Java 试着把一个句子分成几个单词，然后交换每个单词的第一个和最后一个字母

有人知道为什么不成功吗

以下是主类的代码：

public class FirstNLast {
    private String word[];
    private String sentence = "";
    private String newWord;
    private StringBuilder strBuff;
    private int len;
    private char firstLetter;
    private char lastLetter;

    public FirstNLast(){
        word = sentence.split(" ");
        newWord = "";
        strBuff = new StringBuilder();
        len = 0;
        firstLetter = ' ';
        lastLetter = ' ';
    }

    public void setSentence(String sentence) {
        this.sentence = sentence;
    }

    public void compute(){
        len = word.length;
        firstLetter=word[0].charAt(0);
        lastLetter=word[len-1].charAt(len-1);

        for (int i=0; i < word.length; i = i + 1) {
            if (word[i].charAt(i)==firstLetter) {
                strBuff.append(lastLetter);
            }
            else if (word[i].charAt(i)==lastLetter) {
                strBuff.append(firstLetter);
            }
            else {           
                strBuff.append(word[i].charAt(i));
            }
            newWord = strBuff.toString();
        }
    }

    public String getSentence(){
        return sentence;
    }
}

---

我的建议是使用IDE的内置调试器。设置一些断点，并使用单步执行和调试器的变量查看器来观察正在发生的情况

---

我不能给你详细的说明如何做到这一点，因为它取决于你的IDE。但毫无疑问，将有关于如何做到这一点的帮助/教程信息。在那之后，就是学习如何为自己做这件事。（你越早学会为自己做就越好！）

我没有看你的代码，但我会在标题中回答你的问题：

    String[] words = sentence.split(" ");
    String newSentence = "";

    for(String word : words){
        char[] letters = word.trim().toCharArray();
        char firstChar = letters[0];
        letters[0] = letters[letters.length - 1];
        letters[letters.length - 1] = firstChar;
        newSentence += new String(letters) + " ";
    }

    return newSentence;

---

要理解代码不起作用的原因，您应该遵循Stephen C的提示：）

以下是我为Instantiable类编写的代码。它用于交换单词的第一个字母和最后一个字母。但我的问题是我需要输入一个句子，并将其应用于句子中的每个单词，所以我离开了这个课程，创建了一个名为FirstNLast的新课程，在这个课程中我研究了如何拆分句子

public class FirstNLastWord {

    private String word;
    private String newWord;
    private StringBuffer strBuff;
    private int len;
    private char firstLetter;
    private char lastLetter;

    public FirstNLastWord() {

        word = "";
        newWord = "";
        len = 0;
        firstLetter = ' ';
        lastLetter = ' ';
    }
    public void setWord(String word) {
        this.word = word;
    }

    public void compute() {

        strBuff = new StringBuffer();
        len = word.length();
        firstLetter=word.charAt(0);
        lastLetter=word.charAt(len-1);

        for(int i=0; i < word.length(); i = i + 1) {

            if(word.charAt(i)==firstLetter) {
                strBuff.append(lastLetter);
            }
            else if(word.charAt(i)==lastLetter) {
                strBuff.append(firstLetter);
            }

            else {
                strBuff.append(word.charAt(i));

            }
            newWord = strBuff.toString();
        }
    }
    public String getNewWord() {
        return newWord;
    }
}

import javax.swing.JOptionPane;

public class FirstNLastApp{

    public static void main(String[]args){


        String sentence="";
        String word[]=sentence.split(" ");
        String newSentence="";
        StringBuffer strBuff;
        int len=0;
        char firstLetter;
        char lastLetter;

        FirstNLast fnl = new FirstNLast();


        sentence = JOptionPane.showInputDialog(null, "Please enter a sentence");


        fnl.setSentence(sentence);


        fnl.compute();

        newSentence=fnl.getNewSentence();


        JOptionPane.showMessageDialog(null, "The new sentence is " + newSentence);

    }
}

---

你能告诉我们什么不可行吗？你遇到的问题在哪里？你预计会发生什么？现在正在发生什么？这个问题看起来是从？但是这次有什么问题吗？编译很好，但没有运行。你的问题和评论就像这样说：“医生，我感觉不舒服。治疗方法是什么？”@user109649你的代码有点混乱，但这是一个很好的实践问题：）

public class FirstNLast{

    private String word[];
    private String sentence, newWord;
    private String newSentence;
    private StringBuffer strBuff;
          private int len;
    private char firstLetter;
    private char lastLetter;
    private FirstNLastWord fnl;

    public FirstNLast(){
        sentence = "";
        newSentence = "";
        strBuff = new StringBuffer();
        len = 0;
        firstLetter = ' ';
        lastLetter = ' ';
        fnl=new FirstNLastWord();
    }
    public void setSentence(String sentence){
        this.sentence = sentence;
    }
    public void compute(){

        word = sentence.split(" ");
        len = word.length;


        for(int i=0; i < word.length; i = i + 1){
            fnl.setWord(word[i]);
            fnl.compute();
            newSentence= newSentence+" "+fnl.getNewWord();
        }

     }

     public String getNewSentence(){
         return newSentence;
     }
}

import javax.swing.JOptionPane;

public class FirstNLastApp{

    public static void main(String[]args){


        String sentence="";
        String word[]=sentence.split(" ");
        String newSentence="";
        StringBuffer strBuff;
        int len=0;
        char firstLetter;
        char lastLetter;

        FirstNLast fnl = new FirstNLast();


        sentence = JOptionPane.showInputDialog(null, "Please enter a sentence");


        fnl.setSentence(sentence);


        fnl.compute();

        newSentence=fnl.getNewSentence();


        JOptionPane.showMessageDialog(null, "The new sentence is " + newSentence);

    }
}