(Java数据结构)ArrayList

旧城等待， 2024-04-06 10:16 66阅读 0赞

#### 文章目录 ####

*  ArrayList的构造方法
 *   *  ArrayList()
     *  ArrayList(int initialCapacity)
     *  ArrayList(Collection<? extends E> c)
 *  ArrayList的操作
 *   *  remove()
     *  subList()
     *  ArrayList的遍历
     *   *  Iterator.remove()
 *  练习题
 *   *  1.
     *  2.
     *  3.简单的洗牌算法
     *   *  买牌：
         *  洗牌：
         *  揭牌
     *  4.杨辉三角

## ArrayList的构造方法 ##

![在这里插入图片描述][924b860452384f7daf6871305ac973cf.png]

### ArrayList() ###

ArrayList()
    ArrayList<Integer> arrayList1=new ArrayList<>();

![在这里插入图片描述][7ea6f389946e45cb952ae1cf838d82fb.png]

> 调用无参构造方法时，是没有分配内存的，那么数据是怎么放进去？

![在这里插入图片描述][6d29c232daf14803a34f2a41cdba4d00.png]

> 在调用无参构造方法，第一次调用add方法后，容量变成10

> 问题：add第11个的时候是怎么扩容的？

![在这里插入图片描述][31632a4dd6a844f8bf1639068b923e76.png]

### ArrayList(int initialCapacity) ###

![在这里插入图片描述][aea106c5429b453686644eff1b8722dc.png]

ArrayList(int initialCapacity) 
    ArrayList<Integer> arrayList2=new ArrayList<>(12);

### ArrayList(Collection<? extends E> c) ###

ArrayList(Collection<? extends E> c) 
    ？只能传E或E的子类
    ArrayList,并且实现了Collection接口的都可以,如LinkedList
    例：
    ArrayList<String> arrayList4=new ArrayList<>();
    ArrayList<Integer> arrayList3=new ArrayList<>(arrayList4);
    //err
    //String不是Integer的子类

![在这里插入图片描述][fe7c1fc4bba24fe29a8b66f9239ae0cd.png]

## ArrayList的操作 ##

### remove() ###

![在这里插入图片描述][95dd4b890a7047129b4ceadc4829eaec.png]

ArrayList<Integer> arrayList1=new ArrayList<>();
    arrayList1.add(1);
    arrayList1.add(0,7);
    System.out.println(arrayList1);
    arrayList1.remove(new Integer(7));//引用类型
    System.out.println(arrayList1);

[7, 1]
    [1]

### subList() ###

List<E> subList(int fromIndex, int toIndex) 
    //左闭右开

public static void main(String[] args) {
        
            ArrayList<Integer> arrayList1=new ArrayList<>();
            arrayList1.add(1);
            arrayList1.add(2);
            arrayList1.add(3);
            arrayList1.add(4);
            arrayList1.add(5);
            List<Integer> ret=arrayList1.subList(1,3);
            System.out.println(ret);
    }

[2, 3]

ret.set(0,99);
    System.out.println(arrayList1);
    System.out.println(ret);

[1, 99, 3, 4, 5]
    [99, 3]

> 截取没有创建新数组，在原数组基础上修改

### ArrayList的遍历 ###

//使用迭代器
    ArrayList<Integer> arrayList1=new ArrayList<>();
    arrayList1.add(1);
    arrayList1.add(2);
    arrayList1.add(3);
    arrayList1.add(4);
    arrayList1.add(5);
    Iterator<Integer> it=arrayList1.iterator();
    //或Iterator<Integer> it = list.listIterator();
    //因为interface ListIterator<E> extends Iterator<E>
    while(it.hasNext()){
        
        System.out.print(it.next()+" ");
    }
    System.out.println();

1 2 3 4 5

![在这里插入图片描述][eb6632ef75344da2b54971ac3b340c56.png]

#### Iterator.remove() ####

Iterator<Integer> it2=arrayList1.listIterator();
            while(it2.hasNext()){
        
                Integer i=it2.next();
                if(i==3) {
        
                    it2.remove();
                }
            }
            System.out.println(arrayList1);

[1, 2, 4, 5]

## 练习题 ##

### 1. ###

1.一个班有3名学生，这些学生的信息有姓名，年龄，分数。一直每个学生对象都在ArrayList当中存放，请输出每个学生的信息

import java.util.ArrayList;
    
    class Student{
        
        private String name;
        private int age;
        private double score;
    
        public String getName() {
        
            return name;
        }
    
        public void setName(String name) {
        
            this.name = name;
        }
    
        public int getAge() {
        
            return age;
        }
    
        public void setAge(int age) {
        
            this.age = age;
        }
    
        public double getScore() {
        
            return score;
        }
    
        public void setScore(double score) {
        
            this.score = score;
        }
    
        public Student(String name, int age, double score) {
        
            this.name = name;
            this.age = age;
            this.score = score;
        }
    
