{"id":843,"date":"2023-05-09T19:36:06","date_gmt":"2023-05-21T10:50:55","guid":{"rendered":"https:\/\/www.silicloud.com\/ja\/blog\/index.php\/2023\/11\/30\/java%e3%81%aenullpointerexception%e3%81%ae%e6%a4%9c%e5%87%ba%e3%80%81%e4%bf%ae%e6%ad%a3%e3%80%81%e3%81%8a%e3%82%88%e3%81%b3%e3%83%99%e3%82%b9%e3%83%88%e3%83%97%e3%83%a9%e3%82%af%e3%83%86%e3%82%a3\/"},"modified":"2025-08-01T02:57:21","modified_gmt":"2025-07-31T17:57:21","slug":"java%e3%81%aenullpointerexception%e3%81%ae%e6%a4%9c%e5%87%ba%e3%80%81%e4%bf%ae%e6%ad%a3%e3%80%81%e3%81%8a%e3%82%88%e3%81%b3%e3%83%99%e3%82%b9%e3%83%88%e3%83%97%e3%83%a9%e3%82%af%e3%83%86%e3%82%a3","status":"publish","type":"post","link":"https:\/\/www.silicloud.com\/ja\/blog\/java%e3%81%aenullpointerexception%e3%81%ae%e6%a4%9c%e5%87%ba%e3%80%81%e4%bf%ae%e6%ad%a3%e3%80%81%e3%81%8a%e3%82%88%e3%81%b3%e3%83%99%e3%82%b9%e3%83%88%e3%83%97%e3%83%a9%e3%82%af%e3%83%86%e3%82%a3\/","title":{"rendered":"Java\u306eNullPointerException\u306e\u691c\u51fa\u3001\u4fee\u6b63\u3001\u304a\u3088\u3073\u30d9\u30b9\u30c8\u30d7\u30e9\u30af\u30c6\u30a3\u30b9"},"content":{"rendered":"

java.lang.NullPointerException\u306f\u3001Java\u30d7\u30ed\u30b0\u30e9\u30df\u30f3\u30b0\u306b\u304a\u3044\u3066\u975e\u5e38\u306b\u4eba\u6c17\u306e\u3042\u308b\u4f8b\u5916\u306e\u4e00\u3064\u3067\u3059\u3002Java\u3067\u4f5c\u696d\u3057\u3066\u3044\u308b\u4eba\u306a\u3089\u3001Java\u306e\u30b9\u30bf\u30f3\u30c9\u30a2\u30ed\u30f3\u30d7\u30ed\u30b0\u30e9\u30e0\u3084Java\u306e\u30a6\u30a7\u30d6\u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u3067\u3044\u304d\u306a\u308a\u73fe\u308c\u308b\u3053\u3068\u3092\u76ee\u306b\u3057\u305f\u3053\u3068\u304c\u3042\u308b\u3067\u3057\u3087\u3046\u3002<\/p>\n

java.lang.NullPointerException\u3092\u65e5\u672c\u8a9e\u3067\u8a00\u3044\u63db\u3048\u308b\u3068\u3001\u6b21\u306e\u901a\u308a\u3067\u3059\uff1a\u30cc\u30eb\u30dd\u30a4\u30f3\u30bf\u4f8b\u5916<\/h2>\n
\"java<\/div>\n

NullPointerException\u306f\u30e9\u30f3\u30bf\u30a4\u30e0\u4f8b\u5916\u306a\u306e\u3067\u3001\u30d7\u30ed\u30b0\u30e9\u30e0\u5185\u3067\u30ad\u30e3\u30c3\u30c1\u3059\u308b\u5fc5\u8981\u306f\u3042\u308a\u307e\u305b\u3093\u3002NullPointerException\u306f\u3001null\u304c\u5fc5\u8981\u306a\u5834\u6240\u3067null\u306b\u5bfe\u3057\u3066\u64cd\u4f5c\u3092\u884c\u304a\u3046\u3068\u3057\u305f\u3068\u304d\u306b\u3001\u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u3067\u767a\u751f\u3057\u307e\u3059\u3002Java\u30d7\u30ed\u30b0\u30e9\u30e0\u306b\u304a\u3051\u308bNullPointerException\u306e\u4e00\u822c\u7684\u306a\u539f\u56e0\u306e\u3044\u304f\u3064\u304b\u306f\u6b21\u306e\u901a\u308a\u3067\u3059\u3002<\/p>\n

    \n
  1. \n
      \u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u30a4\u30f3\u30b9\u30bf\u30f3\u30b9\u4e0a\u306e\u30e1\u30bd\u30c3\u30c9\u3092\u547c\u3073\u51fa\u3059\u304c\u3001\u5b9f\u884c\u6642\u306b\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u304c null \u3067\u3059\u3002<\/ol>\n<\/li>\n<\/ol>\n

