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Or just let them alone or throws an exception?
If the third one, how can I sort elements in ArrayList saving the old order of priority equal elements?
Thanks in advance.
From the documentation:
This sort is guaranteed to be stable: equal elements will not be reordered as a result of the sort.
To save the order of the old arraylist, simply make a copy of the arraylist ahead of time. You can do this by saying:
List<Integer> oldListOrder = new ArrayList<Integer>(listToBeSorted);
Collections.sort(listToBeSorted);
Keep in mind the elements will reference the same objects in both lists. That may not affect you, it depends on what you do next.
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I am somewhat new to Java, so excuse this really dumb question. I was just wondering, how does one declare a 2D array of ImageIcons?
Say like this:
ImageIcon[][] arr = new ImageIcon[10][5];
Note that after this line, the array elements will be uninitialized (they will be all equal to null).
If you want to initialize them, you need to loop through your array and call some of the ImageIcon constructors e.g.
arr[i][j] = new ImageIcon();
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I have an ArrayList whose each element is of type DataType, where DataType is a class:
class DataType{
String dId;
String dType;
String rId;
}
I need to remove all such elements from the list whose rId is equal to any other element's dID.
i.e. if DataType D1 has value of dID as "abc" and DataType D2 has value of rID as "abc", than remove both D1 and D2 from the list.
Could someone please suggest the most appropriate approach for doing this.
The easiest would be to traverse the list once and create a HashMap<String, List<DataType>>.
You will map every object to their dID which forms the primary key.
After that you can iterate over your ArrayList, check the rId of the current object and see if it's in the HashMap. HashMap has O(1) lookup time so this should be a non issue. If the value is present, remove the current value (you're using an Iterator to prevent a ConcurrentModificationException) and remove the objects inside the value-part of the key-value pair as well.
Make sure you have correctly implemented .equals(Object o) and .hashcode().
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I want to detect the file structure in a string.
e.g
if I have a string as /name/test/testme/2 I should be able to store it in a arraylist as different elements like {[name],[test],[testme],[2]}
String[] elements = "/name/test/testme/2".split("/");
More info can be found in the String.split() Javadoc
As Lukas pointed out, (please give him some upvoting) you should use the split method.
String[] elements = "/name/test/testme/2".split("/");
The regular expressions are not used to split strings in sections. Regular expressions are used for matching the target string with a specific generic format. In this case a boolean value indicating if the strings match is returned.
Hope I helped!
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Say the ArrayList is empty before. Then I add one object to the ArrayList at index 1,000,000.
Will the ArrayList create 1,000,001 pointers or just create one pointer?
An IndexOutOfBoundsException will be thrown:
IndexOutOfBoundsException - if the index is out of range (index < 0 ||
index > size())
http://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html#add(int, E)
Since you ask, you haven't even tried to run it. You will get a IndexOutOfBounds exception.
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Is it possible to assign information to an element in an array in java?
For example, can I have an element containing a title and a number etc?
How do you go about this? thanks
Yes, instead of having an array of primitive types (like ints) or Strings, define your own class and then create an array of that. Then you can have whatever information you want in there.
Alternatively, if the array must be an array of primitives or Strings because some other method requires it to be in that form, you could either create a second array like that on demand, or use a second array for the associated data (again you might create your own class for this).