使用数组列表按升序和降序排列字符串

Question

I wrote a post before with a much more rudimentary version of the following code.

I rearranged it, but it still doesn't work. Whenever I input a new string, it doesn't go in either of the two lists. It gives me this :

Here are your strings in ascending order : [ ]

Here are your strings in descending order : [ ]

public class Stringseries {

public static void main(String[] args) {

    Scanner scanner = new Scanner(System.in);
    System.out.println("Start the sequence by inputting a string DIFFERENT than 'quit'. When you DO want to end it, input 'quit'");
    String encore = scanner.nextLine(); 

    List<String> ascending = new ArrayList<>();
    List<String> descending = new ArrayList<>();

    int loop = 0;

    String longest = "";
    String lastInput = "";

    boolean inserted = false;

    while (!encore.equalsIgnoreCase("quit")) {

        loop = ++loop;

        encore = encore.replaceAll("\\s+",""); // this way, the length of the strings is only defined by the characters in the string, and not characters + whitespaces.

        for(int i = 0; i < ascending.size(); i++) {
            if(ascending.get(i).length() > encore.length()) {
                ascending.add(i, encore);
                inserted = true;
            } if(!inserted) { 
            ascending.add(encore); }
        } for(int i = 0; i > descending.size(); i++) {              
            if(descending.get(i).length() < encore.length()) {
                descending.add(i, encore);
                inserted = true;
            } if(!inserted) { 
            descending.add(0, encore); }
                }

        if (longest.length() < encore.length()) {
            longest = encore; }

        System.out.println("Enter the string you want to put in your sequence of strings");

        encore = scanner.nextLine();
        }

    if (descending != null) { // we check to see if the "descending" string is empty (we could do this with "ascending" mind you).
        System.out.println("Here are your strings in ascending order : " + ascending);
        System.out.println("Here are your strings in descending order : " + descending);
        System.out.println("Here is the longest string : " + longest);
    } else if (descending == null) { 
        System.out.println("You have not entered any strings, therefore the program doesn't display any string :("); // customised message.
        }
    }
}

Answer 1

I would suggest you to sort the list using Collections.sort(); and Collections.reverse(); Also, you don't need the else if (descending == null) since you already initialized descending . Your code will look something like,

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Scanner;
public class Test2 {
 public static void main(String[] args) {

  Scanner scanner = new Scanner(System.in);
  System.out.println("Start the sequence by inputting a string DIFFERENT than 'quit'. When you DO want to end it, input 'quit'");
  String longest = "";

  List<String> ascending = new ArrayList<String>();
  List<String> descending = new ArrayList<String>();
  int loop = 0;
  Comparator<String> comparator = new Comparator<String>() {
   public int compare(String o1, String o2) {
    return o1.length() - o2.length();
   }
  }


  String encore = "";
  while(true){
   loop++;
   System.out.println("Enter the string you want to put in your sequence of strings");
   encore = scanner.nextLine();
   if (encore.equalsIgnoreCase("quit")) {
    break;
   }

   encore = encore.replaceAll("\\s+", ""); // this way, the length of the strings is only defined by the characters in the string, and not characters + whitespaces

   ascending.add(encore);
   descending.add(encore);
   Collections.sort(ascending, comparator);
   Collections.sort(descending, comparator);
   Collections.reverse(descending);
  }

  for (String str: ascending) {
   if (str.length() > longest.length()) {
    longest = str;
   }
  }

  if (ascending.size() > 0) {
   System.out.println("Here are your strings in ascending order : " + ascending);
   System.out.println("Here are your strings in descending order : " + descending);
   System.out.println("Here is the longest string : " + longest);
  } else {
   System.out.println("You have not entered any strings, therefore the program doesn't display any string :("); // customised message.
  }

  scanner.close();
 }
}

However I would use only one list instead of 2, Since they both have same elements. Like,

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Scanner;

public class Test2 {
 public static void main(String[] args) {

  Scanner scanner = new Scanner(System.in);
  System.out.println("Start the sequence by inputting a string DIFFERENT than 'quit'. When you DO want to end it, input 'quit'");
  String longest = "";

  List < String > list = new ArrayList < > ();
  int loop = 0;

  String encore = "";
  while(true){
   loop++;
   System.out.println("Enter the string you want to put in your sequence of strings");
   encore = scanner.nextLine();
   encore = encore.replaceAll("\\s+", ""); // this way, the length of the strings is only defined by the characters in the string, and not characters + whitespaces

   if (encore.equalsIgnoreCase("quit")) {
    break;
   }
   list.add(encore);
  }

  for (String str: list) {
   if (str.length() > longest.length()) {
    longest = str;
   }
  }

  if (list.size() > 0) {
   Collections.sort(list, new Comparator<String>() {
    @Override
    public int compare(String o1, String o2) {
     return o1.length() - o2.length();
    }
   });
   System.out.println("Here are your strings in ascending order : " + list);
   Collections.reverse(list);
   System.out.println("Here are your strings in descending order : " + list);
   System.out.println("Here is the longest string : " + longest);
  } else {
   System.out.println("You have not entered any strings, therefore the program doesn't display any string :("); // customised message.
  }

  scanner.close();
 }
}

Hope it helps!

Thanks to @phflack for pointing out the sort should be on length & not on lexical order.

Answer 2

Your code is almost correct To implement the insertion sort, you just need to move your if statement out of your loop, and to reset your inserted variable

inserted = false;
for(int i = 0; i < ascending.size(); i++)
    if(ascending.get(i).length() > encore.length())
    {
        ascending.add(i, encore);
        inserted = true;
        break;
    }
if(!inserted)
    ascending.add(encore);

inserted = false;
for(int i = 0; i > descending.size(); i++)
    if(descending.get(i).length() < encore.length())
    {
        descending.add(i, encore);
        inserted = true;
        break;
    }
if(!inserted)
    descending.add(0, encore);

---

Other things of note with your code:

• loop = ++loop; is normally written as loop++; instead
• if(descending != null) will never be false, you're setting it to something with List<String> descending = new ArrayList<>(); at the top, instead it looks like you meant to write if(!descending.isEmpty())
• Writing if(descending != null){ A } else if(descending == null){ B } is the same as (if descending != null){ A } else { B }