       <\/p>\n

        \n
      1. \n
          \u5b9f\u884c\u6642\u306b null \u3068\u306a\u3063\u3066\u3044\u308b\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u30a4\u30f3\u30b9\u30bf\u30f3\u30b9\u306e\u5909\u6570\u306b\u30a2\u30af\u30bb\u30b9\u3057\u3066\u3044\u307e\u3059\u3002<\/ol>\n<\/li>\n<\/ol>\n

           <\/p>\n

            \n
          1. \n
              \u30d7\u30ed\u30b0\u30e9\u30e0\u5185\u3067 null \u3092\u6295\u3052\u307e\u3059\u3002<\/ol>\n<\/li>\n<\/ol>\n

               <\/p>\n

                \n
              1. \n
                  null \u3068\u306a\u3063\u3066\u3044\u308b\u914d\u5217\u306e\u30a4\u30f3\u30c7\u30c3\u30af\u30b9\u306b\u30a2\u30af\u30bb\u30b9\u307e\u305f\u306f\u5024\u3092\u4fee\u6b63\u3057\u3066\u3044\u307e\u3059\u3002<\/ol>\n<\/li>\n<\/ol>\n

                   <\/p>\n

                    \u5b9f\u884c\u6642\u306b null \u3068\u306a\u3063\u3066\u3044\u308b\u914d\u5217\u306e\u9577\u3055\u3092\u30c1\u30a7\u30c3\u30af\u3057\u3066\u3044\u307e\u3059\u3002<\/ol>\n

                    Java \u306e NullPointerException \u306e\u4f8b<\/h2>\n

                    – Java \u306e NullPointerException \u306e\u4f8b
                    \n– Java \u306e NullPointerException \u306e\u30b5\u30f3\u30d7\u30eb
                    \n– Java \u306e NullPointerException \u306e\u5177\u4f53\u4f8b<\/p>\n

                    Java\u30d7\u30ed\u30b0\u30e9\u30e0\u306e\u4e2d\u3067\u3001NullPointerException\u306e\u3044\u304f\u3064\u304b\u306e\u4f8b\u3092\u898b\u3066\u307f\u307e\u3057\u3087\u3046\u3002<\/p>\n

