map集合修改其中元素 去除Map集合中所有具有相同值的元素 Properties长久保存的流操作 两种用map记录单词或字母个数的方法

package com.swift.lianxi;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

/*1.请简述Map 的特点
2.请简述HashMap的特点
3.请简述LinkedHashMap的特点
4.使用代码依次完成：
    a).将如下键值对信息存入Map集合中:
        "黄晓明", "Baby"
        "邓超", "孙俪"
        "李晨", "范冰冰"
        "大黑牛", "范冰冰"
    b).将"李晨"对应的值替换成"白百合"
    c).获取"大黑牛"对应的值，如果是"范冰冰"就删除以"大黑牛"为键的元素

5.使用代码完成：往一个Map集合中添加若干元素.获取Map中的所有key, 并使用增强for和迭代器遍历输出每个key
6.使用代码完成：往一个Map集合中添加若干元素.获取Map集合中所有的键值对(Entry)对象, 并使用增强for和迭代器遍历输出每个key和value
7.使用代码完成：将学员的信息作为元素存入HashMap中，
    提示：1.每位学生（姓名，年龄）都有自己的家庭住址
        2.将学生对象和家庭住址存储到map集合中。学生作为键, 家庭住址作为值。
         3.学生姓名相同并且年龄相同视为同一名学生*/

public class Demo1 {

    public static void main(String[] args) {
        
        HashMap<String, String> map = new HashMap<String,String>();
        map.put("黄晓明", "Baby");
        map.put("邓超", "孙俪");
        String str1=map.put("李晨", "范冰冰");
        map.put("大黑牛", "范冰冰");
        System.out.println(map);
        //如果键值相同,直接put就是替换
        String str2=map.put("李晨", "白百合");
        System.out.println(map);
        System.out.println(str1+"..."+str2);
        String str3=map.get("大黑牛");
        if("范冰冰".equals(str3)) {
            map.remove("大黑牛");
        }
        System.out.println(map);
        
        System.out.println("===========================================");
        //keySet使用增强for遍历
        Set<String> keys = map.keySet();
        for(String key:keys) {
            System.out.println(key+"..."+map.get(key));
        }
        //keySet使用iterator遍历
        System.out.println("===========================================");
        Set<String> set =map.keySet();
        Iterator<String> it=set.iterator();
        while(it.hasNext()) {
            String name = it.next();
            System.out.println(name+"..."+map.get(name));
        }
        //entrySet使用增强for遍历
        System.out.println("===========================================");
        Set<Map.Entry<String,String>> entry = map.entrySet();
        for(Map.Entry<String, String> key:entry) {
            System.out.println(key.getKey()+"..."+key.getValue());
        }
        //entrySet使用iterator遍历
        System.out.println("===========================================");
        Set<Map.Entry<String,String>> set1 =map.entrySet();
        Iterator<Map.Entry<String,String>> it1=set1.iterator();
        while(it1.hasNext()) {
            Map.Entry<String,String> entry1= it1.next();
            System.out.println(entry1.getKey()+"..."+entry1.getValue());
        }
        
        HashMap<Student, String> students = new HashMap<Student,String>();
        students.put(new Student("zhangsan",20), "北京");
        students.put(new Student("lisi",21), "上海");
        students.put(new Student("wangwu",22), "广州");
        students.put(new Student("zhaoliu",23), "深圳");
        students.put(new Student("zhaoliu",23), "香港");
        for(Student stu:students.keySet()) {
            System.out.println(stu.toString()+"..."+students.get(stu));
        }
    }

}

class Student{
    
    private String name;
    private int age;
    private String address;
    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 String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
    public Student(String name, int age, String address) {
        super();
        this.name = name;
        this.age = age;
        this.address = address;
    }
    public Student(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }
    public Student() {
        super();
        // TODO Auto-generated constructor stub
    }
    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((address == null) ? 0 : address.hashCode());
        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 (address == null) {
            if (other.address != null)
                return false;
        } else if (!address.equals(other.address))
            return false;
        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;
    }
    @Override
    public String toString() {
        return "Student [name=" + name + ", age=" + age + ", address=" + address + "]";
    }
    
}

 去除相同值的元素

package com.swift.tuozhan;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;

