引起: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

我想将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得到错误

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)

在这条线上 date = dateFormat.parse(strSqliteDate);

第二个得到错误 line = calendar.setTime(date);

引发者:java.lang.NullPointerException:尝试在java.util.Calendar.setTime(Calendar.java:1195)的空对象引用上调用虚方法'long java.util.Date.getTime()'

这是DBhelper类中的日期转换代码

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

在使用变量strSqliteDate之前检查它是否为null？

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);
}