                    1. \u30a4\u30f3\u30b9\u30bf\u30f3\u30b9\u30e1\u30bd\u30c3\u30c9\u3092\u547c\u3073\u51fa\u3059\u969b\u306eNullPointerException<\/h3>\n
                    public<\/span> class<\/span> Temp<\/span> {<\/span>\r\n\r\n\tpublic<\/span> static<\/span> void<\/span> main<\/span>(<\/span>String<\/span>[<\/span>]<\/span> args)<\/span> {<\/span>\r\n\r\n\t\tTemp<\/span> t =<\/span> initT<\/span>(<\/span>)<\/span>;<\/span>\r\n\t\t\r\n\t\tt.<\/span>foo<\/span>(<\/span>\"Hi\"<\/span>)<\/span>;<\/span>\r\n\t\t\r\n\t}<\/span>\r\n\r\n\tprivate<\/span> static<\/span> Temp<\/span> initT<\/span>(<\/span>)<\/span> {<\/span>\r\n\t\treturn<\/span> null<\/span>;<\/span>\r\n\t}<\/span>\r\n\r\n\tpublic<\/span> void<\/span> foo<\/span>(<\/span>String<\/span> s)<\/span> {<\/span>\r\n\t\tSystem<\/span>.<\/span>out.<\/span>println<\/span>(<\/span>s.<\/span>toLowerCase<\/span>(<\/span>)<\/span>)<\/span>;<\/span>\r\n\t}<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
                    \u4e0a\u8a18\u306e\u30d7\u30ed\u30b0\u30e9\u30e0\u3092\u5b9f\u884c\u3059\u308b\u3068\u3001NullPointerException\u306e\u30a8\u30e9\u30fc\u30e1\u30c3\u30bb\u30fc\u30b8\u304c\u767a\u751f\u3057\u307e\u3059\u3002<\/p>\n
                    Exception<\/span> in thread \"main\"<\/span> java.<\/span>lang.<\/span><\/span>NullPointerException<\/span>\r\n\tat Temp<\/span>.<\/span>main<\/span>(<\/span>Temp<\/span>.<\/span>java:<\/span>7<\/span>)<\/span>\r\n<\/code><\/pre>\n
                    \u300ct.foo(“Hi”);\u300d\u3068\u3044\u3046\u6587\u3067NullPointerException\u304c\u767a\u751f\u3057\u3066\u3044\u307e\u3059\u304c\u3001\u3053\u3053\u3067\u306f\u300ct\u300d\u304cnull\u3067\u3059\u3002<\/p>\n
                    2. \u30cc\u30eb\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u306e\u30d5\u30a3\u30fc\u30eb\u30c9\u306b\u30a2\u30af\u30bb\u30b9\/\u5909\u66f4\u3059\u308b\u969b\u306eJava\u306eNullPointerException<\/h3>\n
                    public<\/span> class<\/span> Temp<\/span> {<\/span>\r\n\r\n\tpublic<\/span> int<\/span> x =<\/span> 10<\/span>;<\/span>\r\n\t\r\n\tpublic<\/span> static<\/span> void<\/span> main<\/span>(<\/span>String<\/span>[<\/span>]<\/span> args)<\/span> {<\/span>\r\n\r\n\t\tTemp<\/span> t =<\/span> initT<\/span>(<\/span>)<\/span>;<\/span>\r\n\t\t\r\n\t\tint<\/span> i =<\/span> t.<\/span>x;<\/span>\r\n\t\t\r\n\t}<\/span>\r\n\r\n\tprivate<\/span> static<\/span> Temp<\/span> initT<\/span>(<\/span>)<\/span> {<\/span>\r\n\t\treturn<\/span> null<\/span>;<\/span>\r\n\t}<\/span>\r\n\r\n}<\/span>\r\n<\/code><\/pre>\n
                    \u4e0a\u8a18\u306e\u30d7\u30ed\u30b0\u30e9\u30e0\u306f\u3001\u6b21\u306eNullPointerException\u306e\u30b9\u30bf\u30c3\u30af\u30c8\u30ec\u30fc\u30b9\u3092\u6295\u3052\u307e\u3059\u3002<\/p>\n
                    Exception<\/span> in thread \"main\"<\/span> java.<\/span>lang.<\/span><\/span>NullPointerException<\/span>\r\n\tat Temp<\/span>.<\/span>main<\/span>(<\/span>Temp<\/span>.<\/span>java:<\/span>9<\/span>)<\/span>\r\n<\/code><\/pre>\n
                    \u300cNullPointerException\u300d\u306f\u3001\u300ct\u300d\u304c\u3053\u3053\u3067null\u3067\u3042\u308b\u305f\u3081\u3001\u6587\u300cint i = t.x;\u300d\u3067\u30b9\u30ed\u30fc\u3055\u308c\u307e\u3059\u3002<\/p>\n
                    3. \u30e1\u30bd\u30c3\u30c9\u306e\u5f15\u6570\u306bnull\u304c\u6e21\u3055\u308c\u305f\u5834\u5408\u306eJava\u306eNullPointerException\u3002<\/h3>\n
                    public<\/span> class<\/span> Temp<\/span> {<\/span>\r\n\r\n\tpublic<\/span> static<\/span> void<\/span> main<\/span>(<\/span>String<\/span>[<\/span>]<\/span> args)<\/span> {<\/span>\r\n\r\n\t\tfoo<\/span>(<\/span>null<\/span>)<\/span>;<\/span>\r\n\r\n\t}<\/span>\r\n\r\n\tpublic<\/span> static<\/span> void<\/span> foo<\/span>(<\/span>String<\/span> s)<\/span> {<\/span>\r\n\t\tSystem<\/span>.<\/span>out.<\/span>println<\/span>(<\/span>s.<\/span>toLowerCase<\/span>(<\/span>)<\/span>)<\/span>;<\/span>\r\n\t}<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
