java.util.TreeMap.putAll()是TreeMap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映射。

句法:

new_tree_map.putAll(exist_tree_map)

参数:该方法采用一个参数exist_tree_map,该参数引用我们要复制的现有map。

返回值:该方法不返回任何值。

异常:该方法抛出两种类型的异常:

  • NullPointerException:如果指定的映射为null或包含null键且此映射不允许或保留null键,则抛出此类型的异常。
  • ClassCastException:如果指定的类的键或值与此映射不同或者它阻止存储它,则抛出此类型的异常。

下面的程序说明了java.util.TreeMap.putAll()方法的工作原理

程序1:将字符串值映射到整数键。

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

输出:

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

程序2:将整数值映射到字符串键。

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

输出:

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

注意:对于具有不同数据类型的变体和组合的任何类型的映射,都可以执行相同的操作。

 
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