package com.atguigu.structure;
public class Demo02_arrayList {
public static void main(String[] args) {
MyGenericArrayListV1 arrayListV1 = new MyGenericArrayListV1();
//arr.add(element:100,index:1);下标越界，无法插入
arrayListV1.add(10, 0);
arrayListV1.add(20, 1);
arrayListV1.add(30, 2);
arrayListV1.print();//10 20 30 0 0
arrayListV1.add(40,0);
arrayListV1.add(50,0);
arrayListV1.print();//50 40 10 20 30
arrayListV1.printRev();//30 20 10 40 50
//移除index=0数据前 elements=[50,40,10,20,30] size=5
arrayListV1.remove(0);
//移除index=0数据后 elements=[40,10,20,30,30] size=4
//头插前 elements=[40,10,20,30,30] size=4
arrayListV1.addFirst(50);
//头插后 elements=[50,40,10,20,30] size=5
//移除index=4数据前 elements=[50.40,10,20,30] size=5
arrayListV1.remove(4);
//移除index=4数据后 elements=[50,40,10,20,30] size=4
//尾插前 size=4 elements=[50,40,10,20,30]
arrayListV1.addLast(30);
//尾插后 size=5 elements=[50,40,10,20,30]
//修改index=0数据前 elements=[50,40,10,20,30] size=5
arrayListV1.update(100, 0);
//修改index=0数据后 elements=[100,40,10,20,30] size=5
//查询index=0数据 elements=[100,40,10,20,30] size=5
arrayListV1.get(0);
}
}
class MyGenericArrayListV1{
//组织存储数据的结构
private int[] elements;
//数据关系的属性
//The size of the ArrayList (the number of elements it contains)
//ArrayList集合的大小(包含元素的数量)
private int size;
public MyGenericArrayListV1() {
this(5);
}
public MyGenericArrayListV1(int capacity) {
elements = new int[capacity];
size = 0;
}
//操作数据的方法：
//1、新增：根据下标插入数据、头插 、 尾插
public void addFirst(int element) {
//element=50 elements=[40,10,20,30,30] size=4
this.add(element, 0);
//element=50 elements=[50,40,10,20,30] size=5
}
public void addLast(int element) {
//尾插前 element=30 size=4 elements=[50,40,10,20,30]
this.add(element, size);
//尾插后 element=30 size=5 elements=[50,40,10,20,30]
}
public void add(int element, int index) {//参数1：要新增的数据 参数2：要插入的位置下标
//头插前 element=50 index=0 size=4 elements=[40,10,20,30,30]
//尾插前 element=30 index=4 size=4 elements=[50,40,10,20,30]
if (isFull()) {
System.out.println("数组已满，无法插入");
return;
}
//数组数据是连续存储的，不能跳过未存储数据的位置
//头插前 index=0 size=4 element=50 elements=[40,10,20,30,30]
//尾插前 index=4 size=4 element=30 elements=[50,40,10,20,30]
if (index<0||index>size) {
System.out.println("下标越界，无法插入");
return;
}
//如果新增时，数组中没有元素，添加到第一个索引位置 直接存入
//如果位置上已存在元素 当前索引位置旧元素需要往后移动
//[1,2,3,4,0] => 将 5 插入到索引为 index(1) 的位置 [1,5,2,3,4] ==>设置5到索引1位置
//[1,2,3,0,0] => 将 5 插入到索引为 index(1) 的位置 [1,5,2,3,0] ==>设置5到索引1位置
//判断要存入的位置是否需要移动元素
//index=0 size=4 3>0 满足条件，进入循环 element=50 elements=[40,10,20,30,30]
//index=0 size=4 i=3 elements=[40,10,20,30,30]
//index=0 size=4 i=2 elements=[40,10,20,20,30]
//index=0 size=4 i=1 elements=[40,10,10,20,30]
//index=0 size=4 i=0 elements=[40,40,10,20,30]
//尾插前 index=4 size=4 3>4 不满足条件，循环进不去 elements=[50,40,10,20,30]
for (int i = size - 1; i >= index; i--) {
//i=3 elements=[40,10,20,30,30] elements[3]=30 elements[4]=30
//i=2 elements=[40,10,20,30,30] elements[2]=20 elements[3]=30
//i=1 elements=[40,10,20,20,30] elements[1]=10 elements[2]=20
//i=0 elements=[40,10,10,20,30] elements[0]=40 elements[1]=10
elements[i + 1] = elements[i];
}
//头插前 element=50 index=0 elements=[40,40,10,20,30] size=4 elements[0]=40
//尾插前 element=30 index=4 elements=[50,40,10,20,30] size=4 elements[4]=30
elements[index] = element;
//头插后 size=4 elements=[50,40,10,20,30] element=50 index=0
//尾插后 size=4 elements=[50,40,10,20,30] element=30 index=4
size++;
//头插 size=5 element=50 index=0 elements=[50,40,10,20,30]
