java.lang.NullPointerException Main.java:6 [duplicate]

Question

I have two classes

I am not sure why this is erroring. In eclipse there are no red underlines.

Main:

package com.example; public class Main { public static void main(String[] args) { Week myWeek = new Week(Week.days.FRIDAY); System.out.println(myWeek.Today.toString()); } }

Week:

package com.example; public class Week { public static enum days { SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY } static final days[] order = { days.SUNDAY, days.MONDAY, days.TUESDAY, days.WEDNESDAY, days.THURSDAY, days.FRIDAY, days.SATURDAY }; days Today; Week(days toSetTo){ @SuppressWarnings("unused") days Today = toSetTo; } }

the error is on Main.java:6

Now is the time to start using Java code conventions; they make communication much simpler. Capitalize classes (including enums), constants in ALL_CAPS, variables in camelCase. — chrylis -cautiouslyoptimistic-
– chrylis -cautiouslyoptimistic-, Commented Aug 29, 2016 at 19:25
You are declaring two variables for Today, one variable is local to the constructor, and the other is the instance variable. You should always use this.varName to reference an instance variable. — castletheperson
– castletheperson, Commented Aug 29, 2016 at 19:27

rohitvats · Accepted Answer · 2016-08-29 19:24:12Z

The following is failing at runtime:

myWeek.Today.toString()

because myWeek.Today is null.

In your constructor instead of:

days Today = toSetTo;

you need to do this:

Today = toSetTo;

Roland Illig · Accepted Answer · 2016-08-29 19:25:45Z

You should have fixed the unused warning properly instead of suppressing it. Remove the word days in that line. And look closely at the colors of the variables in Eclipse. They tell you which names belong to each other.

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