Different bugs in LinkedHashMap - java8.1

Question

If I access the keys of a LinkedHashMap<Vector, Vector<Integer>> inside its class it is extracted correctly, but if I create an instance of its class and call a class method that displays the LinkedHashMap, I find some of the fields in the keys that are instances of Vector are missing.

import java.util.Vector;
import java.util.LinkedHashMap;
public class TestLinkedHashMap 
{
 public static void main(String[] args) 
 {
 Test t = new Test();
 t.setSample(); 
 System.out.println("The sample printed in main function is : \n" + t.getSample());
 return;
 }
}
class Test
{
 LinkedHashMap<Vector, Vector<Integer>> sample;
 public Test()
 {
 sample = 
 new LinkedHashMap<Vector, Vector<Integer>>();
 }
 public LinkedHashMap<Vector, Vector<Integer>> getSample()
 {
 return sample;
 }
 public void setSample()
 {
 Vector record1 = new Vector();
 record1.add(new String("Apple"));
 record1.add(new String("Orange"));
 record1.add(new String("Grapes"));
 record1.add(new String("Lime"));
 Vector<Integer> v1 = new Vector<Integer>();
 v1.add(new Integer(0));
 v1.add(new Integer(8));
 v1.add(new Integer(28));
 System.out.println("sample = " + sample);
 sample.put(new Vector(record1), v1);
 Vector record2 = new Vector();
 record2.add(new String("Pineapple"));
 record2.add(new String("Pear"));
 record2.add(new String("Mango"));
 Vector<Integer> v2 = new Vector<Integer>();
 v2.add(new Integer(0));
 v2.add(new Integer(18));
 sample.put(new Vector(record2), v2);
 System.out.println("The sample printed inside the class is : \n" + sample);
 }

Above code works fine, but in the application I am developing, I am getting different outputs for the sample. I have included the output of my application below. My application is using LinkedHashMap in similar manner as above.

Output is different in real application

• Jai: In general, it's a bad idea to use something mutable as key. You are messing up the hashes in the hashmap. The documentation explicitly warned you not to use something mutable as the key.
• user3322178: I think you maybe right, then only solution would be to convert the Vector to string and store it as a key.
• Dreamspace President: Random thought: Maybe OP could just use the toString output of the Vector objects as keys, because I think those don't ever change.
• Harald: Side note: if you don't need the thread-safety of Vector, ArrayList is preferred (says the javadoc of Vector).

Answer 1

Of course this.sample is null. You never set it to a value. In the constructor, you’re creating a new LinkedHashMap<Vector, Vector<Integer>> , but not actually assigning it to the class member variable sample, instead you’re just creating a local variable (local to the constructor) called sample.

Remove the LinkedHashMap<Vector, Vector<Integer>> before sample in the constructor and that will initialize the class member variable sample as expected.

• user3322178: deleted the redeclaring of sample