Java EnumMap keySet() 方法

2024年11月8日 | 2 分钟阅读

Java EnumMap 类的 keySet() 方法用于获取映射中包含的键的集合视图。此方法以自然顺序（枚举常量声明的顺序）返回一个键集。

语法

参数

不适用

返回值

此方法返回 enum map 中包含的键的集合视图。

Exception

不适用

示例 1

import java.util.*;
public class EnumMapKeySetExample1 {
   // create an enum  
   public enum Tutorial {
   CSS, Python, PHP, Java, Javascript
   }; 
   public static void main(String[] args) {  
    //create and populate enum map  
    EnumMap<Tutorial, String >  map =
		              new EnumMap<Tutorial, String> (Tutorial.class);
    
    map.put(Tutorial.CSS, "1");
    map.put(Tutorial.Python, "2");
    map.put(Tutorial.PHP, "3");
    map.put(Tutorial.Java, "4");
    //print the map
    System.out.println("Map: "+map);
    // create a new set and return the set view of the keys contained
    Set<Tutorial>  set = map.keySet();
    // print the map again
    System.out.println("KeySet: "+set);    
   }
}

输出

Map: {CSS=1, Python=2, PHP=3, Java=4}
KeySet: [CSS, Python, PHP, Java]

示例 2

import java.util.*;
public class EnumMapKeySetExample2 {
   // create an enum  
  public enum Days {  
  Monday, Tuesday, Wednesday, Thursday  
  };  
  public static void main(String[] args) {  
  //create and populate enum map  
  EnumMap<Days, String> map= new EnumMap<Days, String>(Days.class);  
	   
  map.put(Days.Monday,"1");  
  map.put(Days.Tuesday,"2");  
  map.put(Days.Wednesday,"3");     
  //print the map
  System.out.println("Map: "+map);
  // create a new set and return the set view of the keys contained
  Set<Days>  set = map.keySet();
  // print the map again
  System.out.println("KeySet: "+set);    
  }
}

输出

Map: {Monday=1, Tuesday=2, Wednesday=3}
KeySet: [Monday, Tuesday, Wednesday]

示例 3

import java.util.*;  
public class EnumMapKeySetExample3 {   
    // create an enum  
    public enum Months {  
     January, February, March, April, May
    };  
      public static void main(String[] args) {  
      //create and populate enum map  
      EnumMap< Months, String>  map =
              new EnumMap< Months, String> (Months.class);
	   
      map.put(Months.January,"1");  
      map.put(Months.February,"2");  
      map.put(Months.March,"3");     
      map.put(Months.April,"4");      
      //print the map
      System.out.println("Map: "+map);
      // create a new set and return the set view of the keys contained
      Set<Months>  set = map.keySet();
      // print the map again
      System.out.println("KeySet: "+set);       
    }
}

输出

Map: {January=1, February=2, March=3, April=4}
KeySet: [January, February, March, April]

下一主题Java-enummap-putall-method

Java EnumMap keySet() 方法

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Exception

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示例 2

示例 3

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Java EnumMap keySet() 方法

语法

参数

返回值

Exception

示例 1

示例 2

示例 3

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