大数据必学Java基础（五十八）：Map接口讲解
【摘要】 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...
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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