How to Print all Keys of the LinkedHashMap in Java?

Last Updated : 17 Dec, 2020

LinkedHashMap is a predefined class in Java that is similar to HashMap, contains a key and its respective value. Unlike HashMap, In LinkedHashMap insertion order is preserved. The task is to print all the Keys present in our LinkedHashMap in java. We have to iterate through each Key in our LinkedHashMap and print It.

Example :

Input : Key- 1  : Value-5      Key- 29 : Value-13      Key- 14 : Value-10      Key- 34 : Value-2      Key- 55 : Value-6    Output: 1, 29, 14, 34, 55

Method 1: Use for-each loop to iterate through LinkedHashMap. For each iteration, we print the respective key using getKey() method.

for(Map.Entry<Integer,Integer>ite : LHM.entrySet())      System.out.print(ite.getKey()+", ");

Example 1:

Java

// Java program to print all keys of the LinkedHashMap  import java.util.*; import java.io.*;  class GFG {     public static void main(String[] args)     {           // create a linkedhashmap         LinkedHashMap<Integer, Integer> LHM             = new LinkedHashMap<>();            // Add mappings         LHM.put(1, 5);         LHM.put(29, 13);         LHM.put(14, 10);         LHM.put(34, 2);         LHM.put(55, 6);            // print keys using getKey() method         for (Map.Entry<Integer, Integer> ite :              LHM.entrySet())             System.out.print(ite.getKey() + ", ");     } }

Output

1, 29, 14, 34, 55,

Example 2:

Java

// Java program to print all keys of the LinkedHashMap  import java.util.*; import java.io.*;  class GFG {     public static void main(String[] args)     {         // create a linkedhashmap         LinkedHashMap<String, String> LHM             = new LinkedHashMap<>();          // Add mappings         LHM.put("Geeks", "Geeks");         LHM.put("for", "for");         LHM.put("Geeks", "Geeks");          // print keys using getKey() method         for (Map.Entry<String, String> ite : LHM.entrySet())             System.out.print(ite.getKey() + ", ");     } }

Output

Geeks, for,

Method 2: (Using keySet() method)

Syntax:

hash_map.keySet()

Parameters: The method does not take any parameters.

Return Value: The method returns a set having the keys of the hash map.

Java

import java.io.*; import java.util.*;  class GFG {     public static void main(String[] args)     {         // create an instance of linked hashmap         LinkedHashMap<String, String> lhm             = new LinkedHashMap<String, String>();          lhm.put("One", "Geeks");         lhm.put("Two", "For");         lhm.put("Three", "Geeks");          // get all keys using the keySet method         Set<String> allKeys = lhm.keySet();          // print keys         System.out.println(allKeys);     } }