javaSE第十八天

Posted 2020-08-09

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第十八天????192

1:Map(掌握)????192

(1)定义：????192

(2)Map和Collection的区别?????192

(3)Map接口功能概述(自己补齐)????192

J:Map集合的遍历方式二entrySet????197

(4)Map集合的遍历????198

(5)HashMap集合的练习????199

A:HashMap<String,String>????199

B:HashMap<Integer,String>????200

C:HashMap<String,Student>????201

1:Student.java文件????201

2:HashMapDemo3.java????203

D:HashMap<Student,String>????203

E:LinkedHashMap的简介????204

(6)TreeMap集合的练习????205

允许value值为null，不允许key值为null ????205

A:TreeMap<String,String>????205

B:TreeMap<Student,String>????206

1:Student.java????206

2:TreeMapDemo2.java????207

(7)案例????208

A:统计一个字符串中每个字符出现的次数????208

B:集合的嵌套遍历????210

a:HashMap嵌套HashMap????210

b:HashMap嵌套ArrayList????211

c:ArrayList嵌套HashMap????212

d:多层嵌套????213

2:Collections(理解)????216

(1)是针对集合进行操作的工具类????216

(2)面试题：Collection和Collections的区别????216

(3)常见的几个小方法：????216

F:方法功能演示：????216

(4)案例????218

A:ArrayList集合存储自定义对象的排序????218

1:Student.java文件????218

2:ConnectionsDemo.java文件????219

B:模拟斗地主洗牌和发牌????220

C:模拟斗地主洗牌和发牌并对牌进行排序的原理图解????221

D:模拟斗地主洗牌和发牌并对牌进行排序????222

3：集合大总结????224

第十八天

1:Map(掌握)

????(1)定义：

将键映射到值的对象。一个映射不能包含重复的键；每个键最多只能映射到一个值。

????(2)Map和Collection的区别?

????????A:Map 存储的是键值对形式的元素，键唯一，值可以重复。夫妻对

????????B:Collection 存储的是单独出现的元素，子接口Set元素唯一，子接口List元素可重复。光棍

????(3)Map接口功能概述(自己补齐)

????????A:添加功能

????????????public V put(K key, V value)：添加元素，这个还有另外一个功能

????????????如果键是第一次存储，就直接存储元素，返回null

????????????如果键不是第一次存储，就用值把以前的值替换掉，返回以前的值

????????B:删除功能

????????????public void clear()：移除集合中的所有元素

????????????public V remove(Object key)：根据键删除键值对元素，并把值返回

????????????????????????????????删除不存在的键，返回null

????????C:判断功能

????????????public boolean containsKey(Object key)：判断集合是否包含指定的键

????????????public boolean containsValue(Object value)判断集合是否包含指定的值

????????????public boolean isEmpty()：判断集合是否为空

????????D:获取功能

????????????Set<Map.Entry<K, V>> entrySet()

????????????public V get(Object key)：根据键获取值

????????????public Set<K> keySet()：获取集合中所有键的集合

????????????public Collection<V> values()：获取集合中所有值的集合

????????E:长度功能

????????????public int size()：返回集合中键值对的对数

????????F:简单方法功能演示：

import java.util.HashMap;

import java.util.Map;

* 作为学生来说，是根据学号来区分不同的学生的，那么假设我现在已经知道了学生的学号，我要根据学号去获取学生姓名，请问怎么做呢?

* 如果采用前面讲解过的集合，我们只能把学号和学生姓名作为一个对象的成员，然后存储整个对象，将来遍历的时候，判断，获取对应的名称。

* 但是呢，如果我都能把学生姓名拿出来了，我还需要根据编号去找吗?

* 针对我们目前的这种需求：仅仅知道学号，就想知道学生姓名的情况，Java就提供了一种新的集合 Map。

* 通过查看API，我们知道Map集合的一个最大的特点，就是它可以存储键值对的元素。这个时候存储我们上面的需求，就可以这样做

* ????????学号1????????姓名1

* ????????学号2 ???? 姓名2

* ????????学号3????????姓名3

* ????????学号2(不行) 姓名4

* ????????学号4 姓名4

* Map集合的特点：

* ????????将键映射到值的对象。一个映射不能包含重复的键；每个键最多只能映射到一个值。

* Map集合和Collection集合的区别?

* ????????Map集合存储元素是成对出现的，Map集合的键是唯一的，值是可重复的。可以把这个理解为：夫妻对

* ????????Collection集合存储元素是单独出现的，Collection的儿子Set是唯一的，List是可重复的。可以把这个理解为：光棍(11.11)

* 注意：

* ????????Map集合的数据结构值针对键有效，跟值无关????

* ????????????HashMap，TreeMap等会讲。

*????????Collection集合的数据结构是针对元素有效

* Map集合的功能概述：

* 1:添加功能

* ????????V put(K key,V value):添加元素。这个其实还有另一个功能?先不告诉你，等会讲

* ????????????如果键是第一次存储，就直接存储元素，返回null

* ????????????如果键不是第一次存在，就用值把以前的值替换掉，返回以前的值

* 2:删除功能

* ????????void clear():移除所有的键值对元素

* ????????V remove(Object key)：根据键删除键值对元素，并把值返回

* 3:判断功能

* ????????boolean containsKey(Object key)：判断集合是否包含指定的键

* ????????boolean containsValue(Object value):判断集合是否包含指定的值

* ????????boolean isEmpty()：判断集合是否为空

* 4:获取功能

* ????????Set<Map.Entry<K,V>> entrySet():???

