Tilted Forum Project Discussion Community  

Go Back   Tilted Forum Project Discussion Community > Interests > Tilted Technology


 
 
LinkBack Thread Tools
Old 04-16-2004, 03:39 PM   #1 (permalink)
Psycho
 
[java] "if" problem

Please ignore my poor formatting and my bad way of doing things. At the time of writing I have about an hours experience with java, and I am a tad stuck with this code I have written.


class maths
{
public static void main (String args[])
{
int x;
x = Integer.parseInt(args[0]) ;
int y;
y = Integer.parseInt(args[2]) ;
System.out.println (x*y) ;
String f;
f = (args[1]);
if (f == "x")
System.out.println (x*y);
else
System.out.println ("Sorry, I only do multiplication");
}
}


OK, the idea is I enter in the command line
java maths 3 x 4
and it returns
12 (as a test, to make sure that my casting and maths were right)
12 (because I have an "x" as args[1])

Or I enter
java maths 3 / 4
and it returns
12 (as the test)
Sorry, I only do multiplication

What happens is that it compiles perfectly, then:

% java maths 3 x 3
9
Sorry, I only do multiplication

% java maths 3 / 3
9
Sorry, I only do multiplication

I am at a loss.

Also, is there a better way of taking a string from args and turning it into an int?

Thanks all.

Last edited by TheBrit; 04-17-2004 at 02:20 AM..
TheBrit is offline  
Old 04-16-2004, 07:47 PM   #2 (permalink)
Crazy
 
The big error is that in your if statement, you are using == instead of .equals to do the comparison. == only works for primitive data types. Since a String is a referential data type, you have to use .equals.

So,

if( args[ 1 ].equals( "x" ) )
...


As far as taking a String argument and casting it to an int, Integer.parseInt works pretty well.
__________________
"Even if you prove me wrong, I'm not going to believe you." - A. McGill
firebirdta is offline  
Old 04-16-2004, 10:43 PM   #3 (permalink)
Free Mars!
 
feelgood's Avatar
 
Location: I dunno, there's white people around me saying "eh" all the time
Just to add to firebirdta's solution. He is right about the primitive data types and the referential data types.

What you did was trying to do it in the middle way.

When I first saw your if statement, I thought you were evaluating chars but were actually doing strings.

Another possible solution is
if(args[1].charAt(0) == 'x')

Either way works, it just a matter of what kind of data you're dealing with.

The equal method actually deals with object which is another type of referential data types.

Other possible solutions are

if(args[1].equalsIgnoreCase("x"))

In this case, 2 strings are compared regardless of case size.

But one problem with firebirdta's solution. What if the user decides to use the bigger case X? (eg: "java maths 3 X 4" instead of "java maths 3 x 4") Then your if statement would return false since it is only looking for the lower case x. In this case, I suggest you use the if(args[1].equalsIgnoreCase("x"))

One of the fundamentals of data structuring and alogrithms is the ability to predict human behavoior involved when it comes to running programs. Programmers are actually expected to build foolproof programs, meaning that we try to anticptate all possible situation that occurs when the user use the program.

A elite programmer once said

"Programming is an race between the universe and programmers. Programmers build bigger, better and more idiot-proof programs while the universe produce more idiots. So far, the universe is winning"
__________________
Looking out the window, that's an act of war. Staring at my shoes, that's an act of war. Committing an act of war? Oh you better believe that's an act of war
feelgood is offline  
Old 04-17-2004, 02:23 AM   #4 (permalink)
Psycho
 
Ah-hah!
It all works perfectly now, I think I am starting to like this language enough to pick up the O'Reilly book, or whatever book my local library has.
Thanks all.
TheBrit is offline  
Old 04-17-2004, 11:06 AM   #5 (permalink)
Once upon a time...
 
Quote:
Originally posted by TheBrit
Ah-hah!
It all works perfectly now, I think I am starting to like this language enough to pick up the O'Reilly book, or whatever book my local library has.
Thanks all.
try this one:
http://www.mindview.net/Books/TIJ/
It's free
__________________
--
Man Alone
=======
Abstainer: a weak person who yields to the temptation of denying himself a pleasure.
Ambrose Bierce, The Devil's Dictionary.
manalone is offline  
 

Tags
java, problem


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -8. The time now is 12:00 AM.

Tilted Forum Project

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
© 2002-2012 Tilted Forum Project

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360