Reverse HashMap keys and values in Java

Question

It\'s a simple question, I have a simple HashMap of which i want to reverse the keys and values.

HashMap myHashMap = new HashMap<         


        

Answer 1

Tested with below sample snippet, tried with MapUtils, and Java8 Stream feature. It worked with both cases.

public static void main(String[] args) {
    Map test = new HashMap();
    test.put("a", "1");
    test.put("d", "1");
    test.put("b", "2");
    test.put("c", "3");
    test.put("d", "4");
    test.put("d", "41");

    System.out.println(test);

    Map test1 = MapUtils.invertMap(test);

    System.out.println(test1);

    Map mapInversed = 
            test.entrySet()
               .stream()
               .collect(Collectors.toMap(Map.Entry::getValue, Map.Entry::getKey));

    System.out.println(mapInversed);
}

Output:
{a=1, b=2, c=3, d=41}
{1=a, 2=b, 3=c, 41=d}
{1=a, 2=b, 3=c, 41=d}