* ????????V get(Object key):根据键获取值

* ????????Set<K> keySet():获取集合中所有键的集合

* ????????Collection<V> values():获取集合中所有值的集合

* 5：长度功能

* ????????int size()：返回集合中的键值对的对数

class MapDemo {

????public?static?void main(String[] args) {

????????// 创建集合对象

????????Map<String, String> map = new HashMap<String, String>();

????????// 添加元素

????????// V put(K key,V value):添加元素。这个其实还有另一个功能?先不告诉你，等会讲

????????// System.out.println("put:" + map.put("文章", "马伊俐"));//map.put(),第一次存储V，V返回null

????????// System.out.println("put:" + map.put("文章", "姚笛"));//map.put(),第二次存储V，V替换，返回原来的V

????????map.put("邓超", "孙俪");

????????map.put("黄晓明", "杨颖");

????????map.put("周杰伦", "蔡依林");

????????map.put("刘恺威", "杨幂");

????????// void clear():移除所有的键值对元素

????????// map.clear();

????????// V remove(Object key)：根据键删除键值对元素，并把值返回

????????// System.out.println("remove:" + map.remove("黄晓明"));//返回杨颖

????????// System.out.println("remove:" + map.remove("黄晓波"));//删除不存在的键，返回null

????????// boolean containsKey(Object key)：判断集合是否包含指定的键

????????// System.out.println("containsKey:" + map.containsKey("黄晓明"));//true

????????// System.out.println("containsKey:" + map.containsKey("黄晓波"));//false

????????// boolean isEmpty()：判断集合是否为空

????????// System.out.println("isEmpty:"+map.isEmpty());

????????

????????//int size()：返回集合中的键值对的对数

????????System.out.println("size:"+map.size());

????????// 输出集合名称

????????System.out.println("map:" + map);

????}

}

????????G:获取功能演示：

import java.util.Collection;

import java.util.HashMap;

import java.util.Map;

import java.util.Set;

* 获取功能：

* V get(Object key):根据键获取值，如果没有该键，就返回null

* Set<K> keySet():获取集合中所有键的集合

* Collection<V> values():获取集合中所有值的集合

class MapDemo2 {

????public?static?void main(String[] args) {

????????// 创建集合对象

????????Map<String, String> map = new HashMap<String, String>();

????????// 创建元素并添加元素

????????map.put("邓超", "孙俪");

????????map.put("黄晓明", "杨颖");

????????map.put("周杰伦", "蔡依林");

????????map.put("刘恺威", "杨幂");

????????// V get(Object key):根据键获取值

????????System.out.println("get:" + map.get("周杰伦"));//蔡依林

????????System.out.println("get:" + map.get("周杰")); // 返回null

????????System.out.println("----------------------");

????????// Set<K> keySet():获取集合中所有键的集合

????????Set<String> set = map.keySet();//set是键的集合

????????for (String key : set) {

????????????System.out.println(key);

????????}

????????System.out.println("----------------------");

????????// Collection<V> values():获取集合中所有值的集合

????????Collection<String> con = map.values();//con是值的集合

????????for (String value : con) {

????????????System.out.println(value);

????????}

????}

}

????????H:Map集合的遍历方式一

import java.util.HashMap;

import java.util.Map;

import java.util.Set;

* Map集合的遍历。

* Map -- 夫妻对

* 思路：

* ????????A:把所有的丈夫给集中起来。

* ????????B:遍历丈夫的集合，获取得到每一个丈夫。

* ????????C:让丈夫去找自己的妻子。

* 转换：

* ????????A:获取所有的键

* ????????B:遍历键的集合，获取得到每一个键

* ????????C:根据键去找值

class MapDemo3 {

????public?static?void main(String[] args) {

????????// 创建集合对象

????????Map<String, String> map = new HashMap<String, String>();

????????// 创建元素并添加到集合

????????map.put("杨过", "小龙女");

????????map.put("郭靖", "黄蓉");

????????map.put("杨康", "穆念慈");

????????map.put("陈玄风", "梅超风");

????????// 遍历

????????// 获取所有的键

????????Set<String> set = map.keySet();

????????// 遍历键的集合，获取得到每一个键

????????for (String key : set) {

????????????// 根据键去找值

????????????String value = map.get(key);

????????????System.out.println(key + "---" + value);

????????}

????}

}

????????J:Map集合的遍历方式二entrySet

import java.util.HashMap;

import java.util.Map;

import java.util.Set;

* Map集合的遍历。

* Map -- 夫妻对

* 思路：

* ????????A:获取所有结婚证的集合

* ????????B:遍历结婚证的集合，得到每一个结婚证

* ????????C:根据结婚证获取丈夫和妻子

* 转换：

* ????????A:获取所有键值对对象的集合

* ????????B:遍历键值对对象的集合，得到每一个键值对对象

* ????????C:根据键值对对象获取键和值

* 这里面最麻烦的就是键值对对象如何表示呢?

* 看看我们开始的一个方法：

* ????????Set<Map.Entry<K,V>> entrySet()：返回的是键值对对象的集合

class MapDemo4 {

????public?static?void main(String[] args) {

????????// 创建集合对象

????????Map<String, String> map = new HashMap<String, String>();

????????// 创建元素并添加到集合

????????map.put("杨过", "小龙女");

????????map.put("郭靖", "黄蓉");

????????map.put("杨康", "穆念慈");

????????map.put("陈玄风", "梅超风");

????????// 获取所有键值对对象的集合

????????Set<Map.Entry<String, String>> set = map.entrySet();

????????// 遍历键值对对象的集合，得到每一个键值对对象

????????for (Map.Entry<String, String> me : set) {

????????????// 根据键值对对象获取键和值

????????????String key = me.getKey();

????????????String value = me.getValue();

????????????System.out.println(key + "---" + value);

????????}

????}

}

????(4)Map集合的遍历

A:Map集合遍历两种方式比较图解

技术分享

????????B:键找值

????????????a:获取所有键的集合

????????????b:遍历键的集合,得到每一个键

????????????c:根据键到集合中去找值

????????

????????C:键值对对象找键和值

????????????a:获取所有的键值对对象的集合

????????????b:遍历键值对对象的集合，获取每一个键值对对象

????????????c:根据键值对对象去获取键和值

????????????

????????代码体现：

????????????

// 创建集合对象

????????Map<String, String> map = new HashMap<String, String>();

????????// 创建元素并添加到集合

????????map.put("杨过", "小龙女");

????????map.put("郭靖", "黄蓉");

????????map.put("杨康", "穆念慈");

????????map.put("陈玄风", "梅超风");

????????????

????????????//方式1 键找值

????????????

//方式一：键找值

????????Set<String> keys = map.keySet();

????????for(String key : keys) {

????????????String value = map.get(key);

????????????System.out.println(key + "--" + value);

????????}

????????????

