NULL指针异常故障

Question

所以我正在制作PigLatin Converter，我有一些NullPointerException。现在你可能会问我是否尝试过自己去改变我的答案是，是的，我尝试过。无论如何，这是我的代码:导致错误的行将以"ERROR"结束

package project.pkg16.pkg9;
public class Project169_Data {
private static String[] words;
private static String pigLatinWords;
public static void setWords( String input ) {
    words = input.split(" ");
}
public static String convertToPigLatin() {
    for (int i = 0; i < words.length; i++) {
        String wordTemp = null;
        String word = words[i].toString();
            char firstLetter = word.charAt(0);
            StringBuilder sb = new StringBuilder(word.toString());
            sb.append( String.valueOf(firstLetter).toLowerCase() );
            sb.deleteCharAt(0);
            sb.append("ay ");
            StringBuilder sb2 = new StringBuilder(wordTemp);   LINE 24 ERROR
            sb2.append(sb.toString());
            pigLatinWords = sb2.toString();
            }
       return pigLatinWords;
    }
}

然后是第二类:

package project.pkg16.pkg9;
public class Project169_Main {
public static Project169_Input project169_Input = new Project169_Input();
public static Project169_Data project169_Data = new Project169_Data();
public static void main(String[] args) {
    String userInput = Project169_Input.getInput();
    project169_Data.setWords(userInput);
    String pigLatinString = project169_Data.convertToPigLatin();       LINE 14 ERROR
 }
}

最后是第三类:

package project.pkg16.pkg9;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
public class Project169_Input {
public static String getInput() {
JFrame frame = new JFrame("English to Pig Latin");
String input = JOptionPane.showInputDialog(frame, "Enter the english words you wish to convert to Pig Latin.");
return input;
} //End of method...
} //End of Class...

错误是:

运行:

    Exception in thread "main" java.lang.NullPointerException
at java.lang.StringBuilder.<init>(StringBuilder.java:92)
at project.pkg16.pkg9.Project169_Data.convertToPigLatin(Project169_Data.java:24)
at project.pkg16.pkg9.Project169_Main.main(Project169_Main.java:14)
    BUILD SUCCESSFUL (total time: 31 seconds)

Answer 1

wordTemp为空且永不更改。您正在尝试创建一个带有null变量的StringBuilder。

解决方法:不要这样做。

作为题外话:下次，请通过注释指出哪一行抛出了NPE。您还没有这样做仍然，即使在编辑之后。请不要强迫我们一次只计算一行代码。比如:

StringBuilder sb2 = new StringBuilder(wordTemp);  // **** this line throws NPE
sb2.append(sb.toString());
pigLatinWords = sb2.toString();

,

• 你会想要修复你的代码格式，特别是当前的缩进错误，使你和我们难以调试。
• 我认为你真的想创建没有参数的StringBuilder，并且在 for循环之前。
• 我认为你想在 for循环之后调用StringBuilder 上的toString()。