Java IdentityHashMap putAll()用法及代碼示例

java.util.IdentityHashMap.putAll()是IdentityHashMap類的內置方法，用於複製操作。該方法將所有元素，即映射，從一個映射複製到另一個。

用法:

new_Identityhash_map.putAll(exist_Identityhash_map)

參數：該方法采用一個參數exist_Identityhash_map，該參數表示我們要從中複製的現有Map。

返回值：該方法不返回任何值。

異常：如果要複製的Map為NULL，則此方法將引發NullPointerException。

以下程序說明了java.util.IdentityHashMap.putAll()方法的用法：
示例1:將字符串值映射到整數鍵。

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

輸出：

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:將整數值映射到字符串鍵。

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

輸出：

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

注意：可以對具有不同數據類型的變化和組合的任何類型的映射執行相同的操作。

相關用法

注：本文由純淨天空篩選整理自Chinmoy Lenka大神的英文原創作品 IdentityHashMap putAll() Method in Java。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。