1.返回刪除元素的刪除方法

public E remove(int index) {rangeCheck(index);modCount++;//記錄修改次數的變量E oldValue = elementData(index);//根據數組下標拿到指定元素int numMoved = size - index - 1;//計算移動位數if (numMoved > 0)System.arraycopy(elementData, index+1, elementData, index,numMoved);//把elementData中(index+1,size-1)復制到(index,size-1)elementData[--size] = null; // size-1，最后一個元素置為nullreturn oldValue;
}

下標檢查，如果大于數組的size，拋出異常

private void rangeCheck(int index) {if (index >= size)throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}

2.返回一個boolean值的刪除方法

2.1傳進來null，刪除第一個值為null的值(注意此時加入了兩個null值)

此時執行了一句list.remove(null);只刪除了在物理位置上比較靠前的null,第二次刪除才會刪除第二個null

public boolean remove(Object o) {if (o == null) {for (int index = 0; index < size; index++)if (elementData[index] == null) {fastRemove(index);return true;}} else {for (int index = 0; index < size; index++)if (o.equals(elementData[index])) {fastRemove(index);return true;}}return false;
}

此方法執行的就是上面"返回刪除元素"方法中的內容

private void fastRemove(int index) {modCount++;int numMoved = size - index - 1;if (numMoved > 0)System.arraycopy(elementData, index+1, elementData, index,numMoved);elementData[--size] = null;
}

3.從這個列表中刪除所有未包含在指定集合中的元素

public boolean retainAll(Collection<?> c) {Objects.requireNonNull(c); // 檢查,如果此對象為空,拋出空指針異常return batchRemove(c, true);
}

private boolean batchRemove(Collection<?> c, boolean complement) {final Object[] elementData = this.elementData;int r = 0, w = 0;boolean modified = false;try {for (; r < size; r++)//如果傳入的集合c,包含當前所遍歷的數組的元素,重新整理一下list中的元素if (c.contains(elementData[r]) == complement)elementData[w++] = elementData[r];} finally {// 拋出異常后的處理(下面為JDK中的描述)// Preserve behavioral compatibility with AbstractCollection,// even if c.contains() throws.if (r != size) {System.arraycopy(elementData, r,elementData, w,size - r);w += size - r;}if (w != size) {// clear to let GC do its workfor (int i = w; i < size; i++)elementData[i] = null;modCount += size - w;size = w;modified = true;}}return modified;
}