????????????//方式2 键值对对象找键和值

????????????

// 方式二：获取所有键值对对象的集合

????????Set<Map.Entry<String, String>> set = map.entrySet();

????????// 遍历键值对对象的集合，得到每一个键值对对象

????????for (Map.Entry<String, String> me : set) {

????????????// 根据键值对对象获取键和值

????????????String key = me.getKey();

????????????String value = me.getValue();

????????????System.out.println(key + "---" + value);

????????}

????(5)HashMap集合的练习

????????????允许插入null-null键值对

????????A:HashMap<String,String>

import java.util.HashMap;

import java.util.Set;

* HashMap:是基于哈希表的Map接口实现。

* 哈希表的作用是用来保证键的唯一性的。

* HashMap<String,String>

* 键：String

* 值：String

class HashMapDemo {

????public?static?void main(String[] args) {

????????// 创建集合对象

????????HashMap<String, String> hm = new HashMap<String, String>();

????????// 创建元素并添加元素

????????

????????hm.put("it001", "马云");

????????hm.put("it003", "马化腾");

????????hm.put("it004", "乔布斯");

????????hm.put("it005", "张朝阳");

????????hm.put("it002", "裘伯君"); // wps

????????hm.put("it001", "比尔盖茨");

????????// 遍历

????????Set<String> set = hm.keySet();

????????for (String key : set) {

????????????String value = hm.get(key);

????????????System.out.println(key + "---" + value);

????????}

????}

}

????????B:HashMap<Integer,String>

import java.util.HashMap;

import java.util.Set;

* HashMap<Integer,String>

* 键：Integer

* 值：String

class HashMapDemo2 {

????public?static?void main(String[] args) {

????????// 创建集合对象

????????HashMap<Integer, String> hm = new HashMap<Integer, String>();

????????// 创建元素并添加元素

????????// Integer i = new Integer(27);

????????// Integer i = 27;

????????// String s = "林青霞";

????????// hm.put(i, s);

????????hm.put(27, "林青霞");

????????hm.put(30, "风清扬");

????????hm.put(28, "刘意");

????????hm.put(29, "林青霞");

????????// 0开头的是八进制数据//下面的写法是八进制，但是不能出现8以上的单个数据

????????// hm.put(003, "hello");

????????// hm.put(006, "hello");

????????// hm.put(007, "hello");

????????// hm.put(008, "hello");

????????// 遍历

????????Set<Integer> set = hm.keySet();

????????for (Integer key : set) {

????????????String value = hm.get(key);

????????????System.out.println(key + "---" + value);

????????}

????????// 下面这种方式仅仅是集合的元素的字符串表示

????????// System.out.println("hm:" + hm);

????}

}

????????C:HashMap<String,Student>

????????????1:Student.java文件

public?class Student {

????private String name;

????private?int?age;

????public Student() {

????????super();

????}

????public Student(String name, int?age) {

????????super();

????????this.name = name;

????????this.age = age;

????}

????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;

????}

????@Override

????public?int hashCode() {

????????final?int?prime = 31;

????????int?result = 1;

????????result = prime * result + age;

????????result = prime * result + ((name == null) ? 0 : name.hashCode());

????????return?result;

????}

????@Override

????public?boolean equals(Object obj) {

????????if (this == obj)

????????????return?true;

????????if (obj == null)

????????????return?false;

????????if (getClass() != obj.getClass())

????????????return?false;

????????Student other = (Student) obj;

????????if (age != other.age)

????????????return?false;

????????if (name == null) {

????????????if (other.name != null)

????????????????return?false;

????????} else?if (!name.equals(other.name))

????????????return?false;

????????return?true;

????}

????????????2:HashMapDemo3.java

import java.util.HashMap;

import java.util.Set;

* HashMap<String,Student>

* 键：String????学号

* 值：Student 学生对象

class HashMapDemo3 {

????public?static?void main(String[] args) {

????????// 创建集合对象

????????HashMap<String, Student> hm = new HashMap<String, Student>();

????????// 创建学生对象

????????Student s1 = new Student("周星驰", 58);

????????Student s2 = new Student("刘德华", 55);

????????Student s3 = new Student("梁朝伟", 54);

????????Student s4 = new Student("刘嘉玲", 50);

????????// 添加元素

????????hm.put("9527", s1);

????????hm.put("9522", s2);

????????hm.put("9524", s3);

????????hm.put("9529", s4);

????????// 遍历

????????Set<String> set = hm.keySet();

????????for (String key : set) {

????????????// 注意了：这次值不是字符串了

????????????// String value = hm.get(key);

????????????Student value = hm.get(key);

????????????System.out.println(key + "---" + value.getName() + "---"

????????????????????+ value.getAge());

????????}

????}

}

????????D:HashMap<Student,String>

import java.util.HashMap;

import java.util.Set;

* HashMap<Student,String>

* 键：Student

* ????????要求：如果两个对象的成员变量值都相同，则为同一个对象。

* 值：String

class HashMapDemo4 {

????public?static?void main(String[] args) {

????????// 创建集合对象

????????HashMap<Student, String> hm = new HashMap<Student, String>();

????????// 创建学生对象

????????Student s1 = new Student("貂蝉", 27);

????????Student s2 = new Student("王昭君", 30);

????????Student s3 = new Student("西施", 33);

????????Student s4 = new Student("杨玉环", 35);

????????Student s5 = new Student("貂蝉", 27);

????????// 添加元素

????????hm.put(s1, "8888");

????????hm.put(s2, "6666");

????????hm.put(s3, "5555");

????????hm.put(s4, "7777");

????????hm.put(s5, "9999");

????????// 遍历

????????Set<Student> set = hm.keySet();

????????for (Student key : set) {

????????????String value = hm.get(key);

????????????System.out.println(key.getName() + "---" + key.getAge() + "---"

????????????????????+ value);

????????}

????}

}

????????E:LinkedHashMap的简介

import java.util.LinkedHashMap;

import java.util.Set;

* LinkedHashMap:是Map接口的哈希表和链接列表实现，具有可预知的迭代顺序。

* 由哈希表保证键的唯一性

* 由链表保证键盘的有序(存储和取出的顺序一致)

class LinkedHashMapDemo {

????public?static?void main(String[] args) {

????????// 创建集合对象

????????LinkedHashMap<String, String> hm = new LinkedHashMap<String, String>();

????????// 创建并添加元素

????????hm.put("2345", "hello");

????????hm.put("1234", "world");

????????hm.put("3456", "java");

????????hm.put("1234", "javaee");

????????hm.put("3456", "android");

????????// 遍历

????????Set<String> set = hm.keySet();

????????for (String key : set) {

????????????String value = hm.get(key);

????????????System.out.println(key + "---" + value);

????????}

????}

}

????(6)TreeMap集合的练习????

