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Java TreeMap keySet() Method with Example

TreeMap Class keySet() method: Here, we are going to learn about the keySet() method of TreeMap Class with its syntax and example.
Submitted by Preeti Jain, on February 29, 2020

TreeMap Class keySet() method

• keySet() method is available in java.util package.
• keySet() method is used to return a set of keys that exists in this TreeMap to be viewed in a Set.
• keySet() method is a non-static method, it is accessible with the class object only and if we try to access the method with the class name then we will get an error.
• keySet() method does not throw an exception at the time of returning the key set.

Syntax:

    public Set keySet();

Parameter(s):

• It does not accept any parameter.

Return value:

The return type of the method is Set, it returns contained set of keys in this TreeMap to be viewed in a Set.

Example:

// Java program to demonstrate the example 
// of Set keySet() method of TreeMap 

import java.util.*;

public class KeySetOfTreeMap {
    public static void main(String[] args) {
        // Instantiates TreeMap
        TreeMap < Integer, String > tm = new TreeMap < Integer, String > ();

        // By using put() method is
        // to put the key-value pairs in
        // treemap tm
        tm.put(1, "C");
        tm.put(4, "C++");
        tm.put(3, "Java");
        tm.put(2, "Php");

        // Display TreeMap tm
        System.out.println("tm: " + tm);

        // By using keySet() method is to
        // return the set of keys to be
        // viewed in a Set
        Set s = tm.keySet();

        // Display set view of TreeMap
        System.out.println("tm.keySet(): " + s);
    }
}

Output

tm: {1=C, 2=Php, 3=Java, 4=C++}
tm.keySet(): [1, 2, 3, 4]