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📜 Java EnumMap类
📅 最后修改于: 2020-10-13 00:33:06 🧑 作者: Mango
Java EnumMap类
Java EnumMap类是枚举键的专用Map实现。它继承了Enum和AbstractMap类。
EnumMap类层次结构
EnumMap类的层次结构在下图中给出。
EnumMap类声明
我们来看一下java.util.EnumMap类的声明。
public class EnumMap,V> extends AbstractMap implements Serializable, Cloneable
EnumMap类参数
让我们看一下java.util.EnumMap类的参数。
- K：这是此地图维护的键的类型。
- V：这是映射值的类型。
Java EnumMap类的构造方法
| Constructor | Description |
|---|---|
| EnumMap(Class |
It is used to create an empty enum map with the specified key type. |
| EnumMap(EnumMap |
It is used to create an enum map with the same key type as the specified enum map. |
| EnumMap(Map |
It is used to create an enum map initialized from the specified map. |
Java EnumMap类的方法
| SN | Method | Description |
|---|---|---|
| 1 | clear() | It is used to clear all the mapping from the map. |
| 2 | clone() | It is used to copy the mapped value of one map to another map. |
| 3 | containsKey() | It is used to check whether a specified key is present in this map or not. |
| 4 | containsValue() | It is used to check whether one or more key is associated with a given value or not. |
| 5 | entrySet() | It is used to create a set of elements contained in the EnumMap. |
| 6 | equals() | It is used to compare two maps for equality. |
| 7 | get() | It is used to get the mapped value of the specified key. |
| 8 | hashCode() | It is used to get the hashcode value of the EnumMap. |
| 9 | keySet() | It is used to get the set view of the keys contained in the map. |
| 10 | size() | It is used to get the size of the EnumMap. |
| 11 | Values() | It is used to create a collection view of the values contained in this map. |
| 12 | put() | It is used to associate the given value with the given key in this EnumMap. |
| 13 | putAll() | It is used to copy all the mappings from one EnumMap to a new EnumMap. |
| 14 | remove() | It is used to remove the mapping for the given key from EnumMap if the given key is present. |
Java EnumMap示例
import java.util.*;
public class EnumMapExample {
// create an enum
public enum Days {
Monday, Tuesday, Wednesday, Thursday
};
public static void main(String[] args) {
//create and populate enum map
EnumMap map = new EnumMap(Days.class);
map.put(Days.Monday, "1");
map.put(Days.Tuesday, "2");
map.put(Days.Wednesday, "3");
map.put(Days.Thursday, "4");
// print the map
for(Map.Entry m:map.entrySet()){
System.out.println(m.getKey()+" "+m.getValue());
}
}
}
输出：
Monday 1
Tuesday 2
Wednesday 3
Thursday 4
Java EnumMap示例：书籍
import java.util.*;
class Book {
int id;
String name,author,publisher;
int quantity;
public Book(int id, String name, String author, String publisher, int quantity) {
this.id = id;
this.name = name;
this.author = author;
this.publisher = publisher;
this.quantity = quantity;
}
}
public class EnumMapExample {
// Creating enum
public enum Key{
One, Two, Three
};
public static void main(String[] args) {
EnumMap map = new EnumMap(Key.class);
// Creating Books
Book b1=new Book(101,"Let us C","Yashwant Kanetkar","BPB",8);
Book b2=new Book(102,"Data Communications & Networking","Forouzan","Mc Graw Hill",4);
Book b3=new Book(103,"Operating System","Galvin","Wiley",6);
// Adding Books to Map
map.put(Key.One, b1);
map.put(Key.Two, b2);
map.put(Key.Three, b3);
// Traversing EnumMap
for(Map.Entry entry:map.entrySet()){
Book b=entry.getValue();
System.out.println(b.id+" "+b.name+" "+b.author+" "+b.publisher+" "+b.quantity);
}
}
}
输出：
101 Let us C Yashwant Kanetkar BPB 8
102 Data Communications & Networking Forouzan Mc Graw Hill 4
103 Operating System Galvin Wiley 6