                    \u3053\u308c\u306f\u3001java.lang.NullPointerException\u306e\u4e2d\u3067\u3082\u6700\u3082\u4e00\u822c\u7684\u306a\u767a\u751f\u65b9\u6cd5\u306e\u4e00\u3064\u3067\u3059\u3002\u306a\u305c\u306a\u3089\u3001null\u306e\u5f15\u6570\u3092\u6e21\u3057\u3066\u3044\u308b\u306e\u306f\u547c\u3073\u51fa\u3057\u5143\u306e\u65b9\u3060\u304b\u3089\u3067\u3059\u3002<\/p>\n
                    \u4e0a\u8a18\u30d7\u30ed\u30b0\u30e9\u30e0\u304cEclipse IDE\u3067\u5b9f\u884c\u3055\u308c\u305f\u969b\u3001\u4ee5\u4e0b\u306e\u753b\u50cf\u306fnull\u30dd\u30a4\u30f3\u30bf\u30fc\u30a8\u30e9\u30fc\u3092\u793a\u3057\u3066\u3044\u307e\u3059\u3002<\/p>\n
                    \"Exception<\/div>\n
                    4. null \u304c\u6295\u3052\u3089\u308c\u305f\u5834\u5408\u306e java.lang.NullPointerException<\/h3>\n
                    public<\/span> class<\/span> Temp<\/span> {<\/span>\r\n\r\n\tpublic<\/span> static<\/span> void<\/span> main<\/span>(<\/span>String<\/span>[<\/span>]<\/span> args)<\/span> {<\/span>\r\n\r\n\t\tthrow<\/span> null<\/span>;<\/span>\r\n\t}<\/span>\r\n\r\n}<\/span>\r\n<\/code><\/pre>\n
                    \u4e0a\u8a18\u306e\u30d7\u30ed\u30b0\u30e9\u30e0\u306e\u4f8b\u5916\u30b9\u30bf\u30c3\u30af\u30c8\u30ec\u30fc\u30b9\u304c\u4ee5\u4e0b\u306b\u793a\u3055\u308c\u3066\u3044\u307e\u3059\u3002throw null; \u6587\u306e\u305f\u3081\u3001NullPointerException\u304c\u767a\u751f\u3057\u307e\u3057\u305f\u3002<\/p>\n
                    Exception<\/span> in thread \"main\"<\/span> java.<\/span>lang.<\/span><\/span>NullPointerException<\/span>\r\n\tat Temp<\/span>.<\/span>main<\/span>(<\/span>Temp<\/span>.<\/span>java:<\/span>5<\/span>)<\/span>\r\n<\/code><\/pre>\n
                    5. null\u306e\u914d\u5217\u306e\u9577\u3055\u3092\u53d6\u5f97\u3059\u308b\u969b\u306eNullPointerException<\/h3>\n
                    public<\/span> class<\/span> Temp<\/span> {<\/span>\r\n\r\n\tpublic<\/span> static<\/span> void<\/span> main<\/span>(<\/span>String<\/span>[<\/span>]<\/span> args)<\/span> {<\/span>\r\n\r\n\t\tint<\/span>[<\/span>]<\/span> data =<\/span> null<\/span>;<\/span>\r\n\t\t\r\n\t\tint<\/span> len =<\/span> data.<\/span>length;<\/span>\r\n\t}<\/span>\r\n\r\n}<\/span>\r\n<\/code><\/pre>\n
                    Exception<\/span> in thread \"main\"<\/span> java.<\/span>lang.<\/span><\/span>NullPointerException<\/span>\r\n\tat Temp<\/span>.<\/span>main<\/span>(<\/span>Temp<\/span>.<\/span>java:<\/span>7<\/span>)<\/span>\r\n<\/code><\/pre>\n
                    6. null\u306e\u914d\u5217\u306e\u30a4\u30f3\u30c7\u30c3\u30af\u30b9\u5024\u306b\u30a2\u30af\u30bb\u30b9\u3059\u308b\u3068NullPointerException\u304c\u767a\u751f\u3057\u307e\u3059\u3002<\/h3>\n
                    public<\/span> class<\/span> Temp<\/span> {<\/span>\r\n\r\n\tpublic<\/span> static<\/span> void<\/span> main<\/span>(<\/span>String<\/span>[<\/span>]<\/span> args)<\/span> {<\/span>\r\n\r\n\t\tint<\/span>[<\/span>]<\/span> data =<\/span> null<\/span>;<\/span>\r\n\t\t\r\n\t\tint<\/span> len =<\/span> data[<\/span>2<\/span>]<\/span>;<\/span>\r\n\t}<\/span>\r\n\r\n}<\/span>\r\n<\/code><\/pre>\n
                    Exception<\/span> in thread \"main\"<\/span> java.<\/span>lang.<\/span><\/span>NullPointerException<\/span>\r\n\tat Temp<\/span>.<\/span>main<\/span>(<\/span>Temp<\/span>.<\/span>java:<\/span>7<\/span>)<\/span>\r\n<\/code><\/pre>\n
                    7. null\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u4e0a\u3067\u540c\u671f\u5316\u3057\u305f\u969b\u306eNullPointerException<\/h3>\n