//尾插 size=5 element=30 index=4 elements=[50,40,10,20,30]
}
//2、删除
public Integer remove(int index) {
//移除index=0数据前 size=5 isEmpty返回false进不去if
//移除index=4数据前 size=5 elements=[50,40,10,20,30]
if (isEmpty()) {
System.out.println("数组为空，删除失败");
return null;
}
//移除index=0数据前 size=5 elements[0]=50 elements=[50,40,10,20,30]
//移除index=4数据前 size=5 elements[4]=30 elements=[50,40,10,20,30]
if (index < 0 || index >= size) {
System.out.println("下标越界。删除失败");
return null;
}
//移除index=0数据前 index=0 elements=[50,40,10,20,30] elements[0]=50
//移除index=4数据前 index=4 elements=[50,40,10,20,30] elements[4]=30
int remE = elements[index];
//将它后面的元素前移
//移除index=0数据前 index=0 size=5 elements=[50,40,10,20,30] elements[0]=50
//移除index=0数据后 index=0 size=5 elements=[40,40,10,20,30] elements[0]=40
// index=0 i=1 size=5 elements=[40,10,10,20,30] elements[1]=10
// index=0 i=2 size=5 elements=[40,10,20,20,30] elements[2]=20
// index=0 i=3 size=5 elements=[40,10,20,30,30] elements[3]=30
//移除index=4数据前 index=4 size=5 elements=[50,40,10,20,30] remE=30 进不去循环
for (int i = index; i < size - 1; i++) {
//移除index=0数据前 i=0 elements=[50,40,10,20,30] elements[0]=50 elements[1]=40
//移除index=0数据后 i=1 elements=[40,40,10,20,30] elements[1]=40 elements[2]=10
// i=2 elements=[40,10,10,20,30] elements[2]=50 elements[3]=20
// i=3 elements=[40,10,20,20,30] elements[3]=20 elements[4]=30
elements[i] = elements[i + 1];
}
//size记录了元素个数：遍历获取数据使用size作为边界
//移除index=0数据 size=5 remE=50 elements=[40,10,20,30,30]
//移除index=4数据 size=5 remE=30 elements=[50,40,10,20,30]
size--;
//移除index=0数据 size=4 remE=50 elements=[40,10,20,30,30]
//移除index=4数据 size=4 remE=30 elements=[50,40,10,20,30]
return remE;
}
//3、修改
public Integer update(int element, int index) {
//修改index=0数据前 element=100 index=0 size=5
if (isEmpty()) {
System.out.println("数组为空，无法修改");
return null;
}
//修改index=0数据前 size=5 elements=[50,40,10,20,30] element[0]=50
if (index < 0 || index >= size) {
System.out.println("下标越界，无法修改");
return null;
}
//修改index=0数据前 element=100 elements=[50,40,10,20,30] elements[0]=50
int oldE = this.elements[index];
//修改index=0数据前 element=100 elements=[50,40,10,20,30] oldE=50 elements[0]=50
this.elements[index] = element;
//修改index=0数据前 oldE=50 elements=[100,40,10,20,30] elements[0]=100
return oldE;
}
//4、查询
public Integer get(int index) {
//查询index=0数据前 size=5 elements=[100,40,10,20,30]
if (isEmpty()) {
System.out.println("数组为空");
return null;
}
//查询index=0数据前 size=5 elements[0]=100 elements=[100,40,10,20,30]
if (index < 0 || index >= size) {
System.out.println("下标越界，查询失败");
return null;
}
//查询index=0数据后 elements=[100,40,10,20,30] elements[0]=100 size=5
return this.elements[index];
}
//辅助方法：新增数据时size++，移除数据时size--
//是否为空
public boolean isEmpty() {
//移除index=0数据前 size=5 不等于0 方法返回false
//移除index=4数据前 size=5 不等于0 方法返回false
//修改index=0数据前 size=5 不等于0 方法返回false
//查询index=0数据前 size=5 不等于0 方法返回false
return size == 0;
}
//是否已满
public boolean isFull() {
//头插前 elements=[40,10,20,30,30] size=4 elements.length=5
//尾插前 elements=[50,40,10,20,30] size=4 elements.length=5
return size == this.elements.length;
}
//正序打印
public void print() {
if (isEmpty()) {
return;
}
for (int i = 0; i < this.size; i++) {
System.out.print(this.elements[i] + "\t");
}
System.out.println();
}
//反序打印
public void printRev() {
if (isEmpty()) {
return;
}
int length = size;
while (--length >= 0) {//第一次使用数组长度-1，当做下标取最后一个位置的元素打印
//第二次使用长度-2
System.out.print(this.elements[length]+"\t");
}
System.out.println();
}
}
