How To Iterate Map In Java?

There are multiple ways to iterate over a Map In Java which we will learn with examples in this post.

Using entrySet() Method

The Map interface has a method called entrySet() which returns a collection view of the map as Map.Entry. Entry is an inner interface of the Map interface.

Set> entries = mapData.entrySet();
for (Map.Entry keyValue: entries) {
  String key = keyValue.getKey();
  String value = keyValue.getValue();
  System.out.println("Key = " + key + " | Value = " + value);
}

Using keySet() method

We can retrieve all keys at once using the keySet() method in a Set and then iterate it over to get the associated value.

Set allKeys = mapData.keySet();
for (String key: allKeys) {
  String value = mapData.get(key);
  System.out.println("Key = " + key + " | Value = " + value);
}

Using values() method

Unlike keySet() method, we can extract all values at once using the values() method. But we can not backtrack their associated keys. So using this method we can get both keys and values together.

Collection allValues = mapData.values();
for (String value: allValues) {
  System.out.println("Value = " + value);
}

Using iterator() method

We can use the iterator() method that provides an iterator over a collection. The Iterator interface takes the place of the Enumeration interface in the Java Collections Framework. You can use this instead of the ‘for’ loop. You can call the iterator() method in the output of all three methods above.

Iterator allKeysUsingIterator = mapData.keySet().iterator();
while (allKeysUsingIterator.hasNext()) {
  String key = allKeysUsingIterator.next();
  String value = mapData.get(key);
  System.out.println("Key = " + key + " | Value = " + value);
}

Complete Program

package collectionsExamples;

import java.util.*;

public class IterateMap {

    public static void main(String[] args) {
        //create a map data
        HashMap mapData = new HashMap<>();
        mapData.put("id","1");
        mapData.put("name","Amod");
        mapData.put("address","New York");
        mapData.put("skills","Java Selenium");
        mapData.put("mob","969768");

        // Iterate using entrySet() method
        Set> entries = mapData.entrySet();
        for(Map.Entry keyValue : entries) {
            String key = keyValue.getKey();
            String value = keyValue.getValue();
            System.out.println("Key = " + key + " | Value = " + value);
        }

        // Iterate using keySet() method
        Set allKeys = mapData.keySet();
        for(String key : allKeys) {
            String value = mapData.get(key);
            System.out.println("Key = " + key + " | Value = " + value);
        }

        // Iterate using values() method
        Collection allValues = mapData.values();
        for(String value : allValues) {
            System.out.println("Value = " + value);
        }

        // Iterate using iterate() method
        Iterator allKeysUsingIterator = mapData.keySet().iterator();
        while(allKeysUsingIterator.hasNext()) {
            String key = allKeysUsingIterator.next();
            String value = mapData.get(key);
            System.out.println("Key = " + key + " | Value = " + value);
        }
    }
}

Output

For all ways except the values() method, the output will be as below. For the values() method way we will just get values, not keys.

Key = skills | Value = Java Selenium
Key = mob | Value = 969768
Key = address | Value = New York
Key = name | Value = Amod
Key = id | Value = 1

We can also use lambda function and Stream concepts which I will cover in the next post.

Thanks for reading.

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