• ArrayList代码学习


    ArrayList (数组链表)使用Object数组作为存储。

        /**
         * The array buffer into which the elements of the ArrayList are stored.
         * The capacity of the ArrayList is the length of this array buffer. Any
         * empty ArrayList with elementData == EMPTY_ELEMENTDATA will be expanded to
         * DEFAULT_CAPACITY when the first element is added.
         */
        private transient Object[] elementData;
    
        /**
         * Shared empty array instance used for empty instances.
         */
        private static final Object[] EMPTY_ELEMENTDATA = {};
    

      

     默认构造函数为:

        /**
         * Constructs an empty list with an initial capacity of ten.
         */
        public ArrayList() {
            super();
            this.elementData = EMPTY_ELEMENTDATA;
        }
    

     构造一个空的链表,该链表没有进行初始化,在调用其add()方法时,进行了初始化:

        /**
         * Appends the specified element to the end of this list.
         *
         * @param e element to be appended to this list
         * @return <tt>true</tt> (as specified by {@link Collection#add})
         */
        public boolean add(E e) {
            ensureCapacityInternal(size + 1);  // Increments modCount!!
            elementData[size++] = e;
            return true;
        }
    

     ensureCapacityInternal()方法是

        private void ensureCapacityInternal(int minCapacity) {
            if (elementData == EMPTY_ELEMENTDATA) {
                minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
            }
    
            ensureExplicitCapacity(minCapacity);
        }
    
        private void ensureExplicitCapacity(int minCapacity) {
            modCount++;
    
            // overflow-conscious code
            if (minCapacity - elementData.length > 0)
                grow(minCapacity);
        }
    
        /**
         * Increases the capacity to ensure that it can hold at least the
         * number of elements specified by the minimum capacity argument.
         *
         * @param minCapacity the desired minimum capacity
         */
        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);
        }
    

      

    get()方法:

        /**
         * Returns the element at the specified position in this list.
         *
         * @param  index index of the element to return
         * @return the element at the specified position in this list
         * @throws IndexOutOfBoundsException {@inheritDoc}
         */
        public E get(int index) {
            rangeCheck(index);
    
            return elementData(index);
        }
    
        @SuppressWarnings("unchecked")
        E elementData(int index) {
            return (E) elementData[index];
        }
    

       

      

  • 相关阅读:
    PHP面试总结
    yii2-dingtalk 钉钉群机器人
    分布式锁机制原理及实现方式
    strtotime的一个使用问题
    JavaScript的程序构成
    libsvm源码凝视+算法描写叙述:svm_train
    android事件分发(二)
    Windows 上通过本地搭建 Jekyll环境
    重点:用户画像
    easyui英文提示变中文
  • 原文地址:https://www.cnblogs.com/lixiaolun/p/8884277.html
Copyright © 2020-2023  润新知