In my Java program, I get NullPointerException in my HashMap even after initialising and putting values to the HashMap

Question

In my Java program, I get NullPointerException in my HashMap even after initialising and putting values to the HashMap.

    LinkedHashMap<Short,BigInteger> ft = new LinkedHashMap<Short,BigInteger>(5);

    ft.put( (short) 1, BigInteger.valueOf(A));
    ft.put( (short) 2, BigInteger.valueOf(B));
    System.out.println(ft.isEmpty());
    System.out.println(ft.get((short)1));
    System.out.println(ft.get((short)2));
    System.out.println(ft.containsKey(1));
    System.out.println(ft.containsValue(1));

Answer 1

If A or B are of type Long (or Short or Integer) and contain null, that explains the exception (since BigInteger.valueOf() expects a long, and if you pass it some reference numeric type, it unboxes it to a primitive type, which would cause NullPointerException if the Long/Integer/Short is null).

I tried to replace A and B with non null values and tested your code, and got no exception, so this must be it.

You can reduce your code to :

BigInteger.valueOf(A);
BigInteger.valueOf(B);

and still get the exception.