        @Override
        public String toString() {
        
            return "Student{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    ", score=" + score +
                    '}';
        }
    }
    public class Test {
        
        public static void main(String[] args) {
        
    
            ArrayList<Student> arrayList=new ArrayList<>();
            arrayList.add(new Student("小王",10,19.9));
            arrayList.add(new Student("小宏",20,59.9));
            arrayList.add(new Student("小张",15,89.9));
            for (Student s:
                 arrayList) {
        
                System.out.println(s);
            }
    
        }
    }

对分数进行排序
    class Student implements Comparable<Student> {
        
    @Override
        public int compareTo(Student o) {
        
            return (int)(this.score-o.score);
        }
    }
    public static void main(String[] args) {
        
    Collections.sort(arrayList);
            for (Student s:
                    arrayList) {
        
                System.out.println(s);
            }
    }

> 总结：1.可以指定存放自定义的类，2.可以对集合进行排序

### 2. ###

2.给你两个字符串，str1:"welcome to xx"  str2:"come"
    请删除第一个字符串当中，出现的第二个字符串当中的字符。
    结果：wl t xx
    要求：请使用集合来完成，ArrayList

public static ArrayList<Character> func(String s1,String s2){
        
                ArrayList<Character> arrayList=new ArrayList<>();
            for (int i = 0; i < s1.length(); i++) {
        
                char ch=s1.charAt(i);
                if(!s2.contains(ch+"")){
        
                    arrayList.add(ch);
                }
            }
            return arrayList;
        }
    
        public static void main(String[] args) {
        
            String str1="welcome to xx";
            String str2="come";
            ArrayList<Character> ret=func(str1,str2);
            for (int i = 0; i < ret.size(); i++) {
        
                System.out.print(ret.get(i));
            }
            System.out.println();
        }

### 3.简单的洗牌算法 ###

> 去掉大小王，有52张牌，4个花色，每个花色13张牌

#### 买牌： ####

//首先创建一个牌类
    public class Poker {
        
        private String suit;
        private int rank;
    
        public Poker(String suit, int rank) {
        
            this.suit = suit;
            this.rank = rank;
        }
    
        public String getSuit() {
        
            
            return suit;
        }
    
        public void setSuit(String suit) {
        
            
            this.suit = suit;
        }
    
        public int getRank() {
        
            
            return rank;
        }
    
        public void setRank(int rank) {
        
            
            this.rank = rank;
        }
    
        @Override
        public String toString() {
        
            
            return suit+" "+rank;
        }
    }

public class Pokers {
        
        public static final String[] SUITS={
        "♥","♠","♣","♦"};
        public static List<Poker> buyPokers(){
        
            List<Poker> pokerList=new ArrayList<>();
            for (int i = 0; i < 4; i++) {
        
                for (int j = 1; j <=13; j++) {
        
                    String suit=SUITS[i];
                    Poker poker=new Poker(suit,j);
                    pokerList.add(poker);
                }
            }
            return pokerList;
        }
        public static void main(String[] args) {
        
            List<Poker> pokerList=buyPokers();
            System.out.println("买牌:"+pokerList);
            shuffle(pokerList);
            }
    }

#### 洗牌： ####

> 把有序的牌打乱

public static void shuffle(List<Poker> pokerList){
        
            Random random=new Random();
            for (int i = pokerList.size()-1; i>0; i--) {
        
                int index=random.nextInt(i);
                //生成随机数，[0,i)和i交换
                swap(pokerList,i,index);
            }
        }
    public static void swap(List<Poker> pokerList,int i,int j){
        
            Poker tmp=pokerList.get(i);
            pokerList.set(i,pokerList.get(j));
            pokerList.set(j,tmp);
        }

#### 揭牌 ####

> 有3个人轮流揭牌，有5轮，最后3个人手里都有5张牌  
> 类似于二维数组，3个人的手是一个数组，每一个手要存放5张牌也是一个数组。

List<Poker> hand1=new ArrayList<>();
            List<Poker> hand2=new ArrayList<>();
            List<Poker> hand3=new ArrayList<>();
            List<List<Poker>> hand=new ArrayList<>();
            hand.add(hand1);
            hand.add(hand2);
            hand.add(hand3);
            for (int i = 0; i < 5; i++) {
        
                for (int j = 0; j < 3; j++) {
        
                    List<Poker> handTmp=hand.get(j);
                    handTmp.add(pokerList.remove(0));
                    //E remove(int index);返回值是删除的那个元素
                }
            }
            for (int i = 0; i < 3; i++) {
        
