problems with a TreeSet

i'm implementing a TreeSet, but when i try to add the second element i got NullPointerException and i can't figure out why:confused:. here is my class Month

Code:

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package navigableset;

public class Month implements Comparable<Month> {
        private String name;
        private String number;
       
        public Month(int i, String name) {
                this.number = number;
                this.name = name;
        }
               
        public int compareTo(Month m) {
                return this.number.compareTo(m.number);
        }
       
}

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and here is the class with the main() and where the error happen is when i try to add the object feb:

Code:

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package navigableset;

import java.util.NavigableSet;
import java.util.TreeSet;

public class TreeSetExample {

        public static void main(String[] args) {

                NavigableSet<Month> set = new TreeSet<Month>();
                Month jan = new Month(1, "January");
                Month feb = new Month(2, "February");
               
                set.add(jan);
                set.add(feb);
        }
}

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Quote:

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Originally Posted by j2me64

i'm implementing a TreeSet, but when i try to add the second element i got NullPointerException and i can't figure out why:confused:.

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the bugs were in the class Month, so changing to

Code:

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public class Month implements Comparable<Month> {
        private String name;
        private int number;
       
        public Month(int i, String name) {
                this.number = i;
                this.name = name;
        }
               
        public int compareTo(Month m) {
                Integer i1 = this.number;
                Integer i2 = m.number;
                return i1.compareTo(i2);
        }
}

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also the TreeSet is happy now.