/*Map中有{张三=3,李四=4,王五=5,赵六=6,孙七=7,田七=7,周八=5}这些元素.
将Map中value相同的元素从Map中去除(value为7和5是相同的,都要删除).
再将Map中剩余元素的key存放到一个ArrayLis中,并打印到控制台上*/

public class Tuozhan1 {

    public static void main(String[] args) {
        
        Map<String,Integer> map=new HashMap<String,Integer>();
        List<Integer> chongfulie = new ArrayList<Integer>();
        map.put("张三",3);
        map.put("李四",4);
        map.put("王五",5);
        map.put("赵六",6);
        map.put("孙七",7);
        map.put("田七",7);
        map.put("周八",5);
        for(String str:map.keySet()) {
            int n=map.get(str);
            chongfulie.add(n);
        }
        System.out.println(chongfulie);
        //也可以下面这样做,得到重复值
        Collection<Integer> x = map.values();
        ArrayList<Integer> a=new ArrayList<Integer>(x);
        System.out.println(a);
        //得到重复值
        List<Integer> chongfuzhi= new ArrayList<Integer>();
        for(int i=0;i<chongfulie.size();i++) {
            int zhi=chongfulie.get(i);
            for(int j=i+1;j<chongfulie.size();j++) {
                if(zhi==chongfulie.get(j)) {
                    chongfuzhi.add(zhi);
                }
            }
        }
        System.out.println(chongfuzhi);
        //得到重复键
        List<String> chongfujian= new ArrayList<String>();
        for(String str:map.keySet()) {
            Integer n1 = map.get(str);
            if(chongfuzhi.contains(n1)) {
                chongfujian.add(str);
            }
        }
        //遍历重复键,将他们都删掉
        for(String str:chongfujian) {
            map.remove(str);
        }
        System.out.println(map);
        //剩余的key 打印
        Set<String> key=map.keySet();
        ArrayList<String> arr=new ArrayList<>();
        arr.addAll(key);
        System.out.println(arr);
        
    }

}

 Properties的流操作,长久保存

package com.swift.lianxi;

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Properties;
import java.util.Set;

/*1.请简述下Properties的特点 不能放null 线程安全,速度慢
2.使用代码完成：使用Properties集合，完成把集合内容存储到IO流所对应文件中的操作
3.使用代码完成：从属性集文件prop.properties中取出数据，保存到集合中
4.简述可变参数的作用
5.使用代码完成：
    a).ArrayList集合中依次添加元素：1,2,3,4,5;
    b).使用Collections工具类将元素顺序打乱后打印所有元素
    c).使用Collections工具类将元素顺序排序后打印所有元素*/

public class Demo2 {

    public static void main(String[] args) throws FileNotFoundException, IOException {
        
        //将数据添加到Properties集合
        Properties pro = new Properties();
        pro.setProperty("zhangsan", "beijing");
        pro.setProperty("lisi", "shanghai");
        pro.setProperty("wangwu", "tianjin");
        pro.setProperty("zhaoliu", "shenzhen");
        //Properties集合内容存储到文件
        pro.store(new FileWriter("mingzhi.txt"),"a");
        
        pro.load(new FileReader("prop.properties"));
        Set<String> names = pro.stringPropertyNames();
        for(String str:names) {
            System.out.println(str+"..."+pro.getProperty(str));
        }
        
    }

}

 两种用map记录单词或字母个数的方法

package com.swift.kaoshi;

import java.util.HashMap;

//If you want to change your fate I think you must come to the dark horse to learn java 统计单词个数

public class Count {

    public static void main(String[] args) {

        String str = "If you want to change your  fate I think you must come to the dark horse to learn java ";
        str.trim();
        String[] words = str.split("\\s+");
        //两遍法,第一遍放到map中去重,第二遍放到map中计数
        for (String word : words) {

            System.out.println(word);
        }
        HashMap<String, Integer> map = new HashMap<String, Integer>();
//        for (String word : words) {
//
//            map.put(word, 0);
//        }
//        System.out.println(map);
//        for (String s : words) {
//            int num = map.get(s) + 1;
//            map.put(s, num);
//        }
//        System.out.println(map);
        //另一种方法 遍历一遍,如果值为空则放1,如果值不为空则取出加一
        for(String word:words) {
            if(map.get(word)==null) {
                map.put(word, 1);
            }else {
                map.put(word,map.get(word)+1);
            }
        }
        System.out.println(map);
    }

}