Java ConcurrentHashMap putAll()用法及代碼示例

java.util.concurrent.ConcurrentHashMap.putAll()是Java中的內置函數，用於複製操作。該方法將所有元素(即映射)從一個ConcurrentHashMap複製到另一個。

用法:

new_conn_hash_map.putAll(conn_hash_map)

參數：該函數接受ConcurrentHashMap conn_hash_map作為其唯一參數，並使用此映射複製其所有映射。

返回值：該方法不返回任何值。

異常：當指定的參數為null時，該函數將引發NullPointerException。

以下示例程序旨在說明ConcurrentHashMap.putAll()方法：

示例1:該程序涉及將字符串值映射到整數鍵。

// Java Program Demonstrate putAll() 
// method of ConcurrentHashMap  
  
import java.util.concurrent.*; 
  
class ConcurrentHashMapDemo { 
    public static void main(String[] args) 
    { 
        ConcurrentHashMap<Integer, String> chm =  
                           new ConcurrentHashMap<Integer, String>(); 
        chm.put(100, "Geeks"); 
        chm.put(101, "for"); 
        chm.put(102, "Geeks"); 
        chm.put(103, "Gfg"); 
        chm.put(104, "GFG"); 
  
        // Displaying the existing HashMap 
        System.out.println("Initial Mappings are: "
                           + chm); 
  
        ConcurrentHashMap<Integer, String> new_chm =  
                            new ConcurrentHashMap<Integer, String>(); 
        new_chm.putAll(chm); 
  
        // Displaying the new map 
        System.out.println("New mappings are: "
                           + new_chm); 
    } 
}

輸出：

Initial Mappings are: {100=Geeks, 101=for, 102=Geeks, 103=Gfg, 104=GFG}
New mappings are: {100=Geeks, 101=for, 102=Geeks, 103=Gfg, 104=GFG}

示例2:該程序涉及將整數值映射到字符串鍵。

// Java Program Demonstrate putAll() 
// method of ConcurrentHashMap  
  
import java.util.concurrent.*; 
  
class ConcurrentHashMapDemo { 
    public static void main(String[] args) 
    { 
        ConcurrentHashMap<String, Integer> chm =  
                   new ConcurrentHashMap<String, Integer>(); 
        chm.put("Gfg", 100); 
        chm.put("GFG", 102); 
        chm.put("GfG", 18); 
        chm.put("gfg", 15); 
        chm.put("gfG", 55); 
  
        // Displaying the existing HashMap 
        System.out.println("Initial Mappings are: "
                           + chm); 
  
        ConcurrentHashMap<String, Integer> new_chm =  
                  new ConcurrentHashMap<String, Integer>(); 
  
        // Copying the contents 
        new_chm.putAll(chm); 
  
        // Inserting a new mapping 
        new_chm.put("gFg", 22); 
        // Displaying the new map 
        System.out.println("New mappings are: "
                           + new_chm); 
    } 
}

輸出：

Initial Mappings are: {Gfg=100, GFG=102, GfG=18, gfg=15, gfG=55}
New mappings are: {Gfg=100, GFG=102, GfG=18, gfg=15, gfG=55, gFg=22}

參考： https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ConcurrentHashMap.html#putAll()

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注：本文由純淨天空篩選整理自RICHIK BHATTACHARJEE大神的英文原創作品 ConcurrentHashMap 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。