• JAVA集合结构图

JAVA集合结构图

如图所示，Collection是List，Queue，Set的父类。从左往右分析

• List(列表):

List是有序的列表，主要比较常用的为ArrayList(底层用数组实现)，LinkedList(底层用链表实现)。

1. ArrayList

• 构造方法

 //创建一个数组，无参数构造方法
public ArrayList() { 
        this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}
//定义一个数组
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
//数组创建的初始长度
private static final int DEFAULT_CAPACITY = 10;

//构造方法(有参数)
public ArrayList(int initialCapacity) {
        if (initialCapacity > 0) { //根据用户传入的值来构造数组长度
            this.elementData = new Object[initialCapacity];
        } else if (initialCapacity == 0) {
            this.elementData = EMPTY_ELEMENTDATA;//创建一个空数组  
      //private static final Object[] EMPTY_ELEMENTDATA = {};
        } else {
            throw new IllegalArgumentException("Illegal Capacity: "+
                                               initialCapacity);  //如果传入的值小于0，则报错
        }
    }

• 添加

public boolean add(E e) {
        ensureCapacityInternal(size + 1);  // Increments modCount!!
        elementData[size++] = e;
        return true;
    }

调用ensureCapacityInternal方法

    private void ensureCapacityInternal(int minCapacity) {
        if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
            minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
        }

        ensureExplicitCapacity(minCapacity);
    }

调用

  private void ensureExplicitCapacity(int minCapacity) {
        modCount++; //protected transient int modCount = 0; 修改次数

        // overflow-conscious code
        if (minCapacity - elementData.length > 0)
            grow(minCapacity);
    }

调用grow方法

  private void grow(int minCapacity) {
        // overflow-conscious code
        int oldCapacity = elementData.length;
        // 扩容0.5倍，oldCapacity向右移一位，相当于oldCapacity/2，所以newCapacity = 1.5oldCapacity
        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);
    }

• 删除

  
  ArrayList删除

2. linkedList