                    public<\/span> class<\/span> Temp<\/span> {<\/span>\r\n\r\n\tpublic<\/span> static<\/span> String<\/span> mutex =<\/span> null<\/span>;<\/span>\r\n\t\r\n\tpublic<\/span> static<\/span> void<\/span> main<\/span>(<\/span>String<\/span>[<\/span>]<\/span> args)<\/span> {<\/span>\r\n\r\n\t\tsynchronized<\/span>(<\/span>mutex)<\/span> {<\/span>\r\n\t\t\tSystem<\/span>.<\/span>out.<\/span>println<\/span>(<\/span>\"synchronized block\"<\/span>)<\/span>;<\/span>\r\n\t\t}<\/span>\t\t\r\n\t}<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
                    \u300csynchronized(mutex)\u300d\u306f\u3001\u300cmutex\u300d\u3068\u3044\u3046\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u304cnull\u3067\u3042\u308b\u305f\u3081\u3001NullPointerException\u304c\u767a\u751f\u3057\u307e\u3059\u3002<\/p>\n
                    8. HTTP \u30b9\u30c6\u30fc\u30bf\u30b9500 java.lang.NullPointerException<\/h3>\n
                    \u6642\u3005\u3001\u79c1\u305f\u3061\u306fJava\u30a6\u30a7\u30d6\u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u304b\u3089\u30a8\u30e9\u30fc\u30da\u30fc\u30b8\u306e\u5fdc\u7b54\u3092\u53d7\u3051\u53d6\u308a\u307e\u3059\u3002\u30a8\u30e9\u30fc\u30e1\u30c3\u30bb\u30fc\u30b8\u306f\u300cHTTP\u30b9\u30c6\u30fc\u30bf\u30b9500 – \u30b5\u30fc\u30d0\u30fc\u30a8\u30e9\u30fc\u300d\u3068\u306a\u308a\u3001\u539f\u56e0\u306fjava.lang.NullPointerException\u3067\u3059\u3002<\/p>\n
                    \u3053\u308c\u306b\u3064\u3044\u3066\u3001
                    \nSpring MVC\u306e\u4f8b\u306e\u30d7\u30ed\u30b8\u30a7\u30af\u30c8\u3092\u7de8\u96c6\u3057\u3001HomeController\u30e1\u30bd\u30c3\u30c9\u3092\u4ee5\u4e0b\u306e\u3088\u3046\u306b\u5909\u66f4\u3057\u307e\u3057\u305f\u3002<\/p>\n
                    @RequestMapping<\/span>(<\/span>value =<\/span> \"\/user\"<\/span>,<\/span> method =<\/span> RequestMethod<\/span>.<\/span>POST<\/span>)<\/span>\r\n\tpublic<\/span> String<\/span> user<\/span>(<\/span>@Validated<\/span> User<\/span> user,<\/span> Model<\/span> model)<\/span> {<\/span>\r\n\t\tSystem<\/span>.<\/span>out.<\/span>println<\/span>(<\/span>\"User Page Requested\"<\/span>)<\/span>;<\/span>\r\n\t\tSystem<\/span>.<\/span>out.<\/span>println<\/span>(<\/span>\"User Name: \"<\/span>+<\/span>user.<\/span>getUserName<\/span>(<\/span>)<\/span>.<\/span>toLowerCase<\/span>(<\/span>)<\/span>)<\/span>;<\/span>\r\n\t\tSystem<\/span>.<\/span>out.<\/span>println<\/span>(<\/span>\"User ID: \"<\/span>+<\/span>user.<\/span>getUserId<\/span>(<\/span>)<\/span>.<\/span>toLowerCase<\/span>(<\/span>)<\/span>)<\/span>;<\/span>\r\n\t\tmodel.<\/span>addAttribute<\/span>(<\/span>\"userName\"<\/span>,<\/span> user.<\/span>getUserName<\/span>(<\/span>)<\/span>)<\/span>;<\/span>\r\n\t\treturn<\/span> \"user\"<\/span>;<\/span>\r\n\t}<\/span>\r\n<\/code><\/pre>\n
                    \u4ee5\u4e0b\u306e\u753b\u50cf\u306f\u3001Web\u30a2\u30d7\u30ea\u30b1\u30fc\u30b7\u30e7\u30f3\u306e\u30ec\u30b9\u30dd\u30f3\u30b9\u304c\u8fd4\u3055\u308c\u305f\u969b\u306b\u8868\u793a\u3055\u308c\u308b\u30a8\u30e9\u30fc\u30e1\u30c3\u30bb\u30fc\u30b8\u3092\u793a\u3057\u3066\u3044\u307e\u3059\u3002<\/p>\n
                    \"http<\/div>\n
                    \u4ee5\u4e0b\u306f\u4f8b\u5916\u306e\u30b9\u30bf\u30c3\u30af\u30c8\u30ec\u30fc\u30b9\u3067\u3059\u3002 (Kore wa reigai no sutakku tor\u0113su desu.)<\/p>\n
