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

As Andy already very well described the reason of NullPointerException:

which is due to Boolean un-boxing:

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

get converted into:

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

at runtime and then it throw NullPointerException if modifiedItems.get("item1") is null.

Now I would like to add one more point here that un-boxing of the following classes to their respective primitives can also produce NullPointerException exception if their corresponding returned objects are null.

1. byte - Byte
2. char - Character
3. float - Float
4. int - Integer
5. long - Long
6. short - Short
7. double - Double

Here is the code:

    Hashtable modifiedItems1 = new Hashtable();
    System.out.println(Boolean.valueOf(modifiedItems1.get("item1")));//Exception in thread "main" java.lang.NullPointerException

    Hashtable modifiedItems2 = new Hashtable();
    System.out.println(Byte.valueOf(modifiedItems2.get("item1")));//Exception in thread "main" java.lang.NullPointerException

    Hashtable modifiedItems3 = new Hashtable();
    System.out.println(Character.valueOf(modifiedItems3.get("item1")));//Exception in thread "main" java.lang.NullPointerException

    Hashtable modifiedItems4 = new Hashtable();
    System.out.println(Float.valueOf(modifiedItems4.get("item1")));//Exception in thread "main" java.lang.NullPointerException

    Hashtable modifiedItems5 = new Hashtable();
    System.out.println(Integer.valueOf(modifiedItems5.get("item1")));//Exception in thread "main" java.lang.NullPointerException

    Hashtable modifiedItems6 = new Hashtable();
    System.out.println(Long.valueOf(modifiedItems6.get("item1")));//Exception in thread "main" java.lang.NullPointerException

    Hashtable modifiedItems7 = new Hashtable();
    System.out.println(Short.valueOf(modifiedItems7.get("item1")));//Exception in thread "main" java.lang.NullPointerException

    Hashtable modifiedItems8 = new Hashtable();
    System.out.println(Double.valueOf(modifiedItems8.get("item1")));//Exception in thread "main" java.lang.NullPointerException