List

Colletion

容器继承图

https://www.jianshu.com/p/31ed50ab01e3

Java List

List <– ArrayList LinkedList

ArrayList

1. ```
   ArrayList arrayList = new ArrayList<>();

    得到一个object数组 `private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};`
   
   source

   public ArrayList() {

   this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
   

   }

   2. ```
      arrayList.add(1);
      arrayList.add(2);

   source

   public boolean add(E e) {
       ensureCapacityInternal(size + 1);  // Increments modCount!!
       elementData[size++] = e;
       return true;
   }
   
    
    private void ensureCapacityInternal(int minCapacity) {
        ensureExplicitCapacity(calculateCapacity(elementData, minCapacity));
    }
    

   • 先看看calculateCapacity

     private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
     private static final int DEFAULT_CAPACITY = 10;
     
     private static int calculateCapacity(Object[] elementData, int minCapacity) {
         if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
             return Math.max(DEFAULT_CAPACITY, minCapacity);
         }
         return minCapacity;
     }

     if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) minCapacity==10

   • ensureExplicitCapacity()

     private void ensureExplicitCapacity(int minCapacity) {
         modCount++;
     
         // overflow-conscious code
         if (minCapacity - elementData.length > 0)
             grow(minCapacity);
     }
     
      private void grow(int minCapacity) {
             // overflow-conscious code
             int oldCapacity = elementData.length;
             int newCapacity = oldCapacity + (oldCapacity >> 1);
             if (newCapacity - minCapacity < 0)
                 newCapacity = minCapacity;
             if (newCapacity - MAX_ARRAY_SIZE > 0)
                 newCapacity = hugeCapacity(minCapacity);
             // minCapacity is usually close to size, so this is a win:
             elementData = Arrays.copyOf(elementData, newCapacity);
     }

     添加arrayList.add(1);时，size 为10的数组， elementData[size++] = e; 注意size初始化值==0，程序先 执行elementData[0]=1,然后是size++;

     当添加的数是11时， int newCapacity = oldCapacity + (oldCapacity >> 1);开始执行 10 + 1010>>1 = 10+5,申请了5个空间

     然后get()可以获取element

   • 源码简写

     int size =0;
     Object[] elementData= {};
     Object[] elementArr = Arrays.copyOf(elementData, 10);
     elementArr[size++] = 5;
     elementArr[size++] = 7;
     for ( Object el :elementArr){
         System.out.print(el+"  ");
     }
     System.out.println(elementArr[0]);

LinkedList

源码功能如图所示

void linkLast(E e) {
    final Node<E> l = last;
    final Node<E> newNode = new Node<>(l, e, null);
    last = newNode;
    if (l == null)
        first = newNode;
    else
        l.next = newNode;
    size++;
    modCount++;
}

private static class Node<E> {
        E item;
        Node<E> next;
        Node<E> prev;

        Node(Node<E> prev, E element, Node<E> next) {
            this.item = element;
            this.next = next;
            this.prev = prev;
        }
    }

List iterator

List crunchifyList = new ArrayList();

​ // add 4 different values to list

​ crunchifyList.add(“Facebook”);

​ crunchifyList.add(“Paypal”);

​ crunchifyList.add(“Google”);

​ crunchifyList.add(“Yahoo”);

​ // Other way to define list is - we will not use this list :)

​ List crunchifyListNew = Arrays.asList(“Facebook”, “Paypal”, “Google”, “Yahoo”);

• ​ Iterator - Returns an iterator over the elements in this list in proper sequence.

  Iterator<String> crunchifyIterator = crunchifyList.iterator();
    
   while(crunchifyIterator.hasNext()) {
    
     System.out.println(crunchifyIterator.next());
    
   }

• // ListIterator - traverse a list of elements in either forward or backward order

​ // An iterator for lists that allows the programmer to traverse the list in either direction, modify the list during iteration,

​ // and obtain the iterator’s current position in the list.

ListIterator<String> crunchifyListIterator = crunchifyList.listIterator();
      while (crunchifyListIterator.hasNext()) {
          System.out.println(crunchifyListIterator.next());
      }

• Iterable.forEach() util: Returns a sequential Stream with this collection as its source

  crunchifyList.forEach((temp) -> {
    
    System.out.println(temp);
    
  });

• collection Stream.forEach() util: Returns a sequential Stream with this collection as its source

crunchifyList.stream().forEach((crunchifyTemp) -> System.out.println(crunchifyTemp));

kotlin List

var mPatientList = patientList.filter { it.patientCode == patientCode }

return mQnList?.let { it ->
    it.filter { it.type == type }.map { it.value }
}

sequence

https://zhuanlan.zhihu.com/p/38258597

https://juejin.cn/post/7022429745874731045

https://winterbe.com/posts/2018/07/23/kotlin-sequence-tutorial/

https://zhuanlan.zhihu.com/p/38258597