从方法返回时 java 列表为空

Question

I have a method that loops through a sorted Array and those sorted List elements to another list called sortedFirstName. Here is that methods code.

 public void sortFirstName(String input){
       Collections.sort(fullName, new FirstNameComparator(input)); 

       for(int i = 0;i<fullName.size();i++){
           System.out.println("\n" + fullName.get(i));
           sortedFirstName.add(fullName.get(i)); //adds to list fine

       }
        System.out.println("Sorted First Name" + sortedFirstName);
        //prints desired output, [Jake Paul, Billy Robinson, Charles Princeton, John Paul, Karen Jacobs]

FirstName is a List and is instantiated like so - List<String> fullName = new ArrayList<String>(); and is populated from a method listAllContacts like so:

public void listAllContacts(){

        for (Map.Entry<String,Person> entry : contacts.entrySet()) {
         fullName.add(entry.getValue().fullName());
}
        for (String contents : fullName) {                
           System.out.println("\n" + contents);         
      }
    }

it is populated by Strings that are a field of an object in a hashmap

from this method, I print the contents of list sortedFirstName list and get the correct output which is commented under the print statement.

I also have this get method that returns that list

public List<String> getSortedFirstNames(){
        return this.sortedFirstName;
    }

In my Junit class I am calling these methods like so

@Test
    public void sortFirst(){
        ad1.sortFirstName("Jake");
        List sorted = ad1.getSortedFirstNames();
        List sortedList = new ArrayList();
        sortedList.addAll(Arrays.asList("Jake Paul", "Billy Robinson", "Charles Princeton", "John Paul", "Karen Jacobs")); //expected output from boostrapped users
        assertEquals(sortedList,sorted);
    }

From my test case logic it should be that List sorted contains the elements [Jake Paul, Billy Robinson, Charles Princeton, John Paul, Karen Jacobs] but when I compare my hardcoded list against sorted , it shows as empty. I cannot see an issue as sortedFirstName clearly has the elements added to it, Any help would be appreciated

Answer 1

I have spotted my mistake. The listAllContacts method is needed to actually populate the fullName variable. Without the listAllContacts method being called it does not populate the fullName and in turn cannot populate the sortedFirstName list.

Here is my new code:

@Test
    public void sortFirst(){
        ad1.listAllContacts();
        ad1.sortFirstName("Jake");
        List sorted = ad1.getSortedFirstNames();
        List sortedList = new ArrayList();
        sortedList.addAll(Arrays.asList("Jake Paul", "Billy Robinson", "Charles Princeton", "John Paul", "Karen Jacobs")); //expected output from boostrapped users
        assertEquals(sortedList,sorted);
    }

note the ad1.listAllContacts(); which fixed my issue. Thanks to all who commented ti help me with this, much appreciated.