iterate hashmap in java and best way to iterate hashmap in java

Q: Can we iterate a HashMap directly in Java?

No. A HashMap stores data as key-value entries, so you cannot traverse the map object directly the way you can with a HashSet. You iterate it indirectly through its keys, its values, or its entries.

Q: Which method should I use to iterate a HashMap?

It depends on the scenario: use keySet() when you need each value based on its key, use values() when you only care about the values and not any order, and use entrySet() when you need the key and the value at the same time.

Q: What is the difference between using iterator() and forEach() to iterate a HashMap?

Both approaches cover the same three sources (keys, values, and entries). The iterator() method returns an Iterator that you drive with hasNext() and next(), while the forEach() loop lets you iterate over keySet(), values(), or entrySet() directly.

Q: Which HashMap methods are used to iterate over a map?

The examples rely on the keySet() method, the values() method, and the entrySet() method, together with the iterator() method and the forEach() loop.

Q: Does iterating a HashMap guarantee any order?

If you only want the values and you don't care about any order, you can iterate using values(). If ordering matters for your use case, refer to the related HashMap topics linked from this page.

Like other collections, we can’t directly traverse map in java. To iterate hashmap in java we can use the HashMap iterator() method and java map foreach() method. In this post, we will see how to Iterate a HashMap in Java.

As we already know HashMap stores data in form of entry and each entry is a pair of keys and value. But we can’t directly iterate the objects of HashMap, unlike HashSet. Here we have some methods that are used to get the objects from HashMap. Before moving further we should know about the keySet() method, values() method, and entrySet() method.

iterate map in java

We can iterate a hashmap in java by use of its keys, values, and entries. Now it will depend on the scenario which method you should use:

1. If you want to get each value based on the key then you should iterate based on keys(By keySet())
2. If you just want to use values of HashMap and you don’t care about any order then use-values. (By values)
3. If you want to key and values at the same time then use entire(By entrySet())

By use of the iterator() method iterate through hashmap

Let’s see the example, Here we will see how we can iterator by use of keySet() method.

import java.util.HashMap;
import java.util.Iterator;
public class HashMapExample
{
   public static void main(String args[])
   {
	   HashMap<Integer, String> hashMap = new HashMap<Integer, String>();
	   hashMap.put(1, "JavaGoal.com");
	   hashMap.put(2, "Learning");
	   hashMap.put(3, "Website");
	   Iterator<Integer> hashMapKey = hashMap.keySet().iterator();
	   while(hashMapKey.hasNext())
	   {
		   Integer key = hashMapKey.next();
		   System.out.println("Key: "+ key);
		   System.out.println("Value from Key: "+ hashMap.get(key));
	   }
   }
}

Output: Key: 1
Value from Key: JavaGoal.com
Key: 2
Value from Key: Learning
Key: 3
Value from Key: Website

Let’s see the another example, Here we will see how we can iterator by use of values() method.

import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
public class HashMapExample
{
   public static void main(String args[])
   {
	   HashMap<Integer, String> hashMap = new HashMap<Integer, String>();
	   hashMap.put(1, "JavaGoal.com");
	   hashMap.put(2, "Learning");
	   hashMap.put(3, "Website");
	   Collection<String> hashMapValues = hashMap.values();
	   Iterator<String> values = hashMapValues.iterator();
	   while(values.hasNext())
	   {
		   System.out.println("Value from HashMap: "+ values.next());
	   }
   }
}

Output:Value from HashMap: JavaGoal.com
Value from HashMap: Learning
Value from HashMap: Website

Let’s see the another example, Here we will see how we can iterator by use of entrySet() method.

import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map.Entry;
public class HashMapExample
{
   public static void main(String args[])
   {
	   HashMap<Integer, String> hashMap = new HashMap<Integer, String>();
	   hashMap.put(1, "JavaGoal.com");
	   hashMap.put(2, "Learning");
	   hashMap.put(3, "Website");
	   Collection<Entry<Integer, String>> allEntrySet = hashMap.entrySet();
	   Iterator<Entry<Integer, String>> entriesIterator = allEntrySet.iterator();
	   while(entriesIterator.hasNext())
	   {
		   System.out.println("Entry from HashMap: "+entriesIterator.next());
	   }
   }
}

Output: Entry from HashMap: 1=JavaGoal.com
Entry from HashMap: 2=Learning
Entry from HashMap: 3=Website

Java map foreach

We can transverse a HashMap in java by the use of java hashmap foreach() method. Here we will discuss the same ways to iterate the HashMap by forEach() method.

import java.util.HashMap;
public class HashMapExample
{
   public static void main(String args[])
   {
	   HashMap<Integer, String> hashMap = new HashMap<Integer, String>();
	   hashMap.put(1, "JavaGoal.com");
	   hashMap.put(2, "Learning");
	   hashMap.put(3, "Website");
	   for(Integer key : hashMap.keySet())
	   {
		   System.out.println("Key: "+ key);
		   System.out.println("Value from Key: "+ hashMap.get(key));
	   }
   }
}

Output: Key: 1
Value from Key: JavaGoal.com
Key: 2
Value from Key: Learning
Key: 3
Value from Key: Website

import java.util.HashMap;
public class HashMapExample
{
   public static void main(String args[])
   {
	   HashMap<Integer, String> hashMap = new HashMap<Integer, String>();
	   hashMap.put(1, "JavaGoal.com");
	   hashMap.put(2, "Learning");
	   hashMap.put(3, "Website");
	   for(String value : hashMap.values())
	   {
		   System.out.println("Value from HashMap: "+ value);
	   }
   }
}

Output: Value from HashMap: JavaGoal.com
Value from HashMap: Learning
Value from HashMap: Website

import java.util.HashMap;
import java.util.Map.Entry;
public class HashMapExample
{
   public static void main(String args[])
   {
	   HashMap<Integer, String> hashMap = new HashMap<Integer, String>();
	   hashMap.put(1, "JavaGoal.com");
	   hashMap.put(2, "Learning");
	   hashMap.put(3, "Website");
	   for(Entry<Integer, String> entry : hashMap.entrySet())
	   {
		   System.out.println("Key and Value from HashMap: "+ entry);
	   }
   }
}

Output: Key and Value from HashMap: 1=JavaGoal.com
Key and Value from HashMap: 2=Learning
Key and Value from HashMap: 3=Website

Frequently asked questions

Can we iterate a HashMap directly in Java?

No. As explained above, a HashMap stores data as key-value entries, so you cannot traverse the map object directly the way you can with a HashSet. You iterate it indirectly through its keys, its values, or its entries.

Which method should I use to iterate a HashMap?

It depends on the scenario: use keySet() when you need each value based on its key, use values() when you only care about the values and not any order, and use entrySet() when you need the key and the value at the same time.

What is the difference between using iterator() and forEach() to iterate a HashMap?

Both approaches are shown in this post and cover the same three sources (keys, values, and entries). The iterator() method returns an Iterator that you drive with hasNext() and next(), while the forEach() loop lets you iterate over keySet(), values(), or entrySet() directly.

Which HashMap methods are used to iterate over a map?

The examples in this post rely on the keySet() method, the values() method, and the entrySet() method, together with the iterator() method and the forEach() loop.

Does iterating a HashMap guarantee any order?

The post notes that if you only want the values and you don't care about any order, you can iterate using values(). If ordering matters for your use case, refer to the related HashMap topics linked from this page.

How to iterate hashmap in java