ArrayList 不添加元素

Question

My array list is supposed to have a line of asterisk before and after each occurrence of the smallest number in it. I have debugged and all variables are holding the correct values but for some reason it wont add the values.

Here is my code:

int smallest = array[0];

        for (int i = 0; i < size; i++) 
            if (array[i] < smallest) 
                smallest = array[i];

                String smallestString = String.valueOf(smallest);

        ArrayList<String> list = new ArrayList<String>();

        for(int i = 0;i < size; i++)
            list.add(Integer.toString(array[i]));


        for (int i = 0; i < list.size(); i++)
        if (smallestString.equals(list.get(i))) {
            list.add(i, "*****"); 
            list.add(i + 2, "*****");
        }

            System.out.println("\n" + list);

            return smallest;

Answer 1

I think it is better to construct list as you go. Your way of inserting a new element to list (which is an ArrayList implementation) has two problems:

1. The library is forced to shift everything by one -- this is slow
2. In general changing a list while iterating it is error prone.

I would rewrite the code as follows:

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class ArrayListInsert {

    public static void main(String[] args) {
        Integer[] array = new Integer[]{1, 5, 2, 6, 7};

        int smallest = array[0];

        for (int i = 0; i < array.length; i++) 
            if (array[i] < smallest) 
                smallest = array[i];

        String smallestString = String.valueOf(smallest);

        List<String> list = new ArrayList<String>();

        for(int i = 0; i < array.length; i++) {
            if (smallestString.equals(String.valueOf(array[i]))) { // be careful!
                list.add("*****"); 
                list.add(Integer.toString(array[i]));
                list.add("*****");
            } else {
                list.add(Integer.toString(array[i]));
            }
        }

        System.out.println("array is\n" + Arrays.deepToString(array));
        System.out.println("list is\n" + list);

//            return smallest;

    }

}

The output would be:

array is 
[1, 5, 2, 6, 7]
list is
[*****, 1, *****, 5, 2, 6, 7]