Java sort an arraylist of objects

Question

Im trying to implement a sort method into my program following the advice from Sort an arraylist of objects in java but could not get this working. I get the error "Cannot find symbol - method sort()"

Appologies im new to java..

Entry Class:

/**
 * The Entry class represents a persons address entry into the system.
 * It holds the persons name and address information
 * 
 */
public class Entry
{
// the person's full name
private String name;
// the steet namd or number
private String street;
// the town
private String town;
// postcode
private String postcode;

/**
 * Create a new entry with a given name and address details.
 */
public Entry(String strName, String strStreet, String strTown, String strPostcode)
{
    name = strName;
    street = strStreet;
    town = strTown;
    postcode = strPostcode;
}

/**
 * Return the address for this person. The address shows the
 * street, town and postcode for the person
 * @return address
 */
public String getAddress()
{
    return name + ", " + street + ", " + town + ", " + postcode;
}

}

AddressBook class:

import java.util.*;

/**
 * The AddressBook class represents an address book holding multiple persons details. It stores
 * the name, street, town, postcode and number of entries.
 */
public class AddressBook
{
private ArrayList < Entry > entries;

/**
 * Create a an AddressBook with no limit on the number of entries
 */
public AddressBook()
{
    entries = new ArrayList < Entry >();
}

 /**
 * Return the number of address book entries
 * @return the entry amount
 */
 public String getAddressBook()
{
    String listEntries = "Address Book\n";

    listEntries = listEntries + "\nNumber of entries: " + numberOfEntries() +"\n";

    entries.sort();

    for (int i = 0; i < entries.size(); i++) {
           System.out.println(entries.get(i));
          }
    return listEntries;
}

AddressBookTextUI Class:

import java.util.*;
import java.util.regex.Matcher;
import java.util.regex.Pattern;


/**
* Provides a text based user interface for the AddressBook project.
* 
*/
public class AddressBookTextUI {
private AddressBook addressBook;
Scanner myScanner;

/**
 * Constructor for objects of class TextUI
 */
public AddressBookTextUI()
{
    addressBook = new AddressBook();
    myScanner = new Scanner(System.in);

}



private void fullCommand()
{
    System.out.println(addressBook.getAddressBook());
    clearScreen();
}

}

Answer 1

Assuming you are referring to this: entries.sort();, you would need to call Collections.sort(List<T> list) or Collection.sort(List<T> list, Comparator<T> comparator).

The difference between the two is that the first one uses a default behaviour, which can be specified in the object you will be sorting by implementing the compareTo method specified by the Comparable interface while the second allows you to pass a comparator object. This would allow you to sort the same list differently.

Answer 2

You need to use Collections.sort(List<T> list).

List is an interface. ArrayList indirect implements List interface.

Answer 3

1. Make Entry implements Comparable:

   public class Entry implements Comparable

2. Add int compareTo(Entry otherEntry) method (simplified pseudocode):

   if this > otherEntry return 1
   else if this < otherEntry return -1
   else return 0
   

3. Call Collections.sort(your array of Entries)