Why do different Exceptions occur?

Question

I am using the below code. The first line is giving java.lang.NumberFormatException, and the second is giving java.lang.NullPointerException. I'm unable to figure out why.

int intValue =Integer.parseInt(null);
Double double1 = Double.parseDouble(null);

Answer 1

Because thats how they are implemented,

int intValue =Integer.parseInt(null);

If we look the parseInt implementation, they are throwing NumberFormatException if the input string is null

And Double double1 = Double.parseDouble(null);

In parseDouble(String s) method there is another method call i.e FloatingDecimal.readJavaFormatString(s).doubleValue();
In readJavaFormatString(s) method is where exactly NullPointerException is thrown

FloatingDecimal.readJavaFormatString(s) method