How to Get Keys From HashMap in Java
Hassan Saeed
Feb 02, 2024
-
Use
keySet()to Get a Set of Keys From aHashMapin Java -
Use
keySet()to Get an Array of Keys From aHashMapin Java
This tutorial discusses methods to get the keys from a HashMap in Java.
Use keySet() to Get a Set of Keys From a HashMap in Java
The simplest way to get the keys from a HashMap in Java is to invoke the keySet() method on your HashMap object. It returns a set containing all the keys from the HashMap.
In the example below, we will first create a HashMap object, insert some values in it, and then use keySet() to get the keys.
import java.util.*;
public class MyClass {
public static void main(String args[]) {
// Create a HashMap with some values
HashMap<String, Integer> map = new HashMap<String, Integer>();
map.put("Monday", 5);
map.put("Tuesday", 6);
map.put("Wednesday", 10);
// Invoke keySet() on the HashMap object to get the keys as a set
Set<String> keys = map.keySet();
for (String key : keys) {
System.out.println(key);
}
}
}
Output:
Monday
Wednesday
Tuesday
Use keySet() to Get an Array of Keys From a HashMap in Java
Often we prefer to work with an array instead of a set. The below example illustrates how to use keySet() to get an array of keys from a HashMap in Java.
import java.util.*;
public class MyClass {
public static void main(String args[]) {
// Create a HashMap with some values
HashMap<String, Integer> map = new HashMap<String, Integer>();
map.put("Monday", 5);
map.put("Tuesday", 6);
map.put("Wednesday", 10);
// Invoke keySet() and use toArray() to get an array of keys
Object[] keys = map.keySet().toArray();
for (int i = 0; i < keys.length; i++) {
System.out.println(keys[i]);
}
}
}
Output:
Monday
Wednesday
Tuesday