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Put
//SparseArray.java
public void put(int key, E value) {
//二分查找,SparseArray是由小到大排序的
//找到是返回该key对应的index
//没找到时该key在这时应该放置index的补运算的结果(负数)
int i = ContainerHelpers.binarySearch(mKeys, mSize, key);
if (i >= 0) { //找到
mValues[i] = value;
} else { //没找到
i = ~i; //求补,得到该放置的位置.
if (i < mSize && mValues[i] == DELETED) { //该放置的位置没有数据在还没有元素/1个元素或者有进行删除数据的时候出现
mKeys[i] = key;
mValues[i] = value;
return;
}
if (mGarbage && mSize >= mKeys.length) {
gc(); //数据紧凑
// Search again because indices may have changed.
i = ~ContainerHelpers.binarySearch(mKeys, mSize, key);
}
mKeys = GrowingArrayUtils.insert(mKeys, mSize, i, key);
mValues = GrowingArrayUtils.insert(mValues, mSize, i, value);
mSize++;
}
}
//SparseArray.java
//使数据紧凑(数据集中在数组前端)
private void gc() {
// Log.e("SparseArray", "gc start with " + mSize);
int n = mSize;
int o = 0;
int[] keys = mKeys;
Object[] values = mValues;
for (int i = 0; i < n; i++) {
Object val = values[i];
if (val != DELETED) {
if (i != o) {
keys[o] = keys[i];
values[o] = val;
values[i] = null;
}
o++;
}
}
mGarbage = false;
mSize = o;
// Log.e("SparseArray", "gc end with " + mSize);
}
//ContainerHelpers.java
// This is Arrays.binarySearch(), but doesn't do any argument validation.
//[不做参数范围检测]
static int binarySearch(int[] array, int size, int value) {
int lo = 0;
int hi = size - 1;
while (lo <= hi) {
final int mid = (lo + hi) >>> 1;
final int midVal = array[mid];
if (midVal < value) {
lo = mid + 1;
} else if (midVal > value) {
hi = mid - 1;
} else {
return mid; // value found
}
}
return ~lo; // value not present
}
//GrowingArrayUtils.java
public static T[] insert(T[] array, int currentSize, int index, T element) {
assert currentSize <= array.length;
if (currentSize + 1 <= array.length) {
//(T[] src, int srcPos, T[] dst, int dstPos, int length)
//也就是把array的index(包括自身)后的元素往后移动1个单位
System.arraycopy(array, index, array, index + 1, currentSize - index);
array[index] = element;
return array;
}
//数组容量不够,扩容
@SuppressWarnings("unchecked")
T[] newArray = ArrayUtils.newUnpaddedArray((Class)array.getClass().getComponentType(),
growSize(currentSize));
//growSize(currentSize) ==> return currentSize <= 4 ? 8 : currentSize * 2;
System.arraycopy(array, 0, newArray, 0, index);
newArray[index] = element;
System.arraycopy(array, index, newArray, index + 1, array.length - index);
return newArray;
}
Delete & Remove
//SparseArray.java
public void remove(int key) {
delete(key);
}
public void delete(int key) {
int i = ContainerHelpers.binarySearch(mKeys, mSize, key);
if (i >= 0) {
if (mValues[i] != DELETED) {
mValues[i] = DELETED;
mGarbage = true;
//在这里并没有把mSize减一和做数组紧缩操作,而是在要用的做,
//比如调getSize()就会做数组紧缩,这样才可以得到真正的size
}
}
}
Append
//SparseArray.java
//由于SparseArray几乎所有的操作都是基于二分查找算法,所以append的实现肯定不能
//直接append
public void append(int key, E value) {
//如果值不够大,当然排不到最后,转为put
if (mSize != 0 && key <= mKeys[mSize - 1]) {
put(key, value);
return;
}
if (mGarbage && mSize >= mKeys.length) {
gc();
}
mKeys = GrowingArrayUtils.append(mKeys, mSize, key);
mValues = GrowingArrayUtils.append(mValues, mSize, value);
mSize++;
}
//GrowingArrayUtils.java
public static T[] append(T[] array, int currentSize, T element) {
assert currentSize <= array.length;
//申请新容量
if (currentSize + 1 > array.length) {
@SuppressWarnings("unchecked")
T[] newArray = ArrayUtils.newUnpaddedArray(
(Class) array.getClass().getComponentType(), growSize(currentSize));
System.arraycopy(array, 0, newArray, 0, currentSize);
array = newArray;
}
array[currentSize] = element;
return array;
}