Sort circles into rows and columns in Java

I am developing an android app with opencv and I have convert c++ code to java about finded hough circles in java. I find c++ code and convert limited.

this lines find and fill lists :

vector<vector<Vec3f> > bubble;  
vector<pair<double,int> > row;  
for(int i=0;i<circles.size();i++){  
    bool found = false;  
    int r = cvRound(circles[i][2]);   
    int x = cvRound(circles[i][0]);  
    int y= cvRound(circles[i][1]);  
    for(int j=0;j<row.size();j++){  
        int y2 = row[j].first;  
        if(y-r<y2&&y+r>y2){  
            bubble[j].push_back(circles[i]);  
            found = true;  
            break;  
        }  
    }  

    if(!found){  
        int l = row.size();  
        row.push_back(make_pair(y,l));  
        vector<Vec3f> v;  
        v.push_back(circles[i]);  
        bubble.push_back(v);  
   } 

   found = false;  
}  

this lines sort the lists:

bool comparator2(pair<double,int> a,pair<double,int> b){  
    retu a.first<b.first;  
}  

bool comparator3(Vec3f a,Vec3f b){  
    retu a[0]<b[0];  
}  

sort(row.begin(),row.end(),comparator2);  
for(int i=0;i<bubble.size();i++){  
    sort(bubble[i].begin(),bubble[i].end(),comparator3);  
}