Java中的 ConcurrentHashMap putAll() 方法

Java .util.concurrent.ConcurrentHashMap.putAll()是Java中的一个内置函数，用于复制操作。该方法将所有元素（即映射）从一个 ConcurrentHashMap 复制到另一个。

句法：

new_conn_hash_map.putAll(conn_hash_map)

参数：该函数接受 ConcurrentHashMap conn_hash_map作为其唯一参数，并使用此映射复制其所有映射。

返回值：该方法不返回任何值。

异常：当指定参数为null时，函数抛出NullPointerException。

下面的程序说明了 ConcurrentHashMap.putAll() 方法：

程序 1：该程序涉及将字符串值映射到整数键。

// Java Program Demonstrate putAll()
// method of ConcurrentHashMap 
  
import java.util.concurrent.*;
  
class ConcurrentHashMapDemo {
    public static void main(String[] args)
    {
        ConcurrentHashMap chm = 
                           new ConcurrentHashMap();
        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 new_chm = 
                            new ConcurrentHashMap();
        new_chm.putAll(chm);
  
        // Displaying the new map
        System.out.println("New mappings are: "
                           + new_chm);
    }
}

输出：

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}

程序 2：该程序涉及将整数值映射到字符串键。

// Java Program Demonstrate putAll()
// method of ConcurrentHashMap 
  
import java.util.concurrent.*;
  
class ConcurrentHashMapDemo {
    public static void main(String[] args)
    {
        ConcurrentHashMap chm = 
                   new ConcurrentHashMap();
        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 new_chm = 
                  new ConcurrentHashMap();
  
        // 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);
    }
}

输出：

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}

参考：https: Java/util/concurrent/ConcurrentHashMap.html#putAll()