???????? 允许value值为null，不允许key值为null ????

????????A:TreeMap<String,String>

import java.util.Set;

import java.util.TreeMap;

* TreeMap:是基于红黑树的Map接口的实现。

* HashMap<String,String>

* 键：String

* 值：String

class TreeMapDemo {

????public?static?void main(String[] args) {

????????// 创建集合对象

????????TreeMap<String, String> tm = new TreeMap<String, String>();

????????// 创建元素并添加元素

????????tm.put("hello", "你好");

????????tm.put("world", "世界");

????????tm.put("java", "爪哇");

????????tm.put("world", "世界2");

????????tm.put("javaee", "爪哇EE");

????????// 遍历集合

????????Set<String> set = tm.keySet();

????????for (String key : set) {

????????????String value = tm.get(key);

????????????System.out.println(key + "---" + value);

????????}

????}

}

????????B:TreeMap<Student,String>

????????????1:Student.java

public?class Student {

????private String name;

????private?int?age;

????public Student() {

????????super();

????}

????public Student(String name, int?age) {

????????super();

????????this.name = name;

????????this.age = age;

????}

????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;

????}

}

????????????2:TreeMapDemo2.java

import java.util.Comparator;

import java.util.Set;

import java.util.TreeMap;

* TreeMap<Student,String>

* 键:Student

* 值：String

class TreeMapDemo2 {

????public?static?void main(String[] args) {

????????// 创建集合对象，用匿名内部类实现比较器排序

????????TreeMap<Student, String> tm = new TreeMap<Student, String>(

????????????????new Comparator<Student>() {

????????????????????@Override

????????????????????public?int compare(Student s1, Student s2) {

????????????????????????// 主要条件

????????????????????????int?num = s1.getAge() - s2.getAge();

????????????????????????// 次要条件

????????????????????????int?num2 = num == 0 ? s1.getName().compareTo(

????????????????????????????????s2.getName()) : num;

????????????????????????return?num2;

????????????????????}

????????????????});

????????// 创建学生对象

????????Student s1 = new Student("潘安", 30);

????????Student s2 = new Student("柳下惠", 35);

????????Student s3 = new Student("唐伯虎", 33);

????????Student s4 = new Student("燕青", 32);

????????Student s5 = new Student("唐伯虎", 33);

????????// 存储元素

????????tm.put(s1, "宋朝");

????????tm.put(s2, "元朝");

????????tm.put(s3, "明朝");

????????tm.put(s4, "清朝");

????????tm.put(s5, "汉朝");

????????// 遍历

????????Set<Student> set = tm.keySet();

????????for (Student key : set) {

????????????String value = tm.get(key);

????????????System.out.println(key.getName() + "---" + key.getAge() + "---"

????????????????????+ value);

????????}

????}

}

????(7)案例

????????A:统计一个字符串中每个字符出现的次数

统计一个字符串中每个字符出现次数图解

技术分享

import java.util.Scanner;

import java.util.Set;

import java.util.TreeMap;

* 需求："aababcabcdabcde",获取字符串中每一个字母出现的次数要求结果:a(5)b(4)c(3)d(2)e(1)

* 分析：

* ????????A:定义一个字符串(可以改进为键盘录入)

* ????????B:定义一个TreeMap集合

* ????????????键:Character

* ????????????值：Integer

* ????????C:把字符串转换为字符数组

* ????????D:遍历字符数组，得到每一个字符

* ????????E:拿刚才得到的字符作为键到集合中去找值，看返回值

* ????????????是null:说明该键不存在，就把该字符作为键，1作为值存储

* ????????????不是null:说明该键存在，就把值加1，然后重写存储该键和值

* ????????F:定义字符串缓冲区变量

* ????????G:遍历集合，得到键和值，进行按照要求拼接

* ????????H:把字符串缓冲区转换为字符串输出

* 录入：linqingxia

* 结果：result:a(1)g(1)i(3)l(1)n(2)q(1)x(1)

class TreeMapDemo {

????public?static?void main(String[] args) {

????????// 定义一个字符串(可以改进为键盘录入)

????????Scanner sc = new Scanner(System.in);

????????System.out.println("请输入一个字符串：");

????????String line = sc.nextLine();

????????// 定义一个TreeMap集合

????????TreeMap<Character, Integer> tm = new TreeMap<Character, Integer>();

????????

????????//把字符串转换为字符数组

????????char[] chs = line.toCharArray();

????????

????????//遍历字符数组，得到每一个字符

????????for(char?ch : chs){

????????????//拿刚才得到的字符作为键到集合中去找值，看返回值

????????????Integer i = tm.get(ch);

????????????

????????????//是null:说明该键不存在，就把该字符作为键，1作为值存储

????????????if(i == null){

????????????????tm.put(ch, 1);

????????????}else {

????????????????//不是null:说明该键存在，就把值加1，然后重写存储该键和值

????????????????i++;

????????????????tm.put(ch,i);

????????????}

????????}

????????

????????//定义字符串缓冲区变量

????????StringBuilder sb= new StringBuilder();

????????

????????//遍历集合，得到键和值，进行按照要求拼接

????????Set<Character> set = tm.keySet();

????????for(Character key : set){

????????????Integer value = tm.get(key);

????????????sb.append(key).append("(").append(value).append(")");

????????}

????????

