How to compare two maps by their values

Question

How to compare two maps by their values? I have two maps containing equal values and want to compare them by their values. Here is an example:

    Map a = ne         


        

Answer 1

To see if two maps have the same values, you can do the following:

• Get their Collection values() views
• Wrap into List
• Collections.sort those lists
• Test if the two lists are equals

Something like this works (though its type bounds can be improved on):

static >
boolean valuesEquals(Map map1, Map map2) {
    List values1 = new ArrayList(map1.values());
    List values2 = new ArrayList(map2.values());
    Collections.sort(values1);
    Collections.sort(values2);
    return values1.equals(values2);
}

Test harness:

Map map1 = new HashMap();
map1.put("A", "B");
map1.put("C", "D");

Map map2 = new HashMap();
map2.put("A", "D");
map2.put("C", "B");

System.out.println(valuesEquals(map1, map2)); // prints "true"

This is O(N log N) due to Collections.sort.

See also:

• Collection values()

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To test if the keys are equals is easier, because they're Set:

map1.keySet().equals(map2.keySet())

See also:

• Set keySet()