Array List的remove(Object o)源码

比眉伴天荒 2024-04-18 13:29 54阅读 0赞

/**
 * Removes the first occurrence of the specified element from this list,
 * if it is present. 
 * 移除集合中出现的第一个和指定元素匹配(存在的话)的元素(并返回true)。
 * If the list does not contain the element, it is
 * unchanged. 
 * 不存在的话，不做修改(并返回false)。
 * More formally, removes the element with the lowest index
 * <tt>i</tt> such that
 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>
 * (if such an element exists). Returns <tt>true</tt> if this list
 * contained the specified element (or equivalently, if this list
 * changed as a result of the call).
 *
 * @param o element to be removed from this list, if present
 * @return <tt>true</tt> if this list contained the specified element
 */
 public boolean remove(Object o) {
 if (o == null) {
 // o == null时，从0遍历elementData是否有元素为null，有则删除
 for (int index = 0; index < size; index++)
 if (elementData[index] == null) {
 fastRemove(index);
 return true;
 }
 } else {
 // o != null时,从0开始遍历集合删除遇到的第一个equals(o)的元素(并不是删除集合中所有和equals(o)的元素)，并返回true
 for (int index = 0; index < size; index++)
 if (o.equals(elementData[index])) {
 fastRemove(index);
 return true;
 }
 }
 return false;
 }
 
 /*
 * Private remove method that skips bounds checking and does not
 * return the value removed.
 */
 private void fastRemove(int index) {
 modCount++;
 int numMoved = size - index - 1;
 if (numMoved > 0)
 // 调用System中的native方法arraycopy
 // 参数说明(从左至右):源数组 源数组中开始位置 目标数组 目标数组中开始位置 移动个数
 System.arraycopy(elementData, index+1, elementData, index,
 numMoved);
 // 上一步操作之后 elementData尾部数据还在 手动置null，并把elementData的长度size值减一(很重要) 交给GC
 elementData[--size] = null; // clear to let GC do its work
 }
 
 
 /**
 * java.lang.System
 *
 * Copies an array from the specified source array, beginning at the
 * specified position, to the specified position of the destination array.
 * 从 指定源数组 中的 指定位置 开始 ，复制一个新数组到 目标数组 的 指定位置。
 *
 * A subsequence of array components are copied from the source
 * array referenced by <code>src</code> to the destination array
 * referenced by <code>dest</code>. The number of components copied is
 * equal to the <code>length</code> argument. The components at
 * positions <code>srcPos</code> through
 * <code>srcPos+length-1</code> in the source array are copied into
 * positions <code>destPos</code> through
 * <code>destPos+length-1</code>, respectively, of the destination
 * array.
 * 参数说明
 *
 * 
 * If the <code>src</code> and <code>dest</code> arguments refer to the
 * same array object, then the copying is performed as if the
 * components at positions <code>srcPos</code> through
 * <code>srcPos+length-1</code> were first copied to a temporary
 * array with <code>length</code> components and then the contents of
 * the temporary array were copied into positions
 * <code>destPos</code> through <code>destPos+length-1</code> of the
 * destination array.
 * 如果源数组和目标数组指向了同一个数组，复制操作首先会把源数组中(srcPos 到 
 * srcPos+length-1)位置的元素复制到一个临时数组，然后把这个临时数组复制到目标
 * 数组的(destPos 到 destPos+length-1)位置。
 *
 * 
 * If <code>dest</code> is <code>null</code>, then a
 * <code>NullPointerException</code> is thrown.
 * 目标数组为null时，抛NullPointerException。
 *
 * 
 * If <code>src</code> is <code>null</code>, then a
 * <code>NullPointerException</code> is thrown and the destination
 * array is not modified.
 * 源数组为null时，抛NullPointerException，且不对目标数组做任何修改。
 *
 * 
 * Otherwise, if any of the following is true, an
 * <code>ArrayStoreException</code> is thrown and the destination is
 * not modified:
 * 有以下任一情况：抛NullPointerException，且不对目标数组做任何修改(src
 * 或dest指向非数组及两数组元素类型不同等)。
 * <ul>
 * <li>The <code>src</code> argument refers to an object that is not an
 * array.
 * <li>The <code>dest</code> argument refers to an object that is not an
 * array.
 * <li>The <code>src</code> argument and <code>dest</code> argument refer
 * to arrays whose component types are different primitive types.
 * <li>The <code>src</code> argument refers to an array with a primitive
 * component type and the <code>dest</code> argument refers to an array
 * with a reference component type.
 * <li>The <code>src</code> argument refers to an array with a reference
 * component type and the <code>dest</code> argument refers to an array
 * with a primitive component type.
 * </ul>
 *
 * 
 * Otherwise, if any of the following is true, an
 * <code>IndexOutOfBoundsException</code> is
 * thrown and the destination is not modified:
 * 有以下任一情况：抛IndexOutOfBoundsException，且不对目标数组做任何修改(数组元素个数)。
 * <ul>
 * <li>The <code>srcPos</code> argument is negative.
 * <li>The <code>destPos</code> argument is negative.
 * <li>The <code>length</code> argument is negative.
 * <li><code>srcPos+length</code> is greater than
 * <code>src.length</code>, the length of the source array.
 * <li><code>destPos+length</code> is greater than
 * <code>dest.length</code>, the length of the destination array.
 * </ul>
 * 
 * Otherwise, if any actual component of the source array from
 * position <code>srcPos</code> through
 * <code>srcPos+length-1</code> cannot be converted to the component
 * type of the destination array by assignment conversion, an
 * <code>ArrayStoreException</code> is thrown. In this case, let
 * k be the smallest nonnegative integer less than
 * length such that <code>src[srcPos+</code>k<code>]</code>
 * cannot be converted to the component type of the destination
 * array; when the exception is thrown, source array components from
 * positions <code>srcPos</code> through
 * <code>srcPos+</code>k<code>-1</code>
 * will already have been copied to destination array positions
 * <code>destPos</code> through
 * <code>destPos+</code>k<code>-1</code> and no other
 * positions of the destination array will have been modified.
 * (Because of the restrictions already itemized, this
 * paragraph effectively applies only to the situation where both
 * arrays have component types that are reference types.)
 *
 * @param src the source array.
 * @param srcPos starting position in the source array.
 * @param dest the destination array.
 * @param destPos starting position in the destination data.
 * @param length the number of array elements to be copied.
 * @exception IndexOutOfBoundsException if copying would cause
 * access of data outside array bounds.
 * @exception ArrayStoreException if an element in the <code>src</code>
 * array could not be stored into the <code>dest</code> array
 * because of a type mismatch.
 * @exception NullPointerException if either <code>src</code> or
 * <code>dest</code> is <code>null</code>.
 */
 public static native void arraycopy(Object src, int srcPos,
 Object dest, int destPos,
 int length);