Convert a Map to an Array, List and Set in Java

In this article, we will show how to convert the values of a Map to an Array, a List or a Set using Java.

1. Convert Map Values to Array

First, let’s look at converting the values of the Map into an array, using plain java:

package net.javaguides.hibernate;

import java.util.Arrays;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;

public class MapToArrayListSetExample {
    public String[] mapValuesToArray(Map < Integer, String > sourceMap) {
        Collection < String > values = sourceMap.values();
        String[] targetArray = values.toArray(new String[values.size()]);
        return targetArray;
    }

    public static void main(String[] args) {

        MapToArrayListSetExample arrayListSetExample = new MapToArrayListSetExample();
        Map < Integer, String > sourceMap = new HashMap < > ();
        sourceMap.put(100, "ABC");
        sourceMap.put(101, "PQR");
        sourceMap.put(102, "XYZ");
        String[] targetArray = arrayListSetExample.mapValuesToArray(sourceMap);
        System.out.println(Arrays.toString(targetArray));
    }
}

Output:

[ABC, PQR, XYZ]

2. Convert Map Values to List

let’s write a Java program to convert Map values to List:

package net.javaguides.hibernate;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class MapValuesToListExample {

    public List < String > mapValuesToList(Map < Integer, String > sourceMap) {
        List < String > targetList = new ArrayList < > (sourceMap.values());
        return targetList;
    }

    public static void main(String[] args) {

        MapValuesToListExample arrayListSetExample = new MapValuesToListExample();
        Map < Integer, String > sourceMap = new HashMap < > ();
        sourceMap.put(100, "ABC");
        sourceMap.put(101, "PQR");
        sourceMap.put(102, "XYZ");
        List < String > targetList = arrayListSetExample.mapValuesToList(sourceMap);
        System.out.println(targetList.toString());
    }
}

Output:

[ABC, PQR, XYZ]

3. Convert Map Values to Set

let’s write a Java program to convert Map values to Set:

package net.javaguides.hibernate;

import java.util.HashMap;

import java.util.HashSet;
import java.util.Map;
import java.util.Set;

public class MapValuesToSetExample {

    public Set < String > mapValuesToList(Map < Integer, String > sourceMap) {
        Set < String > targetList = new HashSet < > (sourceMap.values());
        return targetList;
    }

    public static void main(String[] args) {

        MapValuesToSetExample arrayListSetExample = new MapValuesToSetExample();
        Map < Integer, String > sourceMap = new HashMap < > ();
        sourceMap.put(100, "ABC");
        sourceMap.put(101, "PQR");
        sourceMap.put(102, "XYZ");
        Set < String > targetList = arrayListSetExample.mapValuesToList(sourceMap);
        System.out.println(targetList.toString());
    }
}