NullPointerException in method returning type Object [duplicate]

Question

Why does the following throw a NullPointerException? :

public static Object myTest() { 
    boolean x = false; 
    boolean y = false; 
    return x && y ? new Object() : x ? x : y ? y : null;
}

public static void main(String [ ] args) {
    myTest(); 
}

I know if i do either of the following the code will not throw a NullPointerException:

A)

public static Object myTest() { 
    boolean x = false; 
    boolean y = false; 
    return x && y ? new Object() : x ? x : y ? y : (Object) null;
}

public static void main(String [ ] args) {
    myTest(); 
}

B)

public static Object myTest() { 
    Boolean x = false; 
    Boolean y = false; 
    return x && y ? new Object() : x ? x : y ? y : null;
}

public static void main(String [ ] args) {
    myTest(); 
}

Also, if i change the code completely and do the following it works:

public static Object myTest() { 
    boolean x = false; 
    boolean y = false; 

    if(x && y) {
        return new Object(); 
    } else if(x) {
        return x; 
    } else if(y) {
        return y;
    } else {
        return null;
    }
}

public static void main(String [ ] args) {
    myTest(); 
}

I guess the compiler is doing some sort of an optimization and somehow messing things up? I'm assuming it's some sort of a casting problem, but why would it throw a NullPointerException in that case instead of a ClassCastException? Any information as to why this is happening would be greatly appreciated!

Thanks in advance

Answer 1

If you add some parenthesis for readability:

return (x && y) ? (new Object()) : (x ? x : (y ? y : null));

You can see that at y ? y : null, the compiler will attempt to unbox null (so that the types match), causing a NPE to be thrown.