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Java Forum / General / January 2008Array Checking in Java.
I want to know is it possible to do Array Calculation in one step? FIRST _________ Say I have array[100]; I want to assign each of them a Value of 0; In just 1 step. Currently I use for loop to assign each array element. But I think there should be some way to initialize all elements to 0. Does java initializes all elements to 0. When we have not assigned or give it a null Value? SECOND -------------- Further I use an Array like xx[i][j]=99; Here I have to first verify that i & j are between 0-10; So I use if ((i>0)&&(i<10)&&(j>0)&&(j<10)) xx[i][j]=99; But What I want is since Java itself checks out of Bounds, Instead of Hanging when i<0 or i>10 It just skip it. So my Code will work just like xx[i][j]=99; and when out of Bounds Ocur it just skip that instead of hanging. Can it be done? That is Java do not hang when out of bound happens but just skip it and go to next iteration Something like. if (xx[i][j]=99;) === (Out of Bound) break; else proceed further. Can this be done in java? THIRD -------- Is it possible to use Arrays as Sets. And do Union, Intersect, and other things we do in Set Theory. Say we have two arrays of Booleans. BB1[] U BB2[] Gives Union of BB1 and BB2 BB1[] XOR BB2[] Give XOR for the Booleans? Is it Possible? Bye Sanny Sanny, 10.01.2008 10:38: > Say I have array[100]; I want to assign each of them a Value of 0; In > just 1 step. int[] myarray = new int[100]; Java gurantees the initialization with 0. Check the language specification. > SECOND > -------------- > Something like. > > if (xx[i][j]=99;) === (Out of Bound) break; else proceed further. Can > this be done in java? You should catch the ArrayIndexOutOfBoundsException > THIRD > -------- > > Is it possible to use Arrays as Sets. And do Union, Intersect, and > other things we do in Set Theory. No, you need to use a Set. They offer these methods. > > Say I have array[100]; I want to assign each of them a Value of 0; In > > just 1 step. [quoted text clipped - 3 lines] > Java gurantees the initialization with 0. > Check the language specification. What about char array? char[] chararray = new char[100]; I want all of them to be ' '; Will they be done automatically? Can I change the default parameter to something else? > > SECOND > > -------------- [quoted text clipped - 4 lines] > > You should catch the ArrayIndexOutOfBoundsException Will it be as fast as checking just one condition without wasting much time writing out the error? So that I can avoid Checking myself? > > THIRD > > -------- [quoted text clipped - 3 lines] > > No, you need to use a Set. They offer these methods. How to initialize a set? Currently I have two array int[] array1 = new int[100]; int[] array2 = new int[100]; How to convert them to Set and use Set Theory. How fast will they work When I use Union/ XOR/ etc. Will they be performed in one step? And will the speed improve? Bye Sanny Sanny, 10.01.2008 11:18: >>> Say I have array[100]; I want to assign each of them a Value of 0; In >>> just 1 step. [quoted text clipped - 4 lines] > > What about char array? Check the language specification it's all documented there: <http://java.sun.com/docs/books/jls/third_edition/html/j3TOC.html> >>> if (xx[i][j]=99;) === (Out of Bound) break; else proceed further. Can >>> this be done in java? >> You should catch the ArrayIndexOutOfBoundsException > > Will it be as fast as checking just one condition without wasting much > time writing out the error? So that I can avoid Checking myself? The bounds will always be checked by Java. There is no way to disable this. Again read the language specs. >>> Is it possible to use Arrays as Sets. And do Union, Intersect, and >>> other things we do in Set Theory. >> No, you need to use a Set. They offer these methods. > > How to initialize a set? > Currently I have two array > > int[] array1 = new int[100]; > int[] array2 = new int[100]; > > How to convert them to Set and use Set Theory. Check the Javadocs for the different implementations of Set. Basically it's: Set<Integer> set1 = new HashSet<Integer>(100) but that will not add any entries to the set. As I said: you have to read the docs. > How fast will they work