使用数组列表按升序和降序排列字符串

Question

我之前用一个更基本的以下代码版本编写了一篇文章。

我重新安排了它，但它仍然不起作用。每当我输入一个新的字符串，它不会进入两个列表中的任何一个。它给了我这样的：

这是你的升序排列的字符串：[]

这是你的降序排列的字符串：[]

公共类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

我会建议您使用Collections.sort();和Collections.reverse();对列表进行排序。此外，由于您已初始化descending，因此您不需要else if (descending == null)。您的代码看起来像，

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(); 
} 
} 

但是，我只会使用一个列表而不是2，因为他们都有相同的元素。像，

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(); 
} 
} 

希望它有帮助！

感谢@phflack指出排序应该在长度上&不是词法顺序。

Answer 2

你的代码几乎是正确 为了实现插入排序，你只需要与移动你的if语句出你的循环，并重置inserted变量

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); 

---

其他说明物联网您的代码：

• loop = ++loop;通常写为loop++;代替
• if(descending != null)永远不会是假的，你用它在List<String> descending = new ArrayList<>();顶部设置的东西，而不是它看起来像你的意思是写if(!descending.isEmpty())
• 写if(descending != null){ A } else if(descending == null){ B }相同(if descending != null){ A } else { B }