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Java Forum / General / November 2005Is there a goto statement (or something similar)?
Is there a goto statement or something similar in java? If so, how do I use it? >Is there a goto statement or something similar in java? The statements "switch" or "throw" do something similar. >If so, how do I use it? See http://java.sun.com/docs/books/jls/third_edition/html/j3TOC.html >The statements "switch" or "throw" do something similar. "switch" and "throw" are not statements, but keywords. A more appropriate wording might be "The switch- and the throw-statement do something similar." >>The statements "switch" or "throw" do something similar. > > "switch" and "throw" are not statements, but keywords. > > A more appropriate wording might be > "The switch- and the throw-statement do something similar." ?? Your sentence version is virtually identical. Regardless, it is a pointless argument of semantics over an exceptionally simple question. -- LTP :) On Sat, 12 Nov 2005 17:05:43 -0500, "Mike42" <michael_adamus@nospam.yahoo.com> wrote, quoted or indirectly quoted someone who said : >Is there a goto statement or something similar in java? If so, how do I >use it? Break. It lets you leap out of a loop or loop nest. See http://mindprod.com/jgloss/jcheat.html  SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. > On Sat, 12 Nov 2005 17:05:43 -0500, "Mike42" > <michael_adamus@nospam.yahoo.com> wrote, quoted or indirectly quoted [quoted text clipped - 6 lines] > > See http://mindprod.com/jgloss/jcheat.html Actually, break is much more powerful then that. break lets you terminate any instruction abruptly. You need not even be inside any block construct: label: break label; is a perfectly legal no-op. SignatureYou can't run away forever, But there's nothing wrong with getting a good head start. --- Jim Steinman, "Rock and Roll Dreams Come Through" > Is there a goto statement or something similar in java? If so, how do I > use it? There is no goto per se (though the the keyword is reserved), but break and continue statements cause unconditional branching in more restrictive contexts. You can combine them with statement labels to achieve many of the effects that it is reasonable to want goto for. As Stefan Ram pointed out, a switch block or a throw statement also produce branching. So does a try/catch/finally, an if, a for or while loop, or a method invocation. SignatureJohn Bollinger jobollin@indiana.edu On Sat, 12 Nov 2005 17:05:43 -0500, "Mike42" <michael_adamus@nospam.yahoo.com> wrote, quoted or indirectly quoted someone who said : >Is there a goto statement or something similar in java? If so, how do I >use it? In the JVM of course there are jumps and conditional jumps. Part of what the byte code verifier does is make sure the stack is consistent no matter which way you jump, and to make sure you don't jump into the middle of an instruction or outside the method. SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. > Is there a goto statement or something similar in java? If so, how do I > use it? At the risk of sounding like an old geezer, every programming course I have taken in over 20 years of professional programming has strongly discouraged the use of 'goto' statements. Every experienced programmer I have met in that time has had the same view, based on their own experiences with the unmaintainable mess that results: 'goto' statements are evil. Luckily, Java doesn't have a 'goto' but, even if it did, you should avoid it like the plague. Ditto for 'goto' in any other programming language. Rhino > At the risk of sounding like an old geezer, every programming course I > have taken in over 20 years of professional programming has strongly > discouraged the use of 'goto' statements. Every experienced programmer I > have met in that time has had the same view, Clearly we have not met ;-) > based on their own > experiences with the unmaintainable mess that results: 'goto' statements > are evil. Interestingly, the C++ source for the native part of the AWT implementation makes heavy use of goto in order to /improve/ the clarity, structure, and maintanability of the code. Works too... -- chris On Sun, 13 Nov 2005 14:38:18 -0000, "Chris Uppal" <chris.uppal@metagnostic.REMOVE-THIS.org> wrote, quoted or indirectly quoted someone who said : >Interestingly, the C++ source for the native part of the AWT implementation >makes heavy use of goto in order to /improve/ the clarity, structure, and >maintanability of the code. Works too... Is it mechanically generated code? SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. > > At the risk of sounding like an old geezer, every programming course I > > have taken in over 20 years of professional programming has strongly [quoted text clipped - 10 lines] > makes heavy use of goto in order to /improve/ the clarity, structure, and > maintanability of the code. Works too... I like to think I'm an open-minded guy so I'm willing to concede that 'goto' might possibly be a worthwhile construct _if used correctly in a limited number of circumstances_ like the ones that you suggest. Honestly, I've never much thought about using 'goto' because of all the anti-goto propaganda I've heard from Day One of my professional programming days. I *think* the anti-goto advice is primarily a reaction by structured programmers to the preceding era of programming. My impression is that the previous less-sophisticated philosophy of programming valued conciseness of code above all so many people wrote short blocks of code and then used goto statements to branch to them, wherever they were, to keep programs small. The result soon became known - disparagingly - as spaghetti code. The "new" generation of structured programmers turned up their noses at spaghetti code and decreed the 'goto' statement