????????//把字符串缓冲区转换为字符串输出

????????String result = sb.toString();

????????System.out.println("result:"+result);

????}

}

????????B:集合的嵌套遍历

????????????a:HashMap嵌套HashMap

import java.util.HashMap;

import java.util.Set;

* HashMap嵌套HashMap

* 传智播客

* ????????jc????基础班

* ????????????????陈玉楼????????20

* ????????????????高跃????????22

* ????????jy????就业班

* ????????????????李杰????????21

* ????????????????曹石磊????????23

* 先存储元素，然后遍历元素

class HashMapDemo2 {

????public?static?void main(String[] args) {

????????// 创建集合对象

????????HashMap<String, HashMap<String, Integer>> czbkMap = new HashMap<String, HashMap<String, Integer>>();

????????// 创建基础班集合对象

????????HashMap<String, Integer> jcMap = new HashMap<String, Integer>();

????????// 添加元素

????????jcMap.put("陈玉楼", 20);

????????jcMap.put("高跃", 22);

????????// 把基础班添加到大集合

????????czbkMap.put("jc", jcMap);

????????// 创建就业班集合对象

????????HashMap<String, Integer> jyMap = new HashMap<String, Integer>();

????????// 添加元素

????????jyMap.put("李杰", 21);

????????jyMap.put("曹石磊", 23);

????????// 把基础班添加到大集合

????????czbkMap.put("jy", jyMap);

????????

????????//遍历集合

????????Set<String> czbkMapSet = czbkMap.keySet();

????????for(String czbkMapKey : czbkMapSet){

????????????System.out.println(czbkMapKey);

????????????HashMap<String, Integer> czbkMapValue = czbkMap.get(czbkMapKey);

????????????Set<String> czbkMapValueSet = czbkMapValue.keySet();

????????????for(String czbkMapValueKey : czbkMapValueSet){

????????????????Integer czbkMapValueValue = czbkMapValue.get(czbkMapValueKey);

????????????????System.out.println("\t"+czbkMapValueKey+"---"+czbkMapValueValue);

????????????}

????????}

????}

}

????????????b:HashMap嵌套ArrayList

import java.util.ArrayList;

import java.util.HashMap;

import java.util.Set;

*需求：

*假设HashMap集合的元素是ArrayList。有3个。

*每一个ArrayList集合的值是字符串。

*元素我已经完成，请遍历。

*结果：

*???????? 三国演义

*?????????????吕布

*?????????????周瑜

*???????? 笑傲江湖

*?????????????令狐冲

*?????????????林平之

*???????? 神雕侠侣

*?????????????郭靖

*?????????????杨过

class HashMapIncludeArrayListDemo {

????public?static?void main(String[] args) {

????????// 创建集合对象

????????HashMap<String, ArrayList<String>> hm = new HashMap<String, ArrayList<String>>();

????????// 创建元素集合1

????????ArrayList<String> array1 = new ArrayList<String>();

????????array1.add("吕布");

????????array1.add("周瑜");

????????hm.put("三国演义", array1);

????????// 创建元素集合2

????????ArrayList<String> array2 = new ArrayList<String>();

????????array2.add("令狐冲");

????????array2.add("林平之");

????????hm.put("笑傲江湖", array2);

????????// 创建元素集合3

????????ArrayList<String> array3 = new ArrayList<String>();

????????array3.add("郭靖");

????????array3.add("杨过");

????????hm.put("神雕侠侣", array3);

????????

????????//遍历集合

????????Set<String> set = hm.keySet();

????????for(String key : set){

????????????System.out.println(key);

????????????ArrayList<String> value = hm.get(key);

????????????for(String s : value){

????????????????System.out.println("\t"+s);

????????????}

????????}

????}

}

????????????c:ArrayList嵌套HashMap

import java.util.ArrayList;

import java.util.HashMap;

import java.util.Set;

ArrayList集合嵌套HashMap集合并遍历。

需求：

假设ArrayList集合的元素是HashMap。有3个。

每一个HashMap集合的键和值都是字符串。

元素我已经完成，请遍历。

结果：

周瑜---小乔

吕布---貂蝉

郭靖---黄蓉

杨过---小龙女

令狐冲---任盈盈

林平之---岳灵珊

class ArrayListIncludeHashMapDemo {

????public?static?void main(String[] args) {

????????// 创建集合对象

????????ArrayList<HashMap<String, String>> array = new ArrayList<HashMap<String, String>>();

????????// 创建元素1

????????HashMap<String, String> hm1 = new HashMap<String, String>();

????????hm1.put("周瑜", "小乔");

????????hm1.put("吕布", "貂蝉");

????????// 把元素添加到array里面

????????array.add(hm1);

????????// 创建元素1

????????HashMap<String, String> hm2 = new HashMap<String, String>();

????????hm2.put("郭靖", "黄蓉");

????????hm2.put("杨过", "小龙女");

????????// 把元素添加到array里面

????????array.add(hm2);

????????// 创建元素1

????????HashMap<String, String> hm3 = new HashMap<String, String>();

????????hm3.put("令狐冲", "任盈盈");

????????hm3.put("林平之", "岳灵珊");

????????// 把元素添加到array里面

????????array.add(hm3);

????????// 遍历

????????for (HashMap<String, String> hm : array) {

????????????Set<String> set = hm.keySet();

????????????for (String key : set) {

????????????????String value = hm.get(key);

????????????????System.out.println(key + "---" + value);

????????????}

????????}

????}

}

????????????d:多层嵌套

????????????

import java.util.ArrayList;

import java.util.HashMap;

import java.util.Set;

* 多层嵌套

* ????????：hashMap里面嵌套hashmap，hashMap里面在嵌套ArrayList

* 为了更符合要求：

* ????????这次的数据就看成是学生对象。

* 传智播客

* ????????bj????北京校区

* ????????????jc????基础班

* ????????????????????林青霞????????27

* ????????????????????风清扬????????30

* ????????????jy????就业班????

* ????????????????????赵雅芝????????28

* ????????????????????武鑫????????29

* ????????sh????上海校区

* ????????????jc????基础班

* ????????????????????郭美美????????20

* ????????????????????犀利哥????????22

* ????????????jy????就业班????

* ????????????????????罗玉凤????????21

* ????????????????????马征????????23

* ????????gz????广州校区

* ????????????jc????基础班

* ????????????????????王力宏????????30

* ????????????????????李静磊????????32

* ????????????jy????就业班????

