原因：java.lang.NullPointerException：尝试在 Android 中的空对象引用上调用虚方法 'long java.util.Date.getTime()'

Question

我想把 strSqliteDate： = 2016-01-14 05:34:50 PM 转换成 2016-01-14 。转换所有日期后，我的应用程序崩溃并收到

错误

02-01 12:03:15.204    7619-7619/com.example.tazeen.classnkk W/System.err﹕ java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference
02-01 12:03:15.204    7619-7619/com.example.tazeen.classnkk W/System.err﹕ at java.text.SimpleDateFormat.parse(SimpleDateFormat.java:1035)
02-01 12:03:15.204    7619-7619/com.example.tazeen.classnkk W/System.err﹕ at java.text.DateFormat.parse(DateFormat.java:577)

在这一行date = dateFormat.parse(strSqliteDate);

第二次在 line = calendar.setTime(date);

处出错

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'long java.util.Date.getTime()' on a null object reference at java.util.Calendar.setTime(Calendar.java:1195)

这里是DBhelper中的日期转换代码class

String strSqliteDate = cursor.getString(cursor.getColumnIndex("ActionDate"));
                Log.e(" strSqliteDate "," = " + strSqliteDate);

                String result = "";
                Date date = null;
                DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
                try
                {
                     date = dateFormat.parse(strSqliteDate);
                }
                catch(Exception e)
                {
                    e.printStackTrace();
                }
                Calendar calendar = Calendar.getInstance();
                calendar.setTime(date);
                SimpleDateFormat printFormat = new SimpleDateFormat("yyyy-MM-dd");
                result = printFormat.format(calendar.getTime());
                Log.e("result = ","==========>"+result);

Answer 1

使用subString方法参考Refers link

strSqliteDate.subString(0,10)

Output will be==>> 2016-01-14

Answer 2

在使用变量 strSqliteDate 之前检查它是否为空？

String strSqliteDate = cursor.getString(cursor.getColumnIndex("ActionDate"));
if(strSqliteDate != null && !strSqliteDate .isEmpty())
{

  Log.e(" strSqliteDate "," = " + strSqliteDate);

            String result = "";
            Date date = null;
            DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
            try
            {
                 date = dateFormat.parse(strSqliteDate);
            }
            catch(Exception e)
            {
                e.printStackTrace();
            }
            Calendar calendar = Calendar.getInstance();
            calendar.setTime(date);
            SimpleDateFormat printFormat = new SimpleDateFormat("yyyy-MM-dd");
            result = printFormat.format(calendar.getTime());
            Log.e("result = ","==========>"+result);
}

Answer 3

你的date = dateFormat.parse(strSqliteDate); strSqliteDate 是 null 这就是你得到 NPE

的原因

Answer 4

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'long java.util.Date.getTime()' on a null object reference at java.util.Calendar.setTime(Calendar.java:1195)

根据您的问题，您应该使用 substring() 并检查您的 数据库 是否 null。

This method has two variants and returns a new string that is a substring of this string. The substring begins with the character at the specified index and extends to the end of this string or up to endIndex - 1 if second argument is given.

.substring(startIndex, endIndex);

strSqliteDate = 2016-01-14 05:34:50 PM

System.out.println(strSqliteDate.substring(0, 11) );

Answer 5

第

行

result = printFormat.format(calendar.getTime());

在 formate()..

的参数中传递 Date class 的引用

原因：java.lang.NullPointerException：尝试在 Android 中的空对象引用上调用虚方法 'long java.util.Date.getTime()'

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'long java.util.Date.getTime()' on a null object reference in Android

android

datetime-format