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  • ArrayList实现动态数组原理

    addAll方法和申请数组大小函数

     public boolean addAll(Collection<? extends E> c) {  
       Object[] a = c.toArray();  
        int numNew = a.length;  
        ensureCapacity(size + numNew);      // Increments modCount  
        System.arraycopy(a, 0, elementData, size, numNew);  
        size += numNew;  
        return numNew != 0;  
     }
    
    public void ensureCapacity(int minCapacity) {  
        modCount++;  
        int oldCapacity = elementData.length;  
        if (minCapacity > oldCapacity) {     //判断是否大于默认申请空间
            Object oldData[] = elementData;    
            int newCapacity = (oldCapacity * 3)/2 + 1;  //增加50%+1
                if (newCapacity < minCapacity)          //如果还是不够,直接让其等于最新的长度
                    newCapacity = minCapacity;  
          // minCapacity is usually close to size, so this is a win:  
          elementData = Arrays.copyOf(elementData, newCapacity);       //新的数组
        }  
     }

    照例来看一下addAll方法,ensureCapacityInternal判断当前的数字是否大于了申请的长度,如果空间不够了,在申请 1.5倍的空间+1,如果还是不够,直接让最新的长度等于需要的长度,然后将旧的数组给新的数组。

    参考:http://blog.csdn.net/ZXC641483573/article/details/78106552?locationNum=7&fps=1

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  • 原文地址:https://www.cnblogs.com/meituan/p/7941126.html
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