* ????????????????????郎朗????????31

* ????????????????????柳岩????????33

* ????????xa????西安校区

* ????????????jc????基础班

* ????????????????????范冰冰????????27

* ????????????????????刘意????????30

* ????????????jy????就业班????

* ????????????????????李冰冰????????28

* ????????????????????张志豪????????29

class HashMapDemo {

????public?static?void main(String[] args) {

????????// 创建大集合

????????HashMap<String, HashMap<String, ArrayList<Student>>> czbkMap = new HashMap<String, HashMap<String, ArrayList<Student>>>();

????????// 北京校区数据

????????HashMap<String, ArrayList<Student>> bjCzbkMap = new HashMap<String, ArrayList<Student>>();

????????ArrayList<Student> array1 = new ArrayList<Student>();

????????Student s1 = new Student("林青霞", 27);

????????Student s2 = new Student("风清扬", 30);

????????array1.add(s1);

????????array1.add(s2);

????????ArrayList<Student> array2 = new ArrayList<Student>();

????????Student s3 = new Student("赵雅芝", 28);

????????Student s4 = new Student("武鑫", 29);

????????array2.add(s3);

????????array2.add(s4);

????????bjCzbkMap.put("基础班", array1);

????????bjCzbkMap.put("就业班", array2);

????????czbkMap.put("北京校区", bjCzbkMap);

????????// 晚上可以自己练习一下

????????// 上海校区数据自己做

????????// 广州校区数据自己做

????????// 西安校区数据

????????HashMap<String, ArrayList<Student>> xaCzbkMap = new HashMap<String, ArrayList<Student>>();

????????ArrayList<Student> array3 = new ArrayList<Student>();

????????Student s5 = new Student("范冰冰", 27);

????????Student s6 = new Student("刘意", 30);

????????array3.add(s5);

????????array3.add(s6);

????????ArrayList<Student> array4 = new ArrayList<Student>();

????????Student s7 = new Student("李冰冰", 28);

????????Student s8 = new Student("张志豪", 29);

????????array4.add(s7);

????????array4.add(s8);

????????xaCzbkMap.put("基础班", array3);

????????xaCzbkMap.put("就业班", array4);

????????czbkMap.put("西安校区", xaCzbkMap);

????????// 遍历集合

????????Set<String> czbkMapSet = czbkMap.keySet();

????????for (String czbkMapKey : czbkMapSet) {

????????????System.out.println(czbkMapKey);

????????????HashMap<String, ArrayList<Student>> czbkMapValue = czbkMap

????????????????????.get(czbkMapKey);

????????????Set<String> czbkMapValueSet = czbkMapValue.keySet();

????????????for (String czbkMapValueKey : czbkMapValueSet) {

????????????????System.out.println("\t" + czbkMapValueKey);

????????????????ArrayList<Student> czbkMapValueValue = czbkMapValue

????????????????????????.get(czbkMapValueKey);

????????????????for (Student s : czbkMapValueValue) {

????????????????????System.out.println("\t\t" + s.getName() + "---"

????????????????????????????+ s.getAge());

????????????????}

????????????}

????????}

????}

}

2:Collections(理解)????

????(1)是针对集合进行操作的工具类

????(2)面试题：Collection和Collections的区别

????????A:Collection 是单列集合的顶层接口，有两个子接口List和Set

????????B:Collections 是针对集合进行操作的工具类，可以对集合进行排序和查找等

????(3)常见的几个小方法：

????????A:public static <T> void sort(List<T> list)：排序，默认情况下是自然排序

????????B:public static <T> void sort(List<T> list, Comparator<? super T> c):按照比较器进行排序

???????????? 说明：如果同时有自然排序和比较器排序，则以比较器排序为主

????????C:public static <T> int binarySearch(List<?> list,T key)：二分查找

????????D:public static <T> T max(Collection<?> coll)：最大值

????????E:public static void reverse(List<?> list)：反转

????????F:public static void shuffle(List<?> list)：随机置换

F:方法功能演示：

????

import java.util.Collections;

import java.util.List;

import java.util.ArrayList;

* Collections:是针对集合进行操作的工具类，都是静态方法。

* 面试题：

* Collection和Collections的区别?

* Collection:是单列集合的顶层接口，有子接口List和Set。

* Collections:是针对集合操作的工具类，有对集合进行排序和二分查找的方法

* 要知道的方法

* public static <T> void sort(List<T> list)：排序默认情况下是自然顺序。

* public static <T> int binarySearch(List<?> list,T key):二分查找

* public static <T> T max(Collection<?> coll):最大值

* public static void reverse(List<?> list):反转

* public static void shuffle(List<?> list):随机置换

class CollectionsDemo {

????public?static?void main(String[] args) {

????????// 创建集合对象

????????List<Integer> list = new ArrayList<Integer>();

????????// 添加元素

????????list.add(30);

????????list.add(20);

????????list.add(50);

????????list.add(10);

????????list.add(40);

????????System.out.println("list:" + list);

????????// public static <T> void sort(List<T> list)：排序默认情况下是自然顺序。

????????// Collections.sort(list);

????????// System.out.println("list:" + list);

????????// [10, 20, 30, 40, 50]

????????// public static <T> int binarySearch(List<?> list,T key):二分查找

????????// System.out

????????// .println("binarySearch:" + Collections.binarySearch(list, 30));

????????// System.out.println("binarySearch:"

????????// + Collections.binarySearch(list, 300));

????????// public static <T> T max(Collection<?> coll):最大值

????????// System.out.println("max:"+Collections.max(list));

????????// public static void reverse(List<?> list):反转

????????// Collections.reverse(list);

????????// System.out.println("list:" + list);

????????

????????//public static void shuffle(List<?> list):随机置换

????????Collections.shuffle(list);

????????System.out.println("list:" + list);

????}

}

????(4)案例

????????A:ArrayList集合存储自定义对象的排序

????????????1:Student.java文件

* 对象自然排序：

* ????????必须实现Comparable接口，重写里面的 compareTo方法

public?class Student implements Comparable<Student> {

????private String name;

????private?int?age;

????public Student() {

????????super();

????}

????public Student(String name, int?age) {

????????super();

????????this.name = name;

????????this.age = age;

????}

????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;

????}

????@Override

????public?int compareTo(Student s) {

????????int?num = this.age - s.age;

????????int?num2 = num == 0 ? this.name.compareTo(s.name) : num;

????????return?num2;

????}

}

????????????2:ConnectionsDemo.java文件

import java.util.ArrayList;

import java.util.Collections;

import java.util.Comparator;

import java.util.List;

* Collections可以针对ArrayList存储基本包装类的元素排序，存储自定义对象可不可以排序呢?

