Question

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Any idea why I need to cast an integer literal to (int) here?

package typecastingpkg;

public class Main
{        
    public static void main(String[] args)
    {
       byte a=10;
       Integer b=(int)-a;
       System.out.println(b);

       int x=25;
       Integer c=(Integer)(-x); // If the pair of brackets around -x are dropped, a compile-time error is issued - illegal start of type.
       System.out.println(c);

       Integer d=(int)-a;     //Compiles fine. Why does this not require a pair of braces around -a?
       System.out.println(d);
    }
}

In this code, while casting of -x of primitive type int to a wrapper type Integer, a compile-time error is produced: illegal start of type.

Integer c=(Integer)-x;

It requires a pair of braces around -x like Integer c=(Integer)(-x);

The following expression however compiles fine.

Integer d=(int)-a;

Why does this one not require a pair of braces around -a as in the preceding expression?

Answer 1

The compiler thinks that, in the expression (Integer)-x, you are trying to subtract x from a variable called Integer, hence the error since no such variable is defined. (int)-x works because int is a reserved keyword for a primitive type and cannot be used as a variable name, so the compiler can deduce that you are trying to cast, not subtract.