TreeMap putAll() Method in Java

The java.util.TreeMap.putAll() is an inbuilt method of TreeMap class that is used for the copy operation. The method copies all of the elements i.e., the mappings, from one map into another.

Syntax:

new_tree_map.putAll(exist_tree_map)

Parameters: The method takes one parameter exist_tree_map that refers to the existing map we want to copy from.

Return Value: The method does not return any values.

Exception: The method throws two types of exception:

• NullPointerException: This type of exception is thrown if the specified map is either null or it contains a null key and this map does not permit or hold null keys.
• ClassCastException: This type of exception is thrown if the specified class’ key or value is different from this map or it prevents it from being stored.

Below programs illustrates the working of java.util.TreeMap.putAll() method:
Program 1: Mapping String Values to Integer Keys.

// 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);
    }
}

Output:

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}

Program 2: Mapping Integer Values to String Keys.

// 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);
    }
}

Output:

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}

Note: The same operation can be performed with any type of Mappings with variation and combination of different data types.