大数据必学Java基础(五十八):Map接口讲解

Map接口讲解

一、常用方法

package com.lanson.test11;

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

/**
 * @author : lanson
 */
public class Test01 {
    //这是main方法,程序的入口
    public static void main(String[] args) {
        /*
        增加:put(K key, V value)
        删除:clear() remove(Object key)
        修改:
        查看:entrySet() get(Object key) keySet() size() values()
        判断:containsKey(Object key) containsValue(Object value)
            equals(Object o) isEmpty()
         */
        //创建一个Map集合:无序,唯一
        Map<String,Integer> map = new HashMap<>();
        System.out.println(map.put("lili", 10101010));
        map.put("nana",12345234);
        map.put("feifei",34563465);
        System.out.println(map.put("lili", 34565677));
        map.put("mingming",12323);
        /*map.clear();清空*/
        /*map.remove("feifei");移除*/
        System.out.println(map.size());
        System.out.println(map);

        System.out.println(map.containsKey("lili"));
        System.out.println(map.containsValue(12323));
        Map<String,Integer> map2 = new HashMap<>();
        System.out.println(map2.put("lili", 10101010));
        map2.put("nana",12345234);
        map2.put("feifei",34563465);
        System.out.println(map2.put("lili", 34565677));
        map2.put("mingming2",12323);
        System.out.println(map==map2);
        System.out.println(map.equals(map2));//equals进行了重写,比较的是集合中的值是否一致

        System.out.println("判断是否为空:"+map.isEmpty());

        System.out.println(map.get("nana"));
        System.out.println("-----------------------------------");
        //keySet()对集合中的key进行遍历查看:
        Set<String> set = map.keySet();
        for(String s:set){
            System.out.println(s);
        }
        System.out.println("-----------------------------------");
        //values()对集合中的value进行遍历查看:
        Collection<Integer> values = map.values();
        for(Integer i:values){
            System.out.println(i);
        }
        System.out.println("-----------------------------------");
        //get(Object key) keySet()
        Set<String> set2 = map.keySet();
        for(String s:set2){
            System.out.println(map.get(s));
        }
        System.out.println("-----------------------------------");
        //entrySet()
        Set<Map.Entry<String, Integer>> entries = map.entrySet();
        for(Map.Entry<String, Integer> e:entries){
            System.out.println(e.getKey()+"----"+e.getValue());
        }
    }
}

二、TreeMap

1、key的类型为String类型

package com.lanson.test11;

import java.util.Map;
import java.util.TreeMap;

/**
 * @author : lanson
 */
public class Test02 {
    //这是main方法,程序的入口
    public static void main(String[] args) {
        Map<String,Integer> map = new TreeMap<>();
        map.put("blili",1234);
        map.put("alili",2345);
        map.put("blili",5467);
        map.put("clili",5678);
        map.put("dlili",2345);
        System.out.println(map.size());
        System.out.println(map);
    }
}

2、key的类型是一个自定义的引用数据类型

2.1、内部比较器

package com.lanson.test11;

import java.util.Map;
import java.util.TreeMap;

/**
 * @author : lanson
 */
public class Test03 {
    //这是main方法,程序的入口
    public static void main(String[] args) {
        Map<Student,Integer> map = new TreeMap<>();
        map.put(new Student(19,"blili",170.5),1001);
        map.put(new Student(18,"blili",150.5),1003);
        map.put(new Student(19,"alili",180.5),1023);
        map.put(new Student(17,"clili",140.5),1671);
        map.put(new Student(10,"dlili",160.5),1891);
        System.out.println(map);
        System.out.println(map.size());
    }
}


package com.lanson.test11;

/**
 * @author : lanson
 */
public class Student implements Comparable<Student>{
    private int age;
    private String name;
    private double height;

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getHeight() {
        return height;
    }

    public void setHeight(double height) {
        this.height = height;
    }

    public Student(int age, String name, double height) {
        this.age = age;
        this.name = name;
        this.height = height;
    }

    @Override
    public String toString() {
        return "Student{" +
                "age=" + age +
                ", name='" + name + '\\'' +
                ", height=" + height +
                '}';
    }

    @Override
    public int compareTo(Student o) {
       /* return this.getAge()-o.getAge();*/
        return this.getName().compareTo(o.getName());
    }
}

2.2、外部比较器

package com.lanson.test11;

import java.util.Comparator;
import java.util.Map;
import java.util.TreeMap;

/**
 * @author : lanson
 */
public class Test03 {
    //这是main方法,程序的入口
    public static void main(String[] args) {
        Map<Student,Integer> map = new TreeMap<>(new Comparator<Student>() {
            @Override
            public int compare(Student o1, Student o2) {
                return ((Double)(o1.getHeight())).compareTo((Double)(o2.getHeight()));
            }
        });
        map.put(new Student(19,"blili",170.5),1001);
        map.put(new Student(18,"blili",150.5),1003);
        map.put(new Student(19,"alili",180.5),1023);
        map.put(new Student(17,"clili",140.5),1671);
        map.put(new Student(10,"dlili",160.5),1891);
        System.out.println(map);
        System.out.println(map.size());
    }
}

三、Map部分整体结构图

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大数据必学Java基础(五十八):Map接口讲解
​Map接口讲解 一、常用方法 package com.lanson.test11; import java.util.Collection; import java.util.HashMap; import java.util.Map; import java.util……
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