the chief culprit and insisted that it never be used. (Actually, in our COBOL shop, 'goto' *was* permitted for one special case: to go to the last section in the paragraph, which invariably contained a single 'exit' statement.) So maybe the taboo against 'goto' is a bit dated. Perhaps it would be fair to say that the goto is a reasonable statement to use for certain circumstances and then carefully enumerate those cases. But I am so used to avoiding 'goto' that I doubt I'd ever start using it, even if Java had a 'goto' statement; I'm far more used to accomplishing what I want without 'goto'. Maybe I *am* a geezer, like the people who declined to use cars because their old horses worked just fine :-) Rhino On Sun, 13 Nov 2005 16:14:24 -0500, "Rhino" <no.offline.contact.please@nospam.com> wrote, quoted or indirectly quoted someone who said : >I *think* the anti-goto advice is primarily a reaction by structured >programmers to the preceding era of programming. I recall writing a C macro. One way it could be done with goto that required about 1/3 as much code. Yet the boss still wanted to go the long winded way since he knew that goto was bad. SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. > I like to think I'm an open-minded guy so I'm willing to concede that > 'goto' might possibly be a worthwhile construct _if used correctly in a > limited number of circumstances_ like the ones that you suggest. You are the first anti-goto campaigner (please excuse the exgageration) I have ever heard admit that there might be /any/ circumstances where a goto could improve the code. You are indeed "an open-minded guy" ;-) -- chris > Interestingly, the C++ source for the native part of the AWT implementation > makes heavy use of goto in order to /improve/ the clarity, structure, and > maintanability of the code. Works too... I agree here. There are gotos and gotos. While generalizations are very hard, i find that as long as gotos always jump out of scopes, never into, and are "downstream", they hardly ever do serious harm, and can greatly untangle conditionals. :) SignatureYou can't run away forever, But there's nothing wrong with getting a good head start. --- Jim Steinman, "Rock and Roll Dreams Come Through" > Interestingly, the C++ source for the native part of the AWT implementation > makes heavy use of goto in order to /improve/ the clarity, structure, and > maintanability of the code. Works too... Does it? For colour management it does, but not so much elsewhere within AWT. Most uses of goto in the J2SE source are for error handling and resource freeing. Not particularly useful in Java. I don't think it's goto which are the issue. Although it isn't as clear as it might be. The problem is using control flow structures that do not mirror if, for, while, exceptions, etc. Tom Hawtin SignatureUnemployed English Java programmer http://jroller.com/page/tackline/ > Does it? For colour management it does, but not so much elsewhere within > AWT. It seems to be mainly for cleaning up JNI references in code that is not (ultimately) invoked from Java. -- chris >Luckily, Java doesn't have a 'goto' but, even if it did, you should avoid it >like the plague. Ditto for 'goto' in any other programming language. Java uses break and continue, which take a parameter in the same way a goto statement requires. The only difference is that the label must be bound to a loop (allowing to break out to a specific loop, rather than using a hackish sentry value). > Is there a goto statement or something similar in java? If so, how do I > use it? The goto statement is a programming anachronism with almost no surviving use. The one justifiable use I've seen is to cleanly escape deeply nested conditionals within a function. ========================= if (...) { if (...) { if (...) { goto handler; } } } return; handler: cleanup; ========================= However, try/catch blocks are a better substitute: ========================= try { if (...) { if (...) { if (...) { throw new SomeExceptionType(); } } } } catch (SomeExceptionType e) { } ========================= At its most basic level, this construct works similarly to a goto in this case. Exceptions are much more powerful, though, in that unhandled exceptions will propagate up the call stack in a predictable manner until something else handles them. This allows an escape from deeply nested conditionals to travel through the method as well as to outside the method, but in a clean fashion that doesn't require any knowledge of anything outside the method. Your method merely has to declare that it doesn't handle whatever exception type it wants to pass up the stack. ======================= public void myMethod() throws SomeUnhandledException { } ======================= On Sun, 13 Nov 2005 14:55:22 GMT, Tony O'Bryan <storm_reaver@yahoo.com> wrote, quoted or indirectly quoted someone who said : >try > { [quoted text clipped - 12 lines] > { > } you can also do that with: outer: > { > if (...) [quoted text clipped - 3 lines] > if (...) > { break outer; > } > } > } > } // continues here SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. > outer: > > { break/continue only work with loop labels, so you need to make a dummy one around the block, e.g. outer: while(true) { // ... statement incl. break or continue } If you don't need continue, use do .. while(false) instead. >> outer: >> > { [quoted text clipped - 7 lines] > > If you don't need continue, use do .. while(false) instead. Incorrect. class T { void method () { block : { int x = 0; break block; } } } works just fine SignatureYou can't run away forever, But there's nothing wrong with getting a good head start. --- Jim Steinman, "Rock and Roll Dreams Come Through" Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. 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