Programming Forums > Application Development > Java

lectricpharaoh · Jul 27th, 2007, 11:48 PM

Yes, you've got it, except Java does not interpret 01000000 as being true. You need an explicit comparison when testing any value that is not boolean. Otherwise, you get a compiler error:

(Toggle Plain Text)

int flag = 0;
if(flag != 0)
  System.println("flag is nonzero");
if(flag)  // error
  System.println("flag is nonzero");

The second if() is a problem because it evaluates to this:

(Toggle Plain Text)

if(flag == true)  // error
  System.println("flag is nonzero");

This is comparing an int and a boolean, so you have a type mismatch, and the compiler will choke. But on the boolean operations stuff, it seems you're clear.

357mag · Jul 28th, 2007, 4:36 AM

Kinda confusing. In C++ any non-zero integer means true, and zero means false. I think I did read in one of my books about Java that in Java the zero does not mean false and any non-zero integer does not necessarily mean true. I thought the if statement always tests for truth. So if I did this in Java:

(Toggle Plain Text)

int x = 1;

if (x)
   System.out.print("Welcome home.");

else
   System.out.print("Go away.");

That would be wrong? I would have to say:

(Toggle Plain Text)

int x = 1;

if (x == 1)
   System.out.print("Welcome home.");

else
   System.out.print("Go away.");

I'm going to have to play around with this stuff.

357mag · Jul 28th, 2007, 5:22 AM

So just by itself, the result 1000 0000 doesn't necessarily mean true to Java. You have to go one step further and include a comparison operator in your if statement like this:

(Toggle Plain Text)

if (result != 0)
   System.out.print("This line will execute.");

else
   System.out.print("You won't see this.");

The end result of explicitly adding the != operator to your if statement is that Java will actually compare the result(1000 0000) to 0(!= 0) and then the end result of that will in fact be either a true or a false, meaning the outcome will be in fact a boolean value. Then the compiler will go ahead and execute the appropriate line. God I hope I got this correct.

lectricpharaoh · Jul 28th, 2007, 7:32 AM

Quote:

Originally Posted by 357mag

So just by itself, the result 1000 0000 doesn't necessarily mean true to Java. You have to go one step further and include a comparison operator in your if statement like this:

Exactly. Without it, I believe Java will consider the code to be a compile-time error. Why not try and see?

Jul 27th, 2007, 11:48 PM	#11
lectricpharaoh Caffeinated Neural Net Join Date: Jun 2005 Location: Wet west coast of Canada Posts: 889 Rep Power: 4	Yes, you've got it, except Java does not interpret 01000000 as being true. You need an explicit comparison when testing any value that is not boolean. Otherwise, you get a compiler error: (Toggle Plain Text) int flag = 0; if(flag != 0) System.println("flag is nonzero"); if(flag) // error System.println("flag is nonzero"); int flag = 0; if(flag != 0) System.println("flag is nonzero"); if(flag) // error System.println("flag is nonzero"); The second if() is a problem because it evaluates to this: (Toggle Plain Text) if(flag == true) // error System.println("flag is nonzero"); if(flag == true) // error System.println("flag is nonzero"); This is comparing an int and a boolean, so you have a type mismatch, and the compiler will choke. But on the boolean operations stuff, it seems you're clear. __________________ A man's knowledge is like an expanding sphere, the surface corresponding to the boundary between the known and the unknown. As the sphere grows, so does its surface; the more a man learns, the more he realizes how much he does not know. Hence, the most ignorant man thinks he knows it all. - L. Sprague de Camp

Jul 28th, 2007, 4:36 AM	#12
357mag Hobbyist Programmer Join Date: Mar 2005 Posts: 148 Rep Power: 4	Kinda confusing. In C++ any non-zero integer means true, and zero means false. I think I did read in one of my books about Java that in Java the zero does not mean false and any non-zero integer does not necessarily mean true. I thought the if statement always tests for truth. So if I did this in Java: (Toggle Plain Text) int x = 1; if (x) System.out.print("Welcome home."); else System.out.print("Go away."); int x = 1; if (x) System.out.print("Welcome home."); else System.out.print("Go away."); That would be wrong? I would have to say: (Toggle Plain Text) int x = 1; if (x == 1) System.out.print("Welcome home."); else System.out.print("Go away."); int x = 1; if (x == 1) System.out.print("Welcome home."); else System.out.print("Go away."); I'm going to have to play around with this stuff.

Jul 28th, 2007, 5:22 AM	#13
357mag Hobbyist Programmer Join Date: Mar 2005 Posts: 148 Rep Power: 4	So just by itself, the result 1000 0000 doesn't necessarily mean true to Java. You have to go one step further and include a comparison operator in your if statement like this: (Toggle Plain Text) if (result != 0) System.out.print("This line will execute."); else System.out.print("You won't see this."); if (result != 0) System.out.print("This line will execute."); else System.out.print("You won't see this."); The end result of explicitly adding the != operator to your if statement is that Java will actually compare the result(1000 0000) to 0(!= 0) and then the end result of that will in fact be either a true or a false, meaning the outcome will be in fact a boolean value. Then the compiler will go ahead and execute the appropriate line. God I hope I got this correct.

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