Weighted random - select random country based on population

Given a list of countries with population, how do you select random country from this list. Higher the population higher the probability of selection
https://github.com/mission-peace/interview/blob/master/src/com/interview/random/RandomCountrySelectionByPopluation.java
  public int getRandom(int []arr){
    int sum[] = new int[arr.length];
    sum[0] = arr[0];
    int n = arr[0];
    for(int i=1; i < sum.length; i++){
      sum[i] = sum[i-1] + arr[i];
      n += arr[i];
    }
   
    int ran = (int)(Math.random()*n + 1);
   
    int low = 0;
    int high = arr.length-1;
    int mid = (high + low)/2;
    while(true){
      if(sum[mid] >= ran && (mid-1 == -1 || sum[mid-1] < ran)){
        break;
      }
      if(sum[mid] > ran){
        high = mid-1;
      }else{
        low = mid+1;
      }
      mid = (high + low)/2;
    }
    return mid;
  }
https://github.com/mission-peace/interview/blob/master/src/com/interview/random/SelectMRandomNumbersInStream.java
public class SelectMRandomNumbersInStream {

  public int[] selectRandom(int arr[],int m){
    int result[] = new int[m];
    for(int i=0; i < m ;i++){
      result[i] = arr[i];
    }
   
    for(int i=m ; i < arr.length; i++){
      int random = (int)(Math.random()*i) + 1;
      if(random <= m){
        result[random-1] = arr[i];
      }
    }
    return result;
  }
}
https://github.com/mission-peace/interview/blob/master/src/com/interview/random/ShuffleArray.java
public class ShuffleArray {

  public void shuffle(int arr[]){
    for(int i=arr.length-1; i>=0; i--){
      int random = (int)(Math.random()*(i+1)) ;
      System.out.print(random +  " ");
      swap(arr,random,i);
    }
  }
 
  private void swap(int arr[],int a,int b){
    int temp = arr[a];
    arr[a] = arr[b];
    arr[b] = temp;
  }
}