ArrayList源码解读之remove(Object o)和remve(int index)

亦凉 2022-02-27 12:14 245阅读 0赞

### 文章目录 ###

*  ArrayList源码解读之remove(Object o)和remve(int index)
 *   *  样例
     *  remove(Object o)
     *  fastRemove(index)私有方法
     *  System.arraycopy()方法
     *  remove(int index)
     *  System.arraycopy()方法
     *  remove(Object o)数组结构图解

# ArrayList源码解读之remove(Object o)和remve(int index) #

## 样例 ##

/**
         * 2.测试remove和fastRemove区别
         * E remove(int index)
         */
        public static void test2(){
            ArrayList list1 = new ArrayList();
            list1.add(1);
            list1.add(2);
            list1.add(5);
            list1.add(6);
            list1.add(null);
            list1.add(7);
    
            list1.remove(Integer.valueOf(6));
            list1.remove(Integer.valueOf(2));
            list1.remove(null);
            list1.remove(1);
        }

## remove(Object o) ##

public boolean remove(Object o) {
            if (o == null) {
                for (int index = 0; index < size; index++)
                    if (elementData[index] == null) {//找到第一个空元素,并删除掉
                        fastRemove(index);
                        return true;
                    }
            } else {
                for (int index = 0; index < size; index++)
                    if (o.equals(elementData[index])) {
                        fastRemove(index);
                        return true;
                    }
            }
            return false;
        }

## fastRemove(index)私有方法 ##

private void fastRemove(int index) {
            modCount++;//记录对象list被修改次数
            int numMoved = size - index - 1;
            if (numMoved > 0)
                System.arraycopy(elementData, index+1, elementData, index,numMoved);
            elementData[--size] = null; // clear to let GC do its work
        }

## System.arraycopy()方法 ##

public static native void arraycopy(Object src,  int  srcPos,Object dest, int destPos,int length);

## remove(int index) ##

public E remove(int index) {
            rangeCheck(index);//边界检测
    
            modCount++;
            E oldValue = elementData(index);//返回要删除索引位置的元素
    
            int numMoved = size - index - 1;
            if (numMoved > 0)
                System.arraycopy(elementData, index+1, elementData, index,numMoved);
            elementData[--size] = null; // clear to let GC do its work
    
            return oldValue;
        }

## System.arraycopy()方法 ##

public static native void arraycopy(Object src,  int  srcPos,Object dest, int destPos,int length);

## remove(Object o)数组结构图解 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTQzNDQ2Njg_size_16_color_FFFFFF_t_70]

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