在将值null的Integer变量分配给int变量后，为什么会得到NPE？

Question

I want to know how the compiler reads this code.

public class obj {
    public static void main(String[] args) {
        Integer obj = null; //line4
        int x = obj;   //line 5
        System.out.println(x); //line6  
    }
}

My understanding is that line 5 can do auto unboxing which means it converts the Integer type to primitive int .

But I am not calling any method on x , just printing. Why is it giving me a NullPointerException ?.

Answer 1

Autoboxing here means that

int x = obj; 

is actually:

int x = obj.intValue();

and hence the NullPointerException, as obj is null.

Answer 2

Java有一种称为自动装箱的东西，其中Integer对象会自动转换为int原始类型。

Answer 3

看一下字节码

javap -c com.interviews.practise.obj