Cube Sum (HashMap)

Question: Please write a function that would print all positive numbers smaller than n that can be expressed as the sum of two cubes in two different ways. Bonus: calculate the complexity of that function.
For example, 1729 is one such number because 1729 = 1^3 + 12^3 = 9^3 + 10^3.

Idea: Binary search to find the ceiling(power(n,1/3)), then from 0 to the ceiling, we find calculate i^3+j^3, where j is from i+1 to the ceiling and store all the sum in a hashmap<sum, times appeared>. If any sum value shows up more than once, append to the result.
I would suggest not to use math.power(n, 1.0/3), since math.pow(64,1.0/3)=3.99999996.
"Output" is a class I wrote for printing my own tests, the function is just to print a list of integers if the input is not null. If the List<Integer> is null, print an "\n".

Time: O(n^2/3) Space: O(n^2/3)

Code:

 public class CubeSum {  
      public CubeSum()  
      {  
           int n1=1;  
           int n2=7;  
           int n3=8;  
           int n4=26;  
           int n5=27;  
           int n6=29;  
           int n7=1729;  
           int n8=30000;  
           Output.printList(getCubeNumbers(n1));  
           Output.printList(getCubeNumbers(n2));  
           Output.printList(getCubeNumbers(n3));  
           Output.printList(getCubeNumbers(n4));  
           Output.printList(getCubeNumbers(n5));  
           Output.printList(getCubeNumbers(n6));  
           Output.printList(getCubeNumbers(n7));  
           Output.printList(getCubeNumbers(n8));  
      }  
      public List<Integer> getCubeNumbers(int n)  
      {  
           List<Integer> result=new ArrayList<Integer>();  
           int start=0;  
           int end=cubeRootUp(n);  
           HashMap<Integer,Integer> map=new HashMap<Integer,Integer>();  
           for(int i=start;i<end;i++)  
           {  
                for(int j=i+1;j<=end;j++)  
                {  
                     int cube=i*i*i+j*j*j;  
                     if(cube<=n&&map.containsKey(cube))  
                          map.put(cube, map.get(cube)+1);  
                     else  
                          map.put(cube, 1);  
                }  
           }  
           for(int key:map.keySet())  
           {  
                if(map.get(key)>1)  
                     result.add(key);  
           }  
           return result;  
      }  
      public int cubeRootUp(int x)  
      {  
           long y=(long)x;  
           long left=0;  
           long right=x/3;  
           while(left<=right)  
           {  
                long mid=(left+right)/2;  
                long cube=mid*mid*mid;  
                if(cube==y)  
                     return (int)mid;  
                if(cube<x)  
                     left=mid+1;  
                else  
                     right=mid-1;  
           }  
           return (int)left;  
      }  
 }