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20130613

java - are "ArrayList"s of String arrays (String[]) mutable? yes

I wanted to find out if an ArrayList of String arrays (String[]) was mutable or not and i found out that it is. Here's some test code to play with:

package com.test;

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

public class ArrayMutationTest {

    public static void main(String[] args) {
        List<String[]> objList = new ArrayList<String[]>();
        String[] l1 = {"a",""};    // (K)ey, (V)alue
        String[] l2 = {"b",""};
       
        objList.add(l1);
        objList.add(l2);
       
        String csStringK = "a,b";    // (K)eys
        String csStringV = "1,2";    // (V)alues
       
        List<String> filterFieldKeys = Arrays.asList(csStringK.split("\\s*,\\s*"));
        List<String> filterFieldValues = Arrays.asList(csStringV.split("\\s*,\\s*"));

        for(Object[] ff : objList) {
            String filterKey = (String) ff[0];

            int i = filterFieldKeys.indexOf(filterKey);
            if(i != -1) {
                ff[1] = filterFieldValues.get(i);
            }
        }
    }
}


--------

after populating objList first, it looks like this:
["a", ""]
["b", ""]

after setting values in the for-loop it looks like this:
["a", "1"]
["b", "2"]

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