*如果同时有自然排序和比较器排序，以比较器排序为主

class CollectionsDemo {

????public?static?void main(String[] args) {

????????// 创建集合对象

????????List<Student> list = new ArrayList<Student>();

????????// 创建学生对象

????????Student s1 = new Student("林青霞", 27);

????????Student s2 = new Student("风清扬", 30);

????????Student s3 = new Student("刘晓曲", 28);

????????Student s4 = new Student("武鑫", 29);

????????Student s5 = new Student("林青霞", 27);

????????// 添加元素对象

????????list.add(s1);

????????list.add(s2);

????????list.add(s3);

????????list.add(s4);

????????list.add(s5);

????????// 排序

????????// 自然排序

????????// Collections.sort(list);

????????// 比较器排序

????????// 如果同时有自然排序和比较器排序，以比较器排序为主

????????Collections.sort(list, new Comparator<Student>() {

????????????@Override

????????????public?int compare(Student s1, Student s2) {

????????????????int?num = s2.getAge() - s1.getAge();

????????????????int?num2 = num == 0 ? s1.getName().compareTo(s2.getName()) : num;

????????????????return?num2;

????????????}

????????});

????????// 遍历集合

????????for (Student s : list) {

????????????System.out.println(s.getName() + "---" + s.getAge());

????????}

????}

}

????????B:模拟斗地主洗牌和发牌

????????????PokerDemo.java文件

import java.util.ArrayList;

import java.util.Collections;

* 模拟斗地主洗牌和发牌

* 分析：

* ????????A:创建一个牌盒

* ????????B:装牌

* ????????C:洗牌

* ????????D:发牌

* ????????E:看牌

class PokerDemo {

????public?static?void main(String[] args) {

????????// 创建一个牌盒

????????ArrayList<String> array = new ArrayList<String>();

????????// 装牌

????????// 黑桃A,黑桃2,黑桃3,...黑桃K

????????// 红桃A,...

????????// 梅花A,...

????????// 方块A,...

????????// 定义一个花色数组

????????String[] colors = { "?", "?", "?", "?" };

????????// 定义一个点数数组

????????String[] numbers = { "A", "2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K" };

????????// 装牌

????????for (String color : colors) {

????????????for (String number : numbers) {

????????????????array.add(color.concat(number));

????????????}

????????}

????????array.add("小王");

????????array.add("大王");

????????// 洗牌

????????Collections.shuffle(array);

????????// System.out.println("array:" + array);

????????// 发牌

????????ArrayList<String> fengQingYang = new ArrayList<String>();

????????ArrayList<String> linQingXia = new ArrayList<String>();

????????ArrayList<String> liuYi = new ArrayList<String>();

????????ArrayList<String> diPai = new ArrayList<String>();

????????for (int?x = 0; x < array.size(); x++) {

????????????if (x >= array.size() - 3) {

????????????????diPai.add(array.get(x));

????????????} else?if (x % 3 == 0) {

????????????????fengQingYang.add(array.get(x));

????????????} else?if (x % 3 == 1) {

????????????????linQingXia.add(array.get(x));

????????????} else?if (x % 3 == 2) {

????????????????liuYi.add(array.get(x));

????????????}

????????}

????????// 看牌

????????lookPoker("风清扬", fengQingYang);

????????lookPoker("林青霞", linQingXia);

????????lookPoker("刘意", liuYi);

????????lookPoker("底牌", diPai);

????}

????public?static?void lookPoker(String name, ArrayList<String> array) {

????????System.out.print(name + "的牌是：");

????????for (String s : array) {

????????????System.out.print(s + " ");

????????}

????????System.out.println();

????}

}

C:模拟斗地主洗牌和发牌并对牌进行排序的原理图解

技术分享

????????D:模拟斗地主洗牌和发牌并对牌进行排序

????????????PokerDemo.java文件

import?java.util.ArrayList;

import java.util.Collections;

import java.util.HashMap;

import java.util.TreeSet;

* 思路：

* ????????A:创建一个HashMap集合

* ????????B:创建一个ArrayList集合

* ????????C:创建花色数组和点数数组

* ????????D:从0开始往HashMap里面存储编号，并存储对应的牌

* 同时往ArrayList里面存储编号即可。

* E:洗牌(洗的是编号)

* F:发牌(发的也是编号，为了保证编号是排序的，就创建TreeSet集合接收)

* G:看牌(遍历TreeSet集合，获取编号，到HashMap集合找对应的牌)

class PokerDemo {

????public?static?void main(String[] args) {

????????// 创建一个HashMap集合

????????HashMap<Integer, String> hm = new HashMap<Integer, String>();

????????// 创建一个ArrayList集合

????????ArrayList<Integer> array = new?ArrayList<Integer>();

????????// 创建花色数组和点数数组

????????// 定义一个花色数组

????????String[] colors = { "?", "?", "?", "?" };

????????// 定义一个点数数组

????????String[] numbers = { "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A", "2", };

????????// 从0开始往HashMap里面存储编号，并存储对应的牌,同时往ArrayList里面存储编号即可。

????????int?index = 0;

????????for (String number : numbers) {

????????????for (String color : colors) {

????????????????String poker = color.concat(number);

????????????????hm.put(index, poker);

????????????????array.add(index);

????????????????index++;

????????????}

????????}

????????hm.put(index, "小王");

????????array.add(index);

????????index++;

????????hm.put(index, "大王");

????????array.add(index);

????????// 洗牌(洗的是编号)

????????Collections.shuffle(array);

????????// 发牌(发的也是编号，为了保证编号是排序的，就创建TreeSet集合接收)

????????TreeSet<Integer> fengQingYang = new TreeSet<Integer>();

????????TreeSet<Integer> linQingXia = new TreeSet<Integer>();

