Need help mapping this data in Java

I am having problems mapping this data

          1           35
          1           30
          1           20
          2           10
       开发者_JAVA百科   3           40
          3           25
          3           15

I tried using the HashMap but it would only map to the last occurrence of this data.

The behavior of Map and HashMap you describe is the intended behavior, as other commenters note. What you want is a multimap. You can roll your own (don't do this-- other commenters suggest maps to lists, but that quickly becomes cumbersome. If you really want to roll your own, roll your own generic multimap with list/set values and hide the complexity.) or use Guava's multimap. Example:

import com.google.common.collect.HashMultimap;
import com.google.common.collect.SetMultimap;

  public static void main(String[] args) 
  {
    final SetMultimap<Integer, Integer> foo = HashMultimap.create();
    foo.put( 1,35);
    foo.put(   1,30);
    foo.put(  1,20);
    foo.put(  2,10);
    foo.put(  3,40);
    foo.put(  3,25);
    foo.put(  3,15);
    System.out.println(foo);
  }

Output:

{1=[35, 20, 30], 2=[10], 3=[25, 40, 15]}

If you want to access the values, there are a couple of ways depending on what you want to do. Just calling get(Integer key) will return a collection of the values.

Also, check out this answer, which cites lots of related goodness in Guava.

The documentation states:

public interface Map
An object that maps keys to values. A map cannot contain duplicate keys; each key can map to at most one value.

Instead, you can associate a list of numbers with each key.

You could use Map<Long, List<Long>> (or whatever type you have) to address this problem.

A Map only has single value for a key. You can use the Multimap interface from Guava / Google Collections to store multiple values for a key.

Or create a Pair< F, S > class and put them in a list

List< Pair< Integer, Integer > >