Java 为什么我的IF可以'；我的ArrayList&x27；s索引？

我的想法是检查ArrayList中的元素是以A、B、C开头，还是以另一个字母开头，但由于某些原因，我的IF无法获取一些单词，例如“Almofada”

---

您的问题在于for循环。在循环的每次迭代中增加索引“i”，然后删除

单词（i）处的单词。

因为我会增加，但单词列表的大小在每次迭代中都会减小，“i”会快速增加到单词列表的新大小，而不会实际计算最后的字符串

要更正，只需避免在每次迭代中增加i：

for(int i = 0; i < words.size();){ //Notice i is not being incremented (i++)
    char firstChar = words.get(i).charAt(0);
    if(firstChar == 'A'||firstChar == 'B'||firstChar == 'C'){
        abc.add(words.get(i));
    }else{
        rest.add(words.get(i));
    }
    words.remove(words.get(i));
}

for（inti=0；i

问题是因为从ArrayList中删除了单词，

单词

。删除行，

words.Remove（words.get（i））

以获得所需的输出

按如下方式操作：

import java.util.ArrayList;
import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        ArrayList<String> words = new ArrayList<>(
                Arrays.asList("Canivete", "Almofada", "Corda", "Parede", "Caixa", "Zilhão", "Dedo"));
        ArrayList abc = new ArrayList<>();
        ArrayList rest = new ArrayList<>();

        for (int i = 0; i < words.size(); i++) {
            char firstChar = words.get(i).charAt(0);
            if (firstChar == 'A' || firstChar == 'B' || firstChar == 'C') {
                abc.add(words.get(i));
            } else {
                rest.add(words.get(i));
            }
        }
        System.out.println("Start with A,B or C: " + abc);
        System.out.println("Start with other letters: " + rest);
        System.out.println("Original array: " + words);
    }
}

---

一旦从ArrayList中删除了一个元素，被删除元素右侧的所有元素都将移到一个元素的左侧。

例如，如果您有一个数组列表

A=[1,2,3,4]

并且执行

A.remove（0）

，那么结果数组列表将不是

A=[null，2,3,4]

，而是

A=[1,2,4]

程序的问题在于未能处理

remove（）

函数的这种行为

你怎么处理？ 只需更改for循环的退出条件。在您的情况下，始终检查第一个元素，并在ArrayList清空后退出，然后

words.size（）==0

。您不需要增加

i

---

解决方案

---

跳过元素是因为按位置删除元素，但这样做时不会后退。这就是为什么您应该使用

words.iterator（）

；非常感谢大家，我很感激所有的答案！！

for(int i = 0; i < words.size();){ //Notice i is not being incremented (i++)
    char firstChar = words.get(i).charAt(0);
    if(firstChar == 'A'||firstChar == 'B'||firstChar == 'C'){
        abc.add(words.get(i));
    }else{
        rest.add(words.get(i));
    }
    words.remove(words.get(i));
}

import java.util.ArrayList;
import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        ArrayList<String> words = new ArrayList<>(
                Arrays.asList("Canivete", "Almofada", "Corda", "Parede", "Caixa", "Zilhão", "Dedo"));
        ArrayList abc = new ArrayList<>();
        ArrayList rest = new ArrayList<>();

        for (int i = 0; i < words.size(); i++) {
            char firstChar = words.get(i).charAt(0);
            if (firstChar == 'A' || firstChar == 'B' || firstChar == 'C') {
                abc.add(words.get(i));
            } else {
                rest.add(words.get(i));
            }
        }
        System.out.println("Start with A,B or C: " + abc);
        System.out.println("Start with other letters: " + rest);
        System.out.println("Original array: " + words);
    }
}

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        ArrayList<String> words = new ArrayList<>(
                Arrays.asList("Canivete", "Almofada", "Corda", "Parede", "Caixa", "Zilhão", "Dedo"));
        List<String> abc = words.stream().filter(s -> s.startsWith("A") || s.startsWith("B") || s.startsWith("C"))
                .collect(Collectors.toList());
        List<String> rest = words.stream().filter(s -> !(s.startsWith("A") || s.startsWith("B") || s.startsWith("C")))
                .collect(Collectors.toList());
        System.out.println("Start with A,B or C: " + abc);
        System.out.println("Start with other letters: " + rest);
        System.out.println("Original array: " + words);
    }
}

Start with A,B or C: [Canivete, Almofada, Corda, Caixa]
Start with other letters: [Parede, Zilhão, Dedo]
Original array: [Canivete, Almofada, Corda, Parede, Caixa, Zilhão, Dedo]

public static void main(String[] args) {
    //arraylist pra verificar quais strings começam com a,b,c
    ArrayList<String> words = new ArrayList<>(
            Arrays.asList(
                    "Canivete",
                    "Almofada",
                    "Corda",
                    "Parede",
                    "Caixa",
                    "Zilhão",
                    "Dedo"
            ));

    System.out.println("Original array: " + words + "\n");

    ArrayList<String> abc = new ArrayList<>();
    ArrayList<String> rest = new ArrayList<>();

    for (int i = 0; words.size() > 0;) {
        char firstChar = words.get(i).charAt(0);
        if (firstChar == 'A' || firstChar == 'B' || firstChar == 'C') {
            abc.add(words.get(i));
        } else {
            rest.add(words.get(i));
        }
        words.remove(words.get(i));
    }
    System.out.println("Start with A,B or C: " + abc);
    System.out.println("Start with other letters: " + rest);
}

Original array: [Canivete, Almofada, Corda, Parede, Caixa, Zilhão, Dedo]

Start with A,B or C: [Canivete, Almofada, Corda, Caixa]
Start with other letters: [Parede, Zilhão, Dedo]