`
* `boolean contains(Object o)`
* `boolean isEmpty()`
* `Iterator iterator()`
* `boolean remove(Object o)`
* `int size()`
* 多元素method
* `boolean addAll(Collection c)`
* `void clear()`
* `boolean containsAll(Collection c)`
* `boolean removeAll(Collection c)`
* `boolean retainAll(Collection c)`
>將包含於c內的元素留下，其他刪除
* 陣列method
* `Object[] toArray()`
* `Object[] toArray(Object[] a)`
>指定存放的陣列，放不下會重新建立
* Collections

### Set
:::info
* 元素不重複
:::
* HashSet & LinkedHashSet
* 架構

    graph TD
    HashSet-->LinkedHashSet

* HashSet\<E>
* LinkedHashSet\<E>
* TreeSet
:::info
* 自動排序
:::
* method
* `Object first()`
* `Object last()`
* `Object ceiling(Object o)`
* `Object floor(Object o)`
* `SortedSet headSet(Object toElement)`
* `SortedSet subSet(Object fromElement, Object toElement)`
* `SortedSet(Object fromElement)`

### List
:::info
* 有次序性
* 可以用索引來儲存:star:
* 元素可重複
:::
* method
* `void add(int index, Object element)`
>插入
* `boolean addAll(int index, Collection c)`
* `Object get(int index)`
* `int indexOf(Object o)`
* `int lastIndexOf(Object o)`
* `Object remove(int index)`
* `Object set(int index, Object o)`
>替換
* `List subList(int fromIndex, int toIndex)`
* ArrayList\<E>
* 空間管理method
* `void ensureCapacity(int minCapacity)`
* `void trimToSize()`
* LinkedList\<E>
* method
* 會拋出例外
* `void addFirst(Object o)`
* `void addLast(Object o`
* `Object getFirst()`
* `Object getLast()`
* `Object removeFirst()`
* `Object removeLast()`
* 會回傳布林值或null值:star:
* `boolean offerFirst(Object o)`
* `boolean offerLast(Object o)`
* `Object peekFirst()`
* `Object peekLast()`
* `Object pollFirst()`
* `Object pollLast()`
* 同時實作了Queue和List
* 方便用來實作Queue和Stack

### Map
:::info
* key-value
* 重複加入鍵會取代先前的鍵
:::
* 基本method
* `boolean isEmpty()`
* `int size()`
* `void clear()`
* `Object put(Object key, Object value)`:star:
* `void putAll(Map t)`
* `Object remove(Object key)`:star:
* 集合操作method
* `boolean containsKey(Object key)`
* `boolean containsValue(Object value)`
* `Set entrySet()`
>"key=value"格式的Set
* `Object get(Object key)`:star:
* `Set keySet()`
>回傳key Set，可搭配**for-each**
* `Collection values()`
>回傳value Collection，可搭配**for-each**
* HashSet\<E, E>

### Iterator
:::info
* 可以直接刪除 & 瀏覽Collection中的元素
* 迭代中不可以直接修改Collection，否則會拋出例外
* 等到iterator走到`hasNext=false`時，便可以再次修改Collection
:::
* method
* `boolean hasNext()`
* `Object next()`
* `void remove()`
* `Iterator i = yourCollection.iterator();`

### Collections

static boolean
addAll(Collection c, Object... elements);

static int
binarySearch(List list, Comparable key);
static int
binarySearch(List list, Object key, Comparator c);

static void
copy(List dest, List src);
// Copies all of the elements from one list into another.

static boolean
disjoint(Collection c1, Collection c2);
// Returns true if the two specified collections have no elements in common.

static void
fill(List list, Object obj);

static int
frequency(Collection c, Object o);

static Object
max(Collection coll);
static Object
max(Collection coll, Comparator comp);

static Object
min(Collection coll);
static Object
min(Collection coll, Comparator comp);

static List
nCopies(int n, Object o);

static boolean
replaceAll(List list, Object oldVal, Object newVal);

static void
reverse(List list);

static void
sort(List list, Comparator c);

static void
swap(List list, int i, int j);