Java - 如何计算出现频率？

Question

The method printearthquakes() is going to list each country for which there was one or more earthquakes as well as the number of earthquakes detected in that country.

I have two different lists one of which contains the name of all countries and the other one keeps record of earthquake information ie location, magnitude, etc. The expected outcome should look something like this

Nepal: 1
United States of America: 9
Uzbekistan: 1 

My program loops over the list of countries as well as earthquakes to find out if any country has happened to have one or more earthquakes and it attempts to print the name of that country and the number of earthquakes occurred there.

private void printearthquakes() 
{

    int numOfQuakes = 0;

    if (quakeMarkers.size()>0)
    {
      for (Marker country: countryMarkers)
       {
        boolean firstpass = false;
        for(Marker quake : quakeMarkers)
        {

            if ( country.getProperty("name").equals(quake.getProperty("country")))
            {
                numOfQuakes++;
                System.out.println(country.getProperty("name"));
                System.out.println(numOfQuakes);

            }   
        }           
    }       
  }
}

All it does is repeating the country names for as many times as they appear in the earthquake list and counting from 0 :

Nepal
1
United States of America
2
United States of America
3
United States of America
4
United States of America
5
United States of America
6
United States of America
7
United States of America
8
United States of America
9
United States of America
10
Uzbekistan
11

I'd like to know where I am getting this wrong and how to fix it!

Answer 1

you need to re-initialize counter for each country and display result only once per country, like this:

private void printearthquakes() {
    for (Marker country: countryMarkers) {
        int numOfQuakes = 0;
        for(Marker quake : quakeMarkers)
            if (country.getProperty("name").equals(quake.getProperty("country")))
                numOfQuakes++;
        System.out.println(country.getProperty("name"));
        System.out.println(numOfQuakes);
    }
}

NOTE: this is O(n^2) version, to speed-up process I'd suggest another approach:

private void printearthquakes() {
    Map<String, Long> quakes = new HashMap<>();
    for(Marker quake : quakeMarkers) {
        Long cnt = quakes.get(quake.getProperty("country"));
        quakes.put(quake.getProperty("country"), (cnt!=null?cnt.longValue():0) + 1L);
    }
    for (Entry<String, Long> e: quakes.entrySet()) {
        System.out.println(e.getKey());
        System.out.println(e.getValue());
    }
}

which is O(n) only