为什么番石榴中的MultiMap的size方法返回（非）预期结果？

Question

I am using MultiMap from Guava library. I created a sample MultiMap. when I print the size of map, I get 4 but the actual value (I think) should be 2. why is this discrepancy?

   import java.util.Collection;

import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.Multimap;

public class MultiMapTest {
    public static void main(String... args) {
  Multimap<String, String> myMultimap = ArrayListMultimap.create();

  // Adding some key/value
  myMultimap.put("Fruits", "Bannana");
  myMultimap.put("Fruits", "Apple");
  myMultimap.put("Fruits", "Pear");
  myMultimap.put("Vegetables", "Carrot");

  System.out.println(myMultimap);

  // Getting the size
  int size = myMultimap.size();
  System.out.println(size);  // 4

  // Getting values
  Collection<String> fruits = myMultimap.get("Fruits");
  System.out.println(fruits); // [Bannana, Apple, Pear]

  Collection<String> vegetables = myMultimap.get("Vegetables");
  System.out.println(vegetables); // [Carrot]

 }
}

Output:

Fruits=[Bannana, Apple, Pear], Vegetables=[Carrot]}
4
[Bannana, Apple, Pear]
[Carrot]

Here is the output:

From the ArrayListMultiMap docs , this should return the number of key-value pairs in the multimap. But I don't see it.

Answer 1

From Guava's API docs ,

int size()

Returns the number of key-value pairs in this multimap. Note: this method does not return the number of distinct keys in the multimap, which is given by keySet().size() or asMap().size(). See the opening section of the Multimap class documentation for clarification.

If you want to get the number of distinct keys, try

myMultimap.keySet().size()

Answer 2

size() 定义为数字键值对 ，在您的情况下为4。