????????TreeSet<Integer> liuYi = new TreeSet<Integer>();

????????TreeSet<Integer> diPai = new TreeSet<Integer>();

????????for (int?x = 0; x < array.size(); x++) {

????????????if (x >= array.size() - 3) {

????????????????diPai.add(array.get(x));

????????????} else?if (x % 3 == 0) {

????????????????fengQingYang.add(array.get(x));

????????????} else?if (x % 3 == 1) {

????????????????linQingXia.add(array.get(x));

????????????} else?if (x % 3 == 2) {

????????????????liuYi.add(array.get(x));

????????????}

????????}

????????// 看牌(遍历TreeSet集合，获取编号，到HashMap集合找对应的牌)

????????lookPoker("风清扬", fengQingYang, hm);

????????lookPoker("林青霞", linQingXia, hm);

????????lookPoker("刘意", liuYi, hm);

????????lookPoker("底牌", diPai, hm);

????}

????// 写看牌的功能

????public?static?void lookPoker(String name, TreeSet<Integer> ts, HashMap<Integer, String> hm) {

????????System.out.print(name + "的牌是：");

????????for (Integer key : ts) {

????????????String value = hm.get(key);

????????????System.out.print(value + " ");

????????}

????????System.out.println();

????}

}

3：集合大总结

1:集合(自己补齐)

Collection(单列集合)

????List(有序,可重复)

????????ArrayList

????????????底层数据结构是数组,查询快,增删慢

????????????线程不安全,效率高

????????Vector

????????????底层数据结构是数组,查询快,增删慢

????????????线程安全,效率低

????????LinkedList

????????????底层数据结构是链表,查询慢,增删快

????????????线程不安全,效率高

????Set(无序,唯一)

????????HashSet

????????????底层数据结构是哈希表。

????????????哈希表依赖两个方法：hashCode()和equals()

????????????执行顺序：

????????????????首先判断hashCode()值是否相同

????????????????????是：继续执行equals(),看其返回值

????????????????????????是true:说明元素重复，不添加

????????????????????????是false:就直接添加到集合

????????????????????否：就直接添加到集合

????????????最终：

????????????????自动生成hashCode()和equals()即可

????????????????

????????????LinkedHashSet

????????????????底层数据结构由链表和哈希表组成。

????????????????由链表保证元素有序。

????????????????由哈希表保证元素唯一。

????????TreeSet

????????????底层数据结构是红黑树。(是一种自平衡的二叉树)

????????????如何保证元素唯一性呢?

????????????????根据比较的返回值是否是0来决定

????????????如何保证元素的排序呢?

????????????????两种方式

????????????????????自然排序(元素具备比较性)

????????????????????????让元素所属的类实现Comparable接口

????????????????????比较器排序(集合具备比较性)

????????????????????????让集合接收一个Comparator的实现类对象

Map(双列集合)

????A:Map集合的数据结构仅仅针对键有效，与值无关。

????B:存储的是键值对形式的元素，键唯一，值可重复。

????

????HashMap

????????底层数据结构是哈希表。线程不安全，效率高

????????????哈希表依赖两个方法：hashCode()和equals()

????????????执行顺序：

????????????????首先判断hashCode()值是否相同

????????????????????是：继续执行equals(),看其返回值

????????????????????????是true:说明元素重复，不添加

????????????????????????是false:就直接添加到集合

????????????????????否：就直接添加到集合

????????????最终：

????????????????自动生成hashCode()和equals()即可

????????LinkedHashMap

????????????底层数据结构由链表和哈希表组成。

????????????????由链表保证元素有序。

????????????????由哈希表保证元素唯一。

????Hashtable

????????底层数据结构是哈希表。线程安全，效率低

????????????哈希表依赖两个方法：hashCode()和equals()

????????????执行顺序：

????????????????首先判断hashCode()值是否相同

????????????????????是：继续执行equals(),看其返回值

????????????????????????是true:说明元素重复，不添加

????????????????????????是false:就直接添加到集合

????????????????????否：就直接添加到集合

????????????最终：

????????????????自动生成hashCode()和equals()即可

????TreeMap

????????底层数据结构是红黑树。(是一种自平衡的二叉树)

????????????如何保证元素唯一性呢?

????????????????根据比较的返回值是否是0来决定

????????????如何保证元素的排序呢?

????????????????两种方式

????????????????????自然排序(元素具备比较性)

????????????????????????让元素所属的类实现Comparable接口

????????????????????比较器排序(集合具备比较性)

????????????????????????让集合接收一个Comparator的实现类对象

2:到底使用那种集合(自己补齐)

看需求。

是否是键值对象形式:

????是：Map

????????键是否需要排序:

????????????是：TreeMap

????????????否：HashMap

????????不知道，就使用HashMap。

????????

????否：Collection

????????元素是否唯一:

????????????是：Set

????????????????元素是否需要排序:

????????????????????是：TreeSet

????????????????????否：HashSet

????????????????不知道，就使用HashSet

????????????????

????????????否：List

????????????????要安全吗:

????????????????????是：Vector(其实我们也不用它,后面我们讲解了多线程以后，我在给你回顾用谁)

????????????????????否：ArrayList或者LinkedList

????????????????????????增删多：LinkedList

????????????????????????查询多：ArrayList

????????????????????不知道，就使用ArrayList

????????不知道，就使用ArrayList

????????

3:集合的常见方法及遍历方式

Collection:

????add()

????remove()

????contains()

????iterator()

????size()

????

????遍历：

????????增强for

????????迭代器

????????

????|--List

????????get()

????????

????????遍历：

????????????普通for

????|--Set

Map:

????put()

????remove()

????containskey(),containsValue()

????keySet()

????get()

????value()

????entrySet()

????size()

????

????遍历：

????????根据键找值

????????根据键值对对象分别找键和值

????????

作业：

????我讲解过的任意一个集合，我要求你存储什么，你就能够存储什么。

????并且，还要能够遍历出来。

4:ArrayList,LinkedList,HashSet,HashMap(掌握)

存储字符串和自定义对象数据并遍历

5:集合的嵌套遍历(理解)

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018期JavaSE面试题（十八）：JVM之垃圾回收