数组操作 和 list到数组
常在看代码的时候，看到这样的数组的操作：
Integer[] arr1 = new Integer[0];for (int i=0; i < 100000; i++) {Integer[] arr2 = new Integer[arr1.length + 1];System.arraycopy(arr1, 0, arr2, 0, arr1.length);arr2[arr1.length] = i;arr1 = arr2;}??实现的就是，向数组中加元素，这个数组是不定常的，所以里面会新new一个数组，然后又copy，又赋值的。感觉就是头大，效率不高，代码写的太朴实无华了。
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比较List的实现：
public class Tst {public static void main(String[] args) {long startTime = System.currentTimeMillis();List<Integer> list = new ArrayList<Integer>();for (int i=0; i < 10000000; i++)list.add(i);list.toArray(new Integer[list.size()]);System.out.println("Runned time : " + (System.currentTimeMillis()-startTime));startTime = System.currentTimeMillis();Integer[] arr1 = new Integer[0];for (int i=0; i < 100000; i++) {Integer[] arr2 = new Integer[arr1.length + 1];System.arraycopy(arr1, 0, arr2, 0, arr1.length);arr2[arr1.length] = i;arr1 = arr2;}System.out.println("Runned time : " + (System.currentTimeMillis()-startTime));}}?
结果：
/** * Increases the capacity of this <tt>ArrayList</tt> instance, if * necessary, to ensure that it can hold at least the number of elements * specified by the minimum capacity argument. * * @param minCapacity the desired minimum capacity */public void ensureCapacity(int minCapacity) {modCount++;int oldCapacity = elementData.length;if (minCapacity > oldCapacity) { Object oldData[] = elementData; int newCapacity = (oldCapacity * 3)/2 + 1; if (newCapacity < minCapacity)newCapacity = minCapacity; // minCapacity is usually close to size, so this is a win: elementData = Arrays.copyOf(elementData, newCapacity);}}??
也就 newCapacity = (oldCapacity * 3)/2 + 1;
并不是数组那种总是加1的方式。?