                    HTTP<\/span> Status<\/span> 500<\/span> \u2013 Internal<\/span> Server<\/span> Error<\/span>\r\n\r\nType<\/span> Exception<\/span> Report<\/span>\r\n\r\nMessage<\/span> Request<\/span> processing failed;<\/span> nested exception is java.<\/span>lang.<\/span><\/span>NullPointerException<\/span>\r\n\r\nDescription<\/span> The<\/span> server encountered an unexpected condition that prevented it from fulfilling the request.<\/span><\/span>\r\n\r\nException<\/span>\r\n\r\norg.<\/span>springframework.<\/span>web.<\/span>util.<\/span><\/span>NestedServletException<\/span>:<\/span> Request<\/span> processing failed;<\/span> nested exception is java.<\/span>lang.<\/span><\/span>NullPointerException<\/span>\r\n\torg.<\/span>springframework.<\/span>web.<\/span>servlet.<\/span><\/span>FrameworkServlet<\/span>.<\/span>processRequest<\/span>(<\/span>FrameworkServlet<\/span>.<\/span>java:<\/span>982<\/span>)<\/span>\r\n\torg.<\/span>springframework.<\/span>web.<\/span>servlet.<\/span><\/span>FrameworkServlet<\/span>.<\/span>doPost<\/span>(<\/span>FrameworkServlet<\/span>.<\/span>java:<\/span>872<\/span>)<\/span>\r\n\tjavax.<\/span>servlet.<\/span>http.<\/span><\/span>HttpServlet<\/span>.<\/span>service<\/span>(<\/span>HttpServlet<\/span>.<\/span>java:<\/span>661<\/span>)<\/span>\r\n\torg.<\/span>springframework.<\/span>web.<\/span>servlet.<\/span><\/span>FrameworkServlet<\/span>.<\/span>service<\/span>(<\/span>FrameworkServlet<\/span>.<\/span>java:<\/span>846<\/span>)<\/span>\r\n\tjavax.<\/span>servlet.<\/span>http.<\/span><\/span>HttpServlet<\/span>.<\/span>service<\/span>(<\/span>HttpServlet<\/span>.<\/span>java:<\/span>742<\/span>)<\/span>\r\n\torg.<\/span>apache.<\/span>tomcat.<\/span>websocket.<\/span>server.<\/span><\/span>WsFilter<\/span>.<\/span>doFilter<\/span>(<\/span>WsFilter<\/span>.<\/span>java:<\/span>52<\/span>)<\/span>\r\nRoot<\/span> Cause<\/span>\r\n\r\njava.<\/span>lang.<\/span><\/span>NullPointerException<\/span>\r\n\tcom.<\/span>scdev.<\/span>spring.<\/span>controller.<\/span><\/span>HomeController<\/span>.<\/span>user<\/span>(<\/span>HomeController<\/span>.<\/span>java:<\/span>38<\/span>)<\/span>\r\n\tsun.<\/span>reflect.<\/span><\/span>NativeMethodAccessorImpl<\/span>.<\/span>invoke0<\/span>(<\/span>Native<\/span> Method<\/span>)<\/span>\r\n\tsun.<\/span>reflect.<\/span><\/span>NativeMethodAccessorImpl<\/span>.<\/span>invoke<\/span>(<\/span>NativeMethodAccessorImpl<\/span>.<\/span>java:<\/span>62<\/span>)<\/span>\r\n\tsun.<\/span>reflect.<\/span><\/span>DelegatingMethodAccessorImpl<\/span>.<\/span>invoke<\/span>(<\/span>DelegatingMethodAccessorImpl<\/span>.<\/span>java:<\/span>43<\/span>)<\/span>\r\n\tjava.<\/span>lang.<\/span>reflect.<\/span><\/span>Method<\/span>.<\/span>invoke<\/span>(<\/span>Method<\/span>.<\/span>java:<\/span>498<\/span>)<\/span>\r\n<\/code><\/pre>\n
                    \u30eb\u30fc\u30c8\u306e\u539f\u56e0\u306f\u3001user.getUserId().toLowerCase()\u306e\u6587\u3067\u767a\u751f\u3059\u308bNullPointerException\u3067\u3059\u3002\u306a\u305c\u306a\u3089\u3001user.getUserId()\u304cnull\u3092\u8fd4\u3057\u3066\u3044\u308b\u304b\u3089\u3067\u3059\u3002<\/p>\n
                    Java.lang.NullPointerException\u3092\u691c\u51fa\u3059\u308b\u65b9\u6cd5<\/h2>\n
                    NullPointerException\u3092\u691c\u51fa\u3059\u308b\u306e\u306f\u975e\u5e38\u306b\u7c21\u5358\u3067\u3059\u3002\u4f8b\u5916\u306e\u30c8\u30ec\u30fc\u30b9\u3092\u898b\u308c\u3070\u3001\u4f8b\u5916\u306e\u30af\u30e9\u30b9\u540d\u3068\u884c\u756a\u53f7\u304c\u8868\u793a\u3055\u308c\u307e\u3059\u3002\u305d\u3057\u3066\u3001\u30b3\u30fc\u30c9\u3092\u898b\u3066\u3001NullPointerException\u306e\u539f\u56e0\u3068\u306a\u308b\u53ef\u80fd\u6027\u304c\u3042\u308bnull\u3092\u898b\u3064\u3051\u307e\u3059\u3002\u4e0a\u8a18\u306e\u4f8b\u3092\u3059\u3079\u3066\u898b\u308c\u3070\u3001\u30b9\u30bf\u30c3\u30af\u30c8\u30ec\u30fc\u30b9\u304b\u3089\u4f55\u304cnull\u30dd\u30a4\u30f3\u30bf\u30fc\u30a8\u30af\u30bb\u30d7\u30b7\u30e7\u30f3\u306e\u539f\u56e0\u304b\u304c\u975e\u5e38\u306b\u660e\u78ba\u306b\u308f\u304b\u308a\u307e\u3059\u3002<\/p>\n
