Java集合类-ArrayList分析

Posted 2020-10-10

ArrayList的特点

可以动态扩容

非线程安全

支持序列化

线程安全的List Collections.synchronizedList、CopyOnWriteArrayList

成员变量

private static final int DEFAULT_CAPACITY = 10; // 初始大小

transient Object[] elementData;  // 存储元素的数组

private int size; //容器大小

基本方法

增 add

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

private void ensureCapacityInternal(int minCapacity) {
    if (elementData == DEFAULTCAPACITY_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);
}

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);
}

 

删 remove

改 set

查 get

 

ArrayList扩容原理

如果新加入元素后数组容量不够需要进行扩容，执行grow方法

默认扩容为之前的1.5倍，如果容量不够则直接扩充为加入当前元素后的大小 

然后利用Arrays.copyOf进行数组的复制

相关类和方法

Arrays.copyOf()

System.arraycopy()

public static native void arraycopy(

　　Object src,
　　int srcPos,
　　Object dest,
　　int destPos,
　　int length

);