Boolean.valueOf() produces NullPointerException sometimes

Question

I have this code:

package tests;

import java.util.Hashtable;

public class Tests {

    public static void main(String[] args) {

        Hashtable

        

Answer 1

Method signature

The method Boolean.valueOf(...) has two signatures:

1. public static Boolean valueOf(boolean b)
2. public static Boolean valueOf(String s)

Your modifiedItems value is Boolean. You cannot cast Boolean to String so consequently the first signature will be chosen

Boolean unboxing

In your statement

Boolean.valueOf(modifiedItems.get("item1"))

which can be read as

Boolean.valueOf(modifiedItems.get("item1").booleanValue())   

However, modifiedItems.get("item1") returns null so you'll basically have

null.booleanValue()

which obviously leads to a NullPointerException