JAVA自己实现ArrayList

Posted 2022-07-29

package 集合.list.ArrayList; import java.util.Arrays; import java.util.Date; public class MyArryList //定义一个空的数组 private final static Object[] myArray = ; //定义一个默认长度10 private final static int default_length = 10; Object[] elementData; //myArryList长度 private int size = 0; //无参数构造方法,默认容量10 public MyArryList() this.elementData = myArray; //带参数构造函数 public MyArryList(int length) if (length < 0) throw new IllegalArgumentException("参数不能小于0"); this.elementData = new Object[length]; size = length; //获取长度 public int getSize() return this.size; //添加元素 public void add(Object args) //每次添加元素时需要考虑长度问题 //判断是否需要扩容 if (size >= elementData.length) this.grown(); elementData[size++] = args; //扩容方法 private void grown() if (elementData.length <= 1) elementData = Arrays.copyOf(elementData, elementData.length + 1); else elementData = Arrays.copyOf(elementData, elementData.length + (elementData.length >> 1)); //删除元素 public void remove(Object obj) //先查找第一次出现的索引 int i = indexOf(obj); if (i != -1) remove(i); //删除指定索引位置元素 public void remove(int index) if (index < 0 || index > size) throw new IndexOutOfBoundsException("参数越界"); //遍历数组 //for(int i = index;i<elementData.length;i++) // elementData[i]=elementData[i+1]; // System.arraycopy(elementData, index + 1, elementData, index, size - index - 1); size--; //指定索引插入元素 public void insert(int index, Object obj) if (index < 0 || index > size) throw new IndexOutOfBoundsException("参数越界"); // if (size >= elementData.length) this.grown(); //[1,2,3,4][1,2,5,3,4]第一种方式 // System.arraycopy(elementData,index, elementData,index-1,size-index); //遍历数组 for (int i = size - 1; i >= index; i--) elementData[i + 1] = elementData[i]; //将需要插入元素放入指定索引位置 elementData[index] = obj; size++; //查找元素第一次索引 public int indexOf(Object obj) for (int i = 0; i < size; i++) if (elementData[i] == obj || elementData[i] != null && elementData[i].equals(obj)) return i; return -1; //更改元素 public void set(int index, Object obj) elementData[index] = obj; //清空数据 public void clear() elementData = new Object[0]; size = 0; //判断索引是否越界 public boolean out(int index) if (index < 0 || index > size) return false; else return true; //判断是否包含 public boolean contains(Object obj) return indexOf(obj) != -1; //判断是否为空 public boolean isEmpty() return size == 0; //截取子列表 public MyArryList sublist(int fromIndex, int toIdex) if (fromIndex < 0 || toIdex > size) throw new IndexOutOfBoundsException("越界"); if (fromIndex > toIdex) throw new IllegalArgumentException(); MyArryList sublist = new MyArryList(toIdex - fromIndex); System.arraycopy(elementData, fromIndex, sublist, 0, toIdex - fromIndex); sublist.size = toIdex - fromIndex; return sublist; //toString重写 @Override public String toString() Object[] newstring =new Object[size]; System.arraycopy(elementData, 0, newstring, 0, size); return Arrays.toString(newstring);