Java WeakHashMap putall()用法及代码示例

java.util.WeakHashMap.putAll()是WeakHashMap类的内置方法，用于复制操作。该方法将所有元素，即映射，从一个映射复制到另一个。

用法:

new_weakhash_map.putAll(exist_weakhash_map)

参数：该方法采用一个参数exist_weakhash_map，该参数表示我们要从中复制的现有Map。

返回值：该方法不返回任何值。

异常：如果要复制的Map为NULL，则此方法将引发NullPointerException。

以下示例程序旨在说明java.util.WeakHashMap.putAll()方法的用法：
示例1:将字符串值映射到整数键。

// Java code to illustrate the putAll() method 
import java.util.*; 
  
public class Weak_Hash_Map_Demo { 
    public static void main(String[] args) 
    { 
  
        // Creating an empty WeakHashMap 
        Map<Integer, String> weak_hash = new 
                      WeakHashMap<Integer, String>(); 
  
        // Mapping string values to int keys 
        weak_hash.put(10, "Geeks"); 
        weak_hash.put(15, "4"); 
        weak_hash.put(20, "Geeks"); 
        weak_hash.put(25, "Welcomes"); 
        weak_hash.put(30, "You"); 
  
        // Displaying the WeakHashMap 
        System.out.println("Initial Mappings are: " +  
                                           weak_hash); 
  
        // Creating a new weakhash map and copying 
        Map<Integer, String> new_weakhash_map = new 
                        WeakHashMap<Integer, String>(); 
        new_weakhash_map.putAll(weak_hash); 
  
        // Displaying the final WeakHashMap 
        System.out.println("The new map: " +  
                                    new_weakhash_map); 
    } 
}

输出：

Initial Mappings are: {30=You, 15=4, 10=Geeks, 25=Welcomes, 20=Geeks}
The new map: {15=4, 30=You, 10=Geeks, 25=Welcomes, 20=Geeks}

示例2:将整数值映射到字符串键。

// Java code to illustrate the putAll() method 
import java.util.*; 
  
public class WeakHash_Map_Demo { 
    public static void main(String[] args) 
    { 
  
        // Creating an empty WeakHashMap 
        Map<String, Integer> weak_hash = new 
                      WeakHashMap<String, Integer>(); 
  
        // Mapping int values to string keys 
        weak_hash.put("Geeks", 10); 
        weak_hash.put("4", 15); 
        weak_hash.put("Geeks", 20); 
        weak_hash.put("Welcomes", 25); 
        weak_hash.put("You", 30); 
  
        // Displaying the WeakHashMap 
        System.out.println("Initial Mappings are: " +  
                                          weak_hash); 
  
        // Creating a new weakhash map and copying 
        Map<String, Integer> new_weakhash_map = new 
                      WeakHashMap<String, Integer>(); 
        new_weakhash_map.putAll(weak_hash); 
  
        // Displaying the final WeakHashMap 
        System.out.println("The new map: " +  
                                   new_weakhash_map); 
    } 
}

输出：

Initial Mappings are: {Welcomes=25, 4=15, You=30, Geeks=20}
The new map: {Welcomes=25, 4=15, You=30, Geeks=20}

注意：可以对具有不同数据类型的变化和组合的任何类型的映射执行相同的操作。

相关用法

注：本文由纯净天空筛选整理自Chinmoy Lenka大神的英文原创作品 WeakHashMap putall() Method in Java。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。