How to Iterate Over a Map of Maps in Java - Step by Step Examples

We can iterate over a map of maps in Java where both the outer and inner maps use integers for keys and values. This example demonstrates using nested loops to print each key-value pair.

For example,

import java.util.HashMap;
import java.util.Map;

public class IterateMapOfMaps {
    public static void main(String[] args) {
        // Declare and initialize a map of maps
        Map<Integer, Map<Integer, Integer>> outerMap = new HashMap<>();
        Map<Integer, Integer> innerMap1 = new HashMap<>();
        innerMap1.put(1, 10);
        innerMap1.put(2, 20);
        innerMap1.put(3, 30);
        outerMap.put(1, innerMap1);

        Map<Integer, Integer> innerMap2 = new HashMap<>();
        innerMap2.put(4, 40);
        innerMap2.put(5, 50);
        innerMap2.put(6, 60);
        outerMap.put(2, innerMap2);

        // Iterate over the map of maps
        System.out.println("Iterating over map of maps with integer keys and values:");
        for (Map.Entry<Integer, Map<Integer, Integer>> outerEntry : outerMap.entrySet()) {
            System.out.println("Outer key: " + outerEntry.getKey());
            for (Map.Entry<Integer, Integer> innerEntry : outerEntry.getValue().entrySet()) {
                System.out.println("  Inner key: " + innerEntry.getKey() + ", value: " + innerEntry.getValue());
            }
        }
    }
}

Iterating over map of maps with integer keys and values:
Outer key: 1
  Inner key: 1, value: 10
  Inner key: 2, value: 20
  Inner key: 3, value: 30
Outer key: 2
  Inner key: 4, value: 40
  Inner key: 5, value: 50
  Inner key: 6, value: 60

We can iterate over a map of maps in Java where the outer map uses strings for keys and the inner maps use integers for keys and strings for values. This example demonstrates using nested loops to print each key-value pair.

For example,

import java.util.HashMap;
import java.util.Map;

public class IterateMapOfMaps {
    public static void main(String[] args) {
        // Declare and initialize a map of maps
        Map<String, Map<Integer, String>> outerMap = new HashMap<>();
        Map<Integer, String> innerMap1 = new HashMap<>();
        innerMap1.put(1, "one");
        innerMap1.put(2, "two");
        innerMap1.put(3, "three");
        outerMap.put("first", innerMap1);

        Map<Integer, String> innerMap2 = new HashMap<>();
        innerMap2.put(4, "four");
        innerMap2.put(5, "five");
        innerMap2.put(6, "six");
        outerMap.put("second", innerMap2);

        // Iterate over the map of maps
        System.out.println("Iterating over map of maps with mixed key and value types:");
        for (Map.Entry<String, Map<Integer, String>> outerEntry : outerMap.entrySet()) {
            System.out.println("Outer key: " + outerEntry.getKey());
            for (Map.Entry<Integer, String> innerEntry : outerEntry.getValue().entrySet()) {
                System.out.println("  Inner key: " + innerEntry.getKey() + ", value: " + innerEntry.getValue());
            }
        }
    }
}

Iterating over map of maps with mixed key and value types:
Outer key: first
  Inner key: 1, value: one
  Inner key: 2, value: two
  Inner key: 3, value: three
Outer key: second
  Inner key: 4, value: four
  Inner key: 5, value: five
  Inner key: 6, value: six

We can iterate over a map of maps in Java where both the outer and inner maps use strings for keys and doubles for values. This example demonstrates using nested loops to print each key-value pair.

For example,

import java.util.HashMap;
import java.util.Map;

public class IterateMapOfMaps {
    public static void main(String[] args) {
        // Declare and initialize a map of maps
        Map<String, Map<String, Double>> outerMap = new HashMap<>();
        Map<String, Double> innerMap1 = new HashMap<>();
        innerMap1.put("A", 1.1);
        innerMap1.put("B", 2.2);
        innerMap1.put("C", 3.3);
        outerMap.put("group1", innerMap1);

        Map<String, Double> innerMap2 = new HashMap<>();
        innerMap2.put("D", 4.4);
        innerMap2.put("E", 5.5);
        innerMap2.put("F", 6.6);
        outerMap.put("group2", innerMap2);

        // Iterate over the map of maps
        System.out.println("Iterating over map of maps with string keys and double values:");
        for (Map.Entry<String, Map<String, Double>> outerEntry : outerMap.entrySet()) {
            System.out.println("Outer key: " + outerEntry.getKey());
            for (Map.Entry<String, Double> innerEntry : outerEntry.getValue().entrySet()) {
                System.out.println("  Inner key: " + innerEntry.getKey() + ", value: " + innerEntry.getValue());
            }
        }
    }
}

Iterating over map of maps with string keys and double values:
Outer key: group1
  Inner key: A, value: 1.1
  Inner key: B, value: 2.2
  Inner key: C, value: 3.3
Outer key: group2
  Inner key: D, value: 4.4
  Inner key: E, value: 5.5
  Inner key: F, value: 6.6