比较两个 HashMap 并乘以 map 值

Question

I have two HashMap and lets say they having the following values:

 HashMap1 : <x, 1>, <y, 2>, <z, 3>

 HashMap2 : <x,10>, <y, 20>, <z,30>

I want to multiply corresponding values then sum these values like: 1*10 + 2*20 + 3*30. However, I am not sure if I have to use 2 loops or some other iteration. I use one loop but it did no solved the problem:

for (Map.Entry<Character, Integer> entry : map1.entrySet()) {
    int sum=0;
    if(map2.containsKey(entry.getKey())) {
        sum+=entry.getValue() * ...; //it gets map1 values but I also need map2 values to multiply
    }
}

How to fix it?

Answer 1

Before Java 8 :

int sum = 0;
for (Map.Entry<String, Integer> entry : map1.entrySet()) {
    sum += entry.getValue() * map2.getOrDefault(entry.getKey(), 1);
}

Since Java 8 :

int sum = map1.entrySet().stream()
   .mapToInt(e -> e.getValue() * map2.getOrDefault(e.getKey(), 1)).sum();

Note:
You need to also handle keys which are different between two maps. I assumed that these two maps contains exactly the same keys. Just to keep it simple and clear.