java - 如何修复索引超出范围错误？

Question

我是一名初学者java程序员，我正在尝试编写一个程序，将字符串按字母顺序排序，这段代码很困惑，但是当它消除一半字符串时，我收到了超出索引范围的错误。我确信这是由于 i 增加而 l 减少造成的，但我不确定是否有解决办法，我们将不胜感激，并且不允许我使用排序功能。

import java.util.Scanner;
import java.util.ArrayList;

public class Question6{
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        System.out.println("Please enter a string");
        String user = in.nextLine();
    int l = user.length();
    //System.out.println(l);
    int i = 0;
    System.out.println("Length is " + user.length());
    ArrayList<Character> chars = new ArrayList<Character>();
    //System.out.println(first);
    while (l > 0){
        char first = user.charAt(0);
        ArrayList<Character> earliest = new ArrayList<Character>();
        earliest.add(first);
        char char1 = user.charAt(i);
        if (char1 <= earliest.get(0)){
            earliest.remove(0);
            earliest.add(char1);
            user = user.substring(0, i) + user.substring(i+1);
            chars.add(char1);
            System.out.println("earliest in loop " + earliest.toString());
            System.out.println("chars in loop " + chars.toString());
            System.out.println("string is now " + user);
            System.out.println(" ");
            i = i+1;
            }
        else{
            chars.add(first);
            System.out.println("chars in else " + chars.toString());
            i = 0;
        }
        l = user.length();
    }

    System.out.println("done ");        
}
}

错误是

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 3
    at java.lang.String.charAt(Unknown Source)
    at Question6.main.(Question6.java:19)

这是使用字符串“Stack”作为输入

Answer 1

java.lang.String实现java.lang.Comparable ，所以你可以这样做:

if (s1.compareTo(s2) < 0) {
    //...
} else if (s1.compareTo(s2) == 0) {
    //...
} else {
    // ...
}

此外，在循环 Collection 时避免使用 remove(int)，最好使用如下的 Iterator:

Iterator<String> ite = myListString.iterator();
String str;
while(ite.hasNext()) {
     str = ite.next();
     if (/* this entry has to be removed from the list */) {
          ite.remove();
     }
}