使用 Map

一个 关于 Map 的示例

import java.util.HashMap;
import java.util.Map;
public class MapTest {
    public static void main(String[] args) {
        Map<String,Integer> scope = new HashMap<>();
        scope.put("john",100);
        scope.put("maria",59);
        for (String name : scope.keySet()){
            System.out.println(scope.get(name));
        }
    }
}

编写 equals 和 hashcode

覆写 equals

@Override
public boolean equals(Object obj) {
    if (obj instanceof Peoples){
        Peoples p = (Peoples) obj;
        return this.firstName.equals(p.firstName) && this.lastName.equals(p.lastName) && this.age == p.age;
    }
    return false;
}

覆写 hashcode

@Override
int hashCode() {
    int h = 0;
    h = 31 * h + firstName.hashCode();
    h = 31 * h + lastName.hashCode();
    h = 31 * h + age;
    return h;
}

EnumMap

import java.time.DayOfWeek;
import java.util.EnumMap;
import java.util.Map;
public class EnumMapTest {
    public static void main(String[] args) {
        Map<DayOfWeek, String> dayOfWeek = new EnumMap<>(DayOfWeek.class);
        dayOfWeek.put(DayOfWeek.MONDAY,"星期一");
        dayOfWeek.put(DayOfWeek.TUESDAY,"星期二");
        dayOfWeek.put(DayOfWeek.WEDNESDAY,"星期三");
        dayOfWeek.put(DayOfWeek.THURSDAY,"星期四");
        dayOfWeek.put(DayOfWeek.FRIDAY,"星期五");
    }
}

TreeMap

import java.util.Comparator;
import java.util.Map;
import java.util.TreeMap;
public class TreeMapTest {
    public static void main(String[] args) {
        Map<Students,Integer> s = new TreeMap<>(new Comparator<Students>() {
            @Override
            public int compare(Students s1, Students s2) {
                return s1.name.compareTo(s2.name);
            }
        });
        s.put(new Students("john"),100);
        s.put(new Students("jacob"),99);
        s.put(new Students("wewe"),34);
        s.put(new Students("dfe"),12);
        s.put(new Students("vf"),56);
        for(Students students : s.keySet()){
            System.out.println(students.name + " : "+s.get(students));
        }
    }
}
class Students{
    public String name;
    public Students(String name){
      this.name = name;
    }
}