TreeMap put() Method in Java

10 Jul, 2018
The java.util.TreeMap.put() method of TreeMap is used to insert a mapping into a map. This means we can insert a specific key and the value it is mapping to into a particular map. If an existing key is passed then the previous value gets replaced by the new value. If a new pair is passed, then the pair gets inserted as a whole.
Syntax:
Tree_Map.put(key, value)
Parameters: The method takes two parameters, both are of the Object type of the TreeMap.
key: This refers to the key element that needs to be inserted into the Map for mapping.
value: This refers to the value that the above key would map into.
Return Value: If an existing key is passed then the previous value gets returned. If a new pair is passed, then NULL is returned.
Below programs are used to illustrate the working of java.util.TreeMap.put() Method:Program 1: When passing an existing key.
// Java code to illustrate the put() methodimport 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);          // Inserting existing key along with new value        String returned_value = (String)tree_map.put(20, "All");          // Verifying the returned value        System.out.println("Returned value is: " + returned_value);          // Displayin the new map        System.out.println("New map is: " + tree_map);    }}
Initial Mappings are: {10=Geeks, 15=4, 20=Geeks, 25=Welcomes, 30=You}
Returned value is: Geeks
New map is: {10=Geeks, 15=4, 20=All, 25=Welcomes, 30=You}

Program 2: When passing a new key.
// Java code to illustrate the put() methodimport 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);          // Inserting existing key along with new value        String returned_value = (String)tree_map.put(50, "All");          // Verifying the returned value        System.out.println("Returned value is: " + returned_value);          // Displayin the new map        System.out.println("New map is: " + tree_map);    }}
Initial Mappings are: {10=Geeks, 15=4, 20=Geeks, 25=Welcomes, 30=You}
Returned value is: null
New map is: {10=Geeks, 15=4, 20=Geeks, 25=Welcomes, 30=You, 50=All}

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