Java ConcurrentHashMap putAll()方法

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

语法

new_conn_hash_map.putAll(conn_hash_map)

参数： 该函数接受一个ConcurrentHashMap conn_hash_map 作为唯一的参数，并用这个map复制其所有的映射。

返回值： 该方法不返回任何值。

异常： 当指定参数为空时，该函数抛出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<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);
    }
}

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<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);
    }
}

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}

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