ArrayList源码分析

ArrayList源码分析

1. private static final int DEFAULT_CAPACITY = 10;
   

添加任意一个元素之后默认容量 DEFAULT_CAPACITY = 10 如果没有添加元素 默认容量是0

当添加元素超过容量时，会进行扩容，扩容为原来的1.5倍。

2. transient Object[] elementData; // non-private to simplify nested class access
   

存放元素数组 elementData

3. private int size;
   

实际元素个数 size 默认值为0

4. private static final Object[] EMPTY_ELEMENTDATA = {};
   

5. private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
   

6. add()方法 添加元素

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) {
            //DEFAULT_CAPACITY:10   minCapacity:1    
            minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity); //10
        }

        ensureExplicitCapacity(minCapacity); //10
    }


private void ensureExplicitCapacity(int minCapacity) {  //10
        modCount++; 

        // overflow-conscious code
        if (minCapacity - elementData.length > 0)  //10-0 > 0
            grow(minCapacity);
    }

private void grow(int minCapacity) {  //10
        // overflow-conscious code
        int oldCapacity = elementData.length; //0
        int newCapacity = oldCapacity + (oldCapacity >> 1);//0
        if (newCapacity - minCapacity < 0)  //0-10
            newCapacity = minCapacity; //10
        if (newCapacity - MAX_ARRAY_SIZE > 0)  //MAX_ARRAY_SIZE = 0x7fffffff
            newCapacity = hugeCapacity(minCapacity);
        // minCapacity is usually close to size, so this is a win:
        elementData = Arrays.copyOf(elementData, newCapacity);  //10
    }