filter strings to display three letters from the ArrayList in java

Question

I was implementing the method filter that returns a sublist of all the strings in list whose length are larger than 3. I called the filter() in the main function after I added three sample data - Hello Sam Washington. The output should be Hel Sam Was. Suggestions?

import java.util.ArrayList;

public class practice {
    private ArrayList<String> list = new ArrayList<String>();

    public ArrayList<String> filter() {
        for(int i=0; i<list.size(); i++) {
            if(list.get(i).length() > 3)
                list.set(i, list.get(i).substring(0, 3));
        }
        return list;
    }

    public static void main(String[] args) {
        ArrayList<String> list1 = new ArrayList<String>();

        list1.add("Hello");
        list1.add("Sam");
        list1.add("Washington");

        filter();

        for(int i=0; i<list1.size(); i++)
            System.out.println(list1.get(i));
    }
}

Answer 1

You are not instantiating the class Practice. You should do that and fill its list list and then call filter. I am just pasting the main method for you here.

Practice practice = new Practice();
practice.list.add("Hello");
practice.list.add("Sam");
practice.list.add("Washington");

practice.filter();

for(int i=0; i<practice.list.size(); i++)
    System.out.println(practice.list.get(i));

Answer 2

You're returning list from filter without using the returned value, or actually passing in list1. You can either add the items to list instead, or redo your method like so:

public ArrayList<String> filter(ArrayList<String> toFilter) {
    for(int i=0; i<toFilter.size(); i++) {
        if(toFilter.get(i).length() > 3)
            toFilter.set(i, toFilter.get(i).substring(0, 3));
    }
    return toFilter;
}

and then change the line filter(); to list1 = filter();, so you capture the result of the filtering.