Java EnumMap put() 方法

Java java.util.EnumMap.put(key,value) 方法用于将指定的键值对关联起来。如果键已存在，旧的值会被替换。

语法

Enum_Map.put(key, value)

使用的参数：
该方法接受两个参数：

• key – 与值关联的指定键
• value – 与指定键关联的值

返回值：
返回与指定键关联的旧值（如果之前没有映射，则返回 null）。

下面的程序说明了 put(key,value) 方法的工作方式：

程序1：

// Java program to demonstrate keySet()
import java.util.*;
  
// An enum of geeksforgeeks
public enum gfg {
    Global_today,
    India_today,
    China
}
;
  
class Enum_demo {
    public static void main(String[] args)
    {
  
        EnumMap<gfg, Integer> mp = new 
                 EnumMap<gfg, Integer>(gfg.class);
  
        // Values are associated
        mp.put(gfg.Global_today, 799);
        mp.put(gfg.India_today, 69);
  
       // Display the initial map
       System.out.println("The map is: " + mp);
  
        // Stores the old value associated with the key
        int prev_value = mp.put(gfg.India_today, 72);
  
        // Prints the old value
        System.out.println("Previous value: " + prev_value);
  
       // Display the final map
       System.out.println("The final map is: " + mp);
    }
}

输出：

The map is: {Global_today=799, India_today=69}
Previous value: 69
The final map is: {Global_today=799, India_today=72}

程序2

// Java program to demonstrate the working of keySet()
import java.util.*;
  
// an enum of geeksforgeeks
// ranking globally and in india
public enum gfg {
    Global_today,
    India_today,
    China_today
}
;
  
class Enum_demo {
    public static void main(String[] args)
    {
  
        EnumMap<gfg, Integer> mp = new EnumMap<gfg, Integer>(gfg.class);
  
        // Values are associated
        mp.put(gfg.Global_today, 799);
        mp.put(gfg.India_today, 69);
  
       // Display the initial map
       System.out.println("The map is: " + mp);
  
        // Stores the old value associated with the key
        int prev_value = mp.put(gfg.Global_today, 800);
  
        // Prints the old value
        System.out.println("Previous value: " + prev_value);
  
       // Display the final map
       System.out.println("The final map is: " + mp);
    }
}

输出：

The map is: {Global_today=799, India_today=69}
Previous value: 799
The final map is: {Global_today=800, India_today=69}