                    NullPointerException \u3092\u4fee\u6b63\u3059\u308b\u65b9\u6cd5\u306f\u4f55\u3067\u3059\u304b\u3002<\/h2>\n
                    java.lang.NullPointerException\u306f\u3001\u30c1\u30a7\u30c3\u30af\u3057\u306a\u304f\u3066\u3082\u826f\u3044\u4f8b\u5916\u3067\u3059\u306e\u3067\u3001\u79c1\u305f\u3061\u306f\u30ad\u30e3\u30c3\u30c1\u3057\u306a\u304f\u3066\u3082\u7d50\u69cb\u3067\u3059\u3002null\u30dd\u30a4\u30f3\u30bf\u30fc\u306e\u4f8b\u5916\u306f\u3001null\u306e\u30c1\u30a7\u30c3\u30af\u3068\u4e88\u9632\u7684\u306a\u30b3\u30fc\u30c7\u30a3\u30f3\u30b0\u6280\u8853\u3092\u4f7f\u3063\u3066\u9632\u3050\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002\u4ee5\u4e0b\u306e\u30b3\u30fc\u30c9\u4f8b\u3092\u898b\u3066\u3001java.lang.NullPointerException\u3092\u56de\u907f\u3059\u308b\u65b9\u6cd5\u3092\u3054\u89a7\u304f\u3060\u3055\u3044\u3002<\/p>\n
                    if<\/span>(<\/span>mutex ==<\/span>null<\/span>)<\/span> mutex =<\/span>\"\"<\/span>;<\/span> \/\/preventive coding<\/span>\r\n\t\t\r\nsynchronized<\/span>(<\/span>mutex)<\/span> {<\/span>\r\n\tSystem<\/span>.<\/span>out.<\/span>println<\/span>(<\/span>\"synchronized block\"<\/span>)<\/span>;<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
                    \/\/using null checks<\/span>\r\nif<\/span>(<\/span>user!=<\/span>null<\/span> &&<\/span> user.<\/span>getUserName<\/span>(<\/span>)<\/span> !=<\/span>null<\/span>)<\/span> {<\/span>\r\nSystem<\/span>.<\/span>out.<\/span>println<\/span>(<\/span>\"User Name: \"<\/span>+<\/span>user.<\/span>getUserName<\/span>(<\/span>)<\/span>.<\/span>toLowerCase<\/span>(<\/span>)<\/span>)<\/span>;<\/span>\r\n}<\/span>\r\nif<\/span>(<\/span>user!=<\/span>null<\/span> &&<\/span> user.<\/span>getUserName<\/span>(<\/span>)<\/span> !=<\/span>null<\/span>)<\/span> {<\/span>\r\n\tSystem<\/span>.<\/span>out.<\/span>println<\/span>(<\/span>\"User ID: \"<\/span>+<\/span>user.<\/span>getUserId<\/span>(<\/span>)<\/span>.<\/span>toLowerCase<\/span>(<\/span>)<\/span>)<\/span>;<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
                    \u30cc\u30eb\u30dd\u30a4\u30f3\u30bf\u30fc\u30a8\u30af\u30bb\u30d7\u30b7\u30e7\u30f3\u3092\u56de\u907f\u3059\u308b\u305f\u3081\u306e\u30b3\u30fc\u30c7\u30a3\u30f3\u30b0\u306e\u30d9\u30b9\u30c8\u30d7\u30e9\u30af\u30c6\u30a3\u30b9<\/h2>\n
                    \u4ee5\u4e0b\u306e\u95a2\u6570\u3092\u8003\u3048\u3001null\u30dd\u30a4\u30f3\u30bf\u30fc\u4f8b\u5916\u3092\u5f15\u304d\u8d77\u3053\u3059\u53ef\u80fd\u6027\u306e\u3042\u308b\u30b7\u30ca\u30ea\u30aa\u306b\u6ce8\u610f\u3057\u307e\u3057\u3087\u3046\u3002<\/p>\n
                    public<\/span> void<\/span> foo<\/span>(<\/span>String<\/span> s)<\/span> {<\/span>\r\n    if<\/span>(<\/span>s.<\/span>equals<\/span>(<\/span>\"Test\"<\/span>)<\/span>)<\/span> {<\/span>\r\n\tSystem<\/span>.<\/span>out.<\/span>println<\/span>(<\/span>\"test\"<\/span>)<\/span>;<\/span>\r\n    }<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
                    \u5f15\u6570\u304c null \u3068\u3057\u3066\u6e21\u3055\u308c\u308b\u5834\u5408\u3001NullPointerException \u304c\u767a\u751f\u3059\u308b\u53ef\u80fd\u6027\u304c\u3042\u308a\u307e\u3059\u3002\u540c\u3058\u30e1\u30bd\u30c3\u30c9\u306f\u3001\u4ee5\u4e0b\u306e\u3088\u3046\u306b\u66f8\u304f\u3053\u3068\u3067NullPointerException\u3092\u907f\u3051\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n
                    public<\/span> void<\/span> foo<\/span>(<\/span>String<\/span> s)<\/span> {<\/span>\r\n\tif<\/span> (<\/span>\"Test\"<\/span>.<\/span>equals<\/span>(<\/span>s)<\/span>)<\/span> {<\/span>\r\n\t\tSystem<\/span>.<\/span>out.<\/span>println<\/span>(<\/span>\"test\"<\/span>)<\/span>;<\/span>\r\n\t}<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