When I use Union/ XOR/ etc. Will they be > performed in one step? And will the speed improve? Definitely not "in one step". I have no idea if your speed will "improve". Firstly because I have no idea what your current code does, and secondly because I have no idea what you new code will do). You will need to test that for yourself. If we are talking about 100 items per set, I wouldn't be concerned about the speed. Thomas Sanny skrev: >>> Say I have array[100]; I want to assign each of them a Value of 0; In >>> just 1 step. [quoted text clipped - 9 lines] > I want all of them to be ' '; Will they be done automatically? Can I > change the default parameter to something else? See Arrays.fill(char[] a, char val): http://java.sun.com/j2se/1.5.0/docs/api/java/util/Arrays.html#fill(char[],%20char) > Sanny skrev: >>>> Say I have array[100]; I want to assign each of them a Value of 0; In [quoted text clipped - 13 lines] > See Arrays.fill(char[] a, char val): > http://java.sun.com/j2se/1.5.0/docs/api/java/util/Arrays.html#fill(char[],%20char) To the OP: this is a convenience method - it isn't "one step" at the low level, but it is "one step" in your application code.  SignatureLew > Sanny skrev: >>>> Say I have array[100]; I want to assign each of them a Value of 0; In [quoted text clipped - 13 lines] > See Arrays.fill(char[] a, char val): > http://java.sun.com/j2se/1.5.0/docs/api/java/util/Arrays.html#fill(char[],%20char) Arrays also has asList() <http://java.sun.com/javase/6/docs/api/java/util/Arrays.html#asList(T...)> method, which can be combined with a Set's collection-arg constructor to create the equivalent Set. This example uses Character instead of char to obtain object-ness. When building a Character array, avoid autoboxing from primitive [] inside a method argument. That's why the Character [] is built prior to the Arrays.asList() call. Character [] kars = { '0', 'Z', '-' }; Set <Character> karacters = new HashSet <Character> ( Arrays.asList( kars )); SignatureLew On Thu, 10 Jan 2008 01:38:47 -0800 (PST), Sanny <softtanks@hotmail.com> wrote, quoted or indirectly quoted someone who said : >I want to know is it possible to do Array Calculation in one step? see http://mindprod.com/jgloss/array.html particularly http://mindprod.com/jgloss/array.html#METHODS where it mentions fill. SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com On Thu, 10 Jan 2008 01:38:47 -0800 (PST), Sanny <softtanks@hotmail.com> wrote, quoted or indirectly quoted someone who said : >But What I want is since Java itself checks out of Bounds, Instead of >Hanging when i<0 or i>10 It just skip it. So my Code will work just >like xx[i][j]=99; and when out of Bounds Ocur it just skip that >instead of hanging. Can it be done? Yes, just catch the ArrayIndexOutOfBoundsException and print an error message or whatever you planned to do in your if checks. SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com On Thu, 10 Jan 2008 01:38:47 -0800 (PST), Sanny <softtanks@hotmail.com> wrote, quoted or indirectly quoted someone who said : >BB1[] U BB2[] Gives Union of BB1 and BB2 > >BB1[] XOR BB2[] Give XOR for the Booleans? no. Have a look at http://mindprod.com/jgloss/enumset.html for mathematical set operations. You might also look at the Collections that implement the Set interface. see http://mindprod.com/jgloss/set.html SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com > [...] > Further I use an Array like [quoted text clipped - 9 lines] > like xx[i][j]=99; and when out of Bounds Ocur it just skip that > instead of hanging. Can it be done? Yes. You'll find a description of the technique in "Effective Java" by Joshua Bloch -- given as an example of something that is possible but that you should NOT do. Here is Bloch's example code: // Horrible abuse of exceptions. Don't ever do this! try { int i = 0; while(true) a[i++].f(); } catch(ArrayIndexOutOfBoundsException e) { } If you doubt the truth of the comment, I suggest you get the book and read Bloch's reasons -- there's a lot of other good stuff in that book, and it's worth having in any case. SignatureEric Sosman esosman@ieee-dot-org.invalid 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. Read more ...
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