Null Pointer exception when accessing a static instantiated object with in the instance of

[Kalyana Chakravathy]

I am facing one weird problem when accessing a static object instance,

Test.java:

import java.util.*;

public class Test {
        private static Test instance = new Test();
        private static Map<String, String> map = new HashMap<String, String>();
        private Test() {
                enter();
        }
        private void enter() {
                map.put("dummy1","dummy2");
        }
        public static Test getinstance() {
                return instance;
        }
        public static void display() {
                System.out.println("Key = dummy1, Value = "+map.get("dummy1"));
        }
}

Run.java

public class Run {
        public static void main(String[] args) {
                Test.display();
        }
}

On running Run it gives me a NPE,

[jkalyana@toddler ~]$ javac Test.java
[jkalyana@toddler ~]$ vim Run.java
[jkalyana@toddler ~]$ javac Run.java
[jkalyana@toddler ~]$ java Run
Exception in thread "main" java.lang.ExceptionInInitializerError
at Run.main(Run.java:3)
Caused by: java.lang.NullPointerException
at Test.enter(Test.java:10)
at Test.<init>(Test.java:7)
at Test.<clinit>(Test.java:4)
... 1 more


I had a doubt and changed the Test.java to this,

import java.util.*;

public class Test {
        private static Map<String, String> map = new HashMap<String, String>();
        private static Test instance = new Test();
        private Test() {
                enter();
        }
        private void enter() {
                map.put("dummy1","dummy2");
        }
        public static Test getinstance() {
                return instance;
        }
        public static void display() {
                System.out.println("Key = dummy1, Value = "+map.get("dummy1"));
        }
}

On moving the declaration of Test below map, it runs,

[jkalyana@toddler ~]$ java Run
Key = dummy1, Value = dummy2

Can anyone tell me why this is so.

[Rob Spoor]

Pleaseuse one thread per question. Let's continue here.