                System.out.println("第"+(i+1)+"个人的牌："+hand.get(i));
            }
            System.out.println("剩余的牌："+pokerList);

> Java ArrayList remove() 方法  
> // 删除指定元素  
> arraylist.remove(Object obj)  
> // 删除指定索引位置的元素  
> arraylist.remove(int index)  
> 返回值  
> 如果传入元素，删除成功，则返回 true。  
> 如果传入索引值，则返回删除的元素。

买牌:[♥ 1, ♥ 2, ♥ 3, ♥ 4, ♥ 5, ♥ 6, ♥ 7, ♥ 8, ♥ 9, ♥ 10, ♥ 11, ♥ 12, ♥ 13, ♠ 1, ♠ 2, ♠ 3, ♠ 4, ♠ 5, ♠ 6, ♠ 7, ♠ 8, ♠ 9, ♠ 10, ♠ 11, ♠ 12, ♠ 13, ♣ 1, ♣ 2, ♣ 3, ♣ 4, ♣ 5, ♣ 6, ♣ 7, ♣ 8, ♣ 9, ♣ 10, ♣ 11, ♣ 12, ♣ 13, ♦ 1, ♦ 2, ♦ 3, ♦ 4, ♦ 5, ♦ 6, ♦ 7, ♦ 8, ♦ 9, ♦ 10, ♦ 11, ♦ 12, ♦ 13]
    洗牌:[♦ 6, ♠ 11, ♦ 10, ♠ 13, ♥ 13, ♦ 12, ♦ 5, ♥ 7, ♠ 1, ♦ 1, ♠ 7, ♣ 5, ♠ 6, ♥ 1, ♣ 12, ♠ 4, ♠ 12, ♠ 9, ♠ 10, ♥ 9, ♥ 2, ♠ 8, ♣ 1, ♦ 2, ♥ 8, ♠ 3, ♠ 2, ♦ 3, ♥ 10, ♦ 13, ♦ 9, ♥ 12, ♣ 3, ♦ 11, ♦ 8, ♥ 5, ♦ 4, ♣ 11, ♦ 7, ♥ 11, ♣ 7, ♣ 8, ♣ 4, ♣ 9, ♥ 4, ♣ 6, ♥ 6, ♥ 3, ♣ 10, ♣ 13, ♣ 2, ♠ 5]
    第1个人的牌：[♦ 6, ♠ 13, ♦ 5, ♦ 1, ♠ 6]
    第2个人的牌：[♠ 11, ♥ 13, ♥ 7, ♠ 7, ♥ 1]
    第3个人的牌：[♦ 10, ♦ 12, ♠ 1, ♣ 5, ♣ 12]
    剩余的牌：[♠ 4, ♠ 12, ♠ 9, ♠ 10, ♥ 9, ♥ 2, ♠ 8, ♣ 1, ♦ 2, ♥ 8, ♠ 3, ♠ 2, ♦ 3, ♥ 10, ♦ 13, ♦ 9, ♥ 12, ♣ 3, ♦ 11, ♦ 8, ♥ 5, ♦ 4, ♣ 11, ♦ 7, ♥ 11, ♣ 7, ♣ 8, ♣ 4, ♣ 9, ♥ 4, ♣ 6, ♥ 6, ♥ 3, ♣ 10, ♣ 13, ♣ 2, ♠ 5]

### 4.杨辉三角 ###

> 类似于二维数组

![在这里插入图片描述][a008e8b05c8248bb982369d73a473e02.png]

class Solution {
        
        public List<List<Integer>> generate(int numRows) {
        
            List<List<Integer>> ret=new ArrayList<List<Integer>>();
            for(int i=0;i<numRows;++i){
        
                List<Integer> row=new ArrayList<>();
                for(int j=0;j<=i;++j){
        
                    if(j==0||j==i){
        
                        row.add(1);
                    }else{
        
                        int num=ret.get(i-1).get(j)+ret.get(i-1).get(j-1);
                        row.add(num);
                    }
                }
                ret.add(row);
            }
            return ret;
        }
    }

> for循环里面定义的变量循环外面用不了

![在这里插入图片描述][8f92523c959a49b2bb23e3c26a612d69.png]

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