                    \uff12. \u5fc5\u8981\u306b\u5fdc\u3058\u3066\u3001\u5f15\u6570\u306e\u30cc\u30eb\u30c1\u30a7\u30c3\u30af\u3082\u8ffd\u52a0\u3057\u3001IllegalArgumentException \u3092\u30b9\u30ed\u30fc\u3059\u308b\u3053\u3068\u3082\u3067\u304d\u307e\u3059\u3002<\/p>\n
                    public<\/span> int<\/span> getArrayLength<\/span>(<\/span>Object<\/span>[<\/span>]<\/span> array)<\/span> {<\/span>\r\n\t\r\n\tif<\/span>(<\/span>array ==<\/span> null<\/span>)<\/span> throw<\/span> new<\/span> IllegalArgumentException<\/span>(<\/span>\"array is null\"<\/span>)<\/span>;<\/span>\r\n\t\r\n\treturn<\/span> array.<\/span>length;<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
                    3. \u4e0b\u8a18\u306e\u4f8b\u30b3\u30fc\u30c9\u306b\u793a\u3055\u308c\u3066\u3044\u308b\u3088\u3046\u306b\u3001\u4e09\u9805\u6f14\u7b97\u5b50\u3092\u4f7f\u7528\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n
                    String<\/span> msg =<\/span> (<\/span>str ==<\/span> null<\/span>)<\/span> ?<\/span> \"\"<\/span> :<\/span> str.<\/span>substring<\/span>(<\/span>0<\/span>,<\/span> str.<\/span>length<\/span>(<\/span>)<\/span>-<\/span>1<\/span>)<\/span>;<\/span>\r\n<\/code><\/pre>\n
                    \uff14. toString()\u30e1\u30bd\u30c3\u30c9\u306e\u4ee3\u308f\u308a\u306bString.valueOf()\u30e1\u30bd\u30c3\u30c9\u3092\u4f7f\u7528\u3057\u3066\u304f\u3060\u3055\u3044\u3002\u305f\u3068\u3048\u3070\u3001PrintStream\u306eprintln()\u30e1\u30bd\u30c3\u30c9\u306e\u30b3\u30fc\u30c9\u3092\u4ee5\u4e0b\u306e\u3088\u3046\u306b\u5b9a\u7fa9\u3057\u307e\u3057\u3087\u3046\u3002<\/p>\n
                    public<\/span> void<\/span> println<\/span>(<\/span>Object<\/span> x)<\/span> {<\/span>\r\n        String<\/span> s =<\/span> String<\/span>.<\/span>valueOf<\/span>(<\/span>x)<\/span>;<\/span>\r\n        synchronized<\/span> (<\/span>this<\/span>)<\/span> {<\/span>\r\n            print<\/span>(<\/span>s)<\/span>;<\/span>\r\n            newLine<\/span>(<\/span>)<\/span>;<\/span>\r\n        }<\/span>\r\n    }<\/span>\r\n<\/code><\/pre>\n
                    \u4ee5\u4e0b\u306e\u30b3\u30fc\u30c9\u30b9\u30cb\u30da\u30c3\u30c8\u306f\u3001valueOf()\u30e1\u30bd\u30c3\u30c9\u3092toString()\u306e\u4ee3\u308f\u308a\u306b\u4f7f\u7528\u3059\u308b\u4f8b\u3092\u793a\u3057\u3066\u3044\u307e\u3059\u3002<\/p>\n
                    Object<\/span> mutex =<\/span> null<\/span>;<\/span>\r\n\r\n\/\/prints null<\/span>\r\nSystem<\/span>.<\/span>out.<\/span>println<\/span>(<\/span>String<\/span>.<\/span>valueOf<\/span>(<\/span>mutex)<\/span>)<\/span>;<\/span>\r\n\r\n\/\/will throw java.lang.NullPointerException<\/span>\r\nSystem<\/span>.<\/span>out.<\/span>println<\/span>(<\/span>mutex.<\/span>toString<\/span>(<\/span>)<\/span>)<\/span>;<\/span>\r\n<\/code><\/pre>\n
                    \u3067\u304d\u308b\u9650\u308a\u3001null\u306e\u4ee3\u308f\u308a\u306b\u7a7a\u306e\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u8fd4\u3059\u30e1\u30bd\u30c3\u30c9\u3092\u66f8\u3044\u3066\u304f\u3060\u3055\u3044\u3002\u4f8b\u3048\u3070\u3001\u7a7a\u306e\u30ea\u30b9\u30c8\u3084\u7a7a\u306e\u6587\u5b57\u5217\u306a\u3069\u3067\u3059\u3002<\/p>\n
                    6. NullPointerException\u3092\u9632\u3050\u305f\u3081\u306b\u3001\u30b3\u30ec\u30af\u30b7\u30e7\u30f3\u30af\u30e9\u30b9\u306b\u306f\u3044\u304f\u3064\u304b\u306e\u30e1\u30bd\u30c3\u30c9\u304c\u5b9a\u7fa9\u3055\u308c\u3066\u3044\u307e\u3059\u306e\u3067\u3001\u305d\u308c\u3089\u3092\u4f7f\u7528\u3059\u308b\u3079\u304d\u3067\u3059\u3002\u4f8b\u3048\u3070contains()\u3001containsKey()\u3001containsValue()\u306a\u3069\u3067\u3059\u3002<\/p>\n
                    \u53c2\u7167\uff1aAPI\u30c9\u30ad\u30e5\u30e1\u30f3\u30c8<\/p>\n","protected":false},"excerpt":{"rendered":"
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