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how much $$ is in your buget? We might need it all.
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Hi all,
Near one or two years (version Java at that time is 1.5x), I have a short code to compare 2 Strings in java like bellow:
String a = "abc";
String b ="abc";//this is load from the database.
CODE 1
if(a==b){
System.out.println("equal");
}else {
System.out.println("dif");
}
and I got the result is dif
I remember because after I change the code to
String a = "abc";
String b ="abc";//this is load from the database.
CODE 2
if(a.equals(b)){
System.out.println("equal");
}else {
System.out.println("dif");
}
It give me the result is equal
Is it true or my eyes is wrong?
Now the CODE 1 always gives the result is equal
modified 17 Feb '12.
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This is as expected, in Java there is no operator overloading and == always does a reference equality check. To do a value equality check, you need to use .equals (after doing a null check).
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Code1 compares the objects and if they are equal, also both Objects have the same value they are still different objects.
Code2 checks character wise for the value.
It's a common failure.[^].
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sharkbc wrote: Now the CODE 1 always gives the result is equal
Is it true or my eyes is wrong?
Java, regardless of version, has always operated in that way (equals is required.)
So something is wrong in how you are validating this.
Perhaps because despite what your comment says you are not in fact loading it from the database. (An very odd corner case would involve how you are 'loading' it from the database and would indicate an error in the load process.)
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hi Jschell,
I've just modify my question, it must be
...
Is it true or my eyes is wrong?
Now the CODE 1 always gives the result is equal
Im sure at that time, the database is not change and i do not change any other code in the programe, because after we got the mistake, we debug the code and get it.
We just only change if(a==b) to if(a.equals(b))
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The real problem is that we do not know what you are actually doing.
Again the following has always been true regardless of java version for the major java vendors...
Equality compares references
The method equals() compares value (content of string.)
As I said there are ways which MIGHT present seemingly different results dependent on the specifics of what is going on. But you haven't presented the specifics.
And based ONLY on the code you posted you are comparing references for what you refer to "CODE 1". And reference equality will be equal.
So what are some possible causes for some other difference for some OTHER code?
1. You were not using a real version of java, it was some odd variant.
2. There was something odd about the way in which your database code worked.
3. There was something odd about your data
4. You misinterpreted what was happening before.
5. The real code would make it explicitly obvious why a difference was occurring.
6. The method intern() was being called somewhere (incorrectly called.)
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Where is a initialised from? It is possible that the two objects are the same and then == will return true.
For future reference, if you want to compare two objects always use the equals() method.
Panic, Chaos, Destruction. My work here is done.
Drink. Get drunk. Fall over - P O'H
OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre
I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer
Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett
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sir i need to compress a video file dont know how to compress a video file in java. thanks in advace....
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Firstly, remove your duplicate question above.
Secondly, a quick search[^] will get more information then a generic question here.
Panic, Chaos, Destruction. My work here is done.
Drink. Get drunk. Fall over - P O'H
OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre
I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer
Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett
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Hello,
Nice to see a knowledgeable and very helping web site.. I am new member in Java. But i am perfect programmer. I am interested in Java language ,, kindly guide me .. if anyone respond to me i shall be very thankful.
Ch. Kashif Nadeem
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Start here[^], and if you have a more specific question then please ask it.
Unrequited desire is character building. OriginalGriff
I'm sitting here giving you a standing ovation - Len Goodman
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Message Automatically Removed
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Message Automatically Removed
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Message Automatically Removed
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need java code for image segmentation
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That's nice. Have you tried writing something?
Panic, Chaos, Destruction. My work here is done.
Drink. Get drunk. Fall over - P O'H
OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre
I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer
Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett
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List<ImageSegment> segments = image.doSegmentation();
The implementation of doSegmentation is left as an exercise for the reader.
(Seriously, what sort of idiocy does it take to think that you can ask a one line, poorly formatted request for someone to do your entire project, and get anything other than downvotes and sarcastic responses?)
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List<OrderedPair> list1 = new ArrayList<OrderedPair>() ;
OrderedPair e0 = new OrderedPair(); e0.index=0; e0.value=1;
OrderedPair e1 = new OrderedPair(); e1.index=2; e1.value=2;
OrderedPair e2 = new OrderedPair(); e2.index=3; e2.value=3;
ListIterator<OrderedPair> iterator = list1.listIterator();
iterator.add(e0);
iterator.add(e1);
iterator.add(e2);
OrderedPair op1 = (OrderedPair) iterator.previous();
System.out.print("index = "); System.out.print(op1.index);
System.out.print(", value = "); System.out.print(op1.value);
System.out.println();
OrderedPair op2 = (OrderedPair) iterator.previous();
System.out.print("index = "); System.out.print(op2.index);
System.out.print(", value = "); System.out.print(op2.value);
System.out.println();
OrderedPair op3 = (OrderedPair) iterator.previous();
System.out.print("index = "); System.out.print(op3.index);
System.out.print(", value = "); System.out.print(op3.value);
System.out.println();
Above is the code block which works fine on one system but the previous() method on some other system doesnt move the iterator backwards and results in the same object .
Any idea why such a behaviour?
Pritha
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does that throw an exception? (NuSuchElementException)
Why do you add via the iterator? you can add directly to the ArrayList.
It might also be useful to OOP that code.
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thanks for your reply
it doesnt throw an exception.
The problem is it works on one system and doesnt work on another.
should i reinstall eclipse or java libraries.
thanks
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check the runtime, there might be the difference.
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