我試圖找出一些 Java 基礎知識。我在下面輸入的代碼編譯得很好，但不能運行。每次運行代碼時，它都會說NullPointerException發生錯誤。class testOnStrings { public static void main (String args []){ String input, output; // isWordPalindrome input = "forever eating cheese"; boolean boolOutput = isWordPalindrome(input); System.out.println("\n" + input + (boolOutput ? " is " : " is not ") + "a word palindrome"); input = "fall leaves when leaves fall"; boolOutput = isWordPalindrome(input); System.out.println("\n" + input + (boolOutput ? " is " : " is not ") + "a word palindrome"); input = null; boolOutput = isWordPalindrome(input); System.out.println("\n" + input + (boolOutput ? " is " : " is not ") + "a word palindrome"); } static String reverseWords(String input) { // My code String words[] = input.split(" "); String reverseWord = ""; for (int pointer = words.length - 1; pointer >= 0; pointer--) reverseWord += words [pointer] + " "; return reverseWord; } static boolean isWordPalindrome(String input) { // My code String reverseWordInput = reverseWords(input); boolean isPalindrome = input.equals(reverseWordInput); return isPalindrome; }}運行代碼時出現錯誤。Exception in thread "main" java.lang.NullPointerException at idle.reverseWords(idle.java:21) at idle.isWordPalindrome(idle.java:30) at idle.main(idle.java:15)請幫忙，因為編譯成功但代碼沒有運行
2 回答
交互式愛情
TA貢獻1712條經驗 獲得超3個贊
我建議在方法中處理特殊/角落情況，而不是期望調用者以空或null字符串行事。
您可以增強isWordPalindrome處理null,zero或singlecharacter 的方法，以便可以處理任何類型的輸入。
發件人
static boolean isWordPalindrome(String input) {
// My code
String reverseWordInput = reverseWords(input);
boolean isPalindrome = input.equals(reverseWordInput);
return isPalindrome;
}
至
static boolean isWordPalindrome(String input) {
// My code
if (input == null || input.length() == 0 || input.length() == 1) return true;
String reverseWordInput = reverseWords(input);
boolean isPalindrome = input.equals(reverseWordInput);
return isPalindrome;
}
上面的增強也將避免調用reverseWords的null，zero或single性格。
同樣，我也會增強reverseWords。
發件人
static String reverseWords(String input) {
// My code
String words[] = input.split(" ");
String reverseWord = "";
for (int pointer = words.length - 1; pointer >= 0; pointer--)
reverseWord += words [pointer] + " ";
return reverseWord;
}
至
static String reverseWords(String input) {
// My code
if (input == null || input.length() == 0 || input.length() == 1) return input;
String words[] = input.split(" ");
String reverseWord = "";
for (int pointer = words.length - 1; pointer >= 0; pointer--)
reverseWord += words [pointer] + " ";
return reverseWord;
}
慕桂英4014372
TA貢獻1871條經驗 獲得超13個贊
您已將問題指定input為 null
input = null; boolOutput = isWordPalindrome(input);
為輸入分配空字符串值以防您不想要任何東西
input = ""; boolOutput = isWordPalindrome(input);
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