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I'm converting a hashmap into 2 arrays, an integer array, and a String array. I'm trying to do this to make it usable, my HashMap looks like this:
HashMap<String, String> I'm converting the second string into an integer, and the hashmap is created from what the user puts into the configuration file.
I want to move the first string into an array, and then the second string into another array, how can do that?
in otherwords, when i do hashmap.values() is there a way to get one section, like the first and the the second one later? What's the best way around this?
I thing you basically want to create two arrays one for keys and one for values. You can use map.keySet() to get keys and map.values() to get values. Now you can convert this two into a List or Array.
I want to move the first string into an array, and then the second
string into another array, how can do that?
List<String> keyList= new ArrayList<String>( map.keySet());
List<String> valueList= new ArrayList<String>( map.values());
If you want to convert List as array than,
String[] keyArray=keyList.toArray(new String[keyList.size()]);
String[] valueArray=valueList.toArray(new String[valueList.size()]);
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I have used java ArrayList when I inserted one element in the list and i have converted the validatable response to array list when I used assert equals it is showing that both are different
like one is [abcd] other is [[abcd]]
Validatable response = given().spec(request).filter(new ErrorLoggingFilter(errorPrintStream)).pathParams("","").when.post(endpoint).then()
the response is of the form ArrayList when I printed that It came of the form [[abcd]]
To my knowledge, these two are different things
["abcd"] this means an array has one string "abcd" element.
[["abcd"]] this means an array has one array ["abcd"] element.
Yes, ["abcd"] and [["abcd"]] are completely different. Let us understand why.
Let us consider an array ["abcd"]. As you can see, it contains only one element i.e. "abcd". So this is an array that contains a single string value. Now for [["abcd"]], the outer array contains another array inside of it and the inner array contains "abcd". Though their ultimate content seem to be same, they are absolutely different. One is a string array (an array that contains a string value) and the other is an array of string arrays.
Absolutely different, a one-dimensional array, a two-dimensional array,in many languages,reference form it, [0] and [0][0]
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I am working on a project that has a list of student name and numbers, for example
James Bloggs,1
Paul Jonson,43
Andt Peters,23
Once I have them in an array I then need them sorted.
What is the best way of going about this. Its not the sort Im stuck on its the referencing the names to the numbers. I would have thought if I do a 2 denominational array only one would be sorted.
Any help would be great,
EDIT: I just realized this question was asking about a 2-dimensional array and my answer doesn't directly deal with that. I am skeptical that arrays should be involved at all. Arrays are usually for dealing with primitive data, and maybe if you are coming from a C background you'd think they'd be the natural thing to use. If you really honestly have to use arrays then this probably isn't the way to go.
https://docs.oracle.com/javase/7/docs/api/java/util/TreeMap.html
public void foo(){
// Use a TreeMap. It will sort keys on insertion.
Map<Integer,String> nameByNumber = new TreeMap<>();
nameByNumber.put(1, "James Boggs");
// etc. put all the entries in however you need to
List<Integer> sortedNumbers = personByNumber.getKeys();
List<String> namesSortedByNumber = personByNumber.getNames();
}
If you need it to be more organized and complex, you can encapsulate the name and number into a Class with a name and number property. Then you'd still use the number as the key, but you'd have the full class as the value. Do this if you need to have more than just a name, like last name, first name, address, etc.
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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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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).
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here is the non-oop way of doing it:
When someone presses a day on a calendar, we need to find out the day, and path. Here is the non-oop way of storing that information:
A string was created with a "-" delimiter between each piece of info we need, like this:
12-c:\files\john_doe.png
Then it was stored in an array. However, to retrieve the data, we then use the "split" function like this.
for (int t = 0;t < day_and_path.length;t++)
{
String[] day_from_db = day_and_path[t].split("-");
String day_db = day_from_db[0];
String path_db = day_from_db[1];
However the OOP way is, make a class with properties: day, path. Then store them into an array of objects.
Which way is better and why?
If you use String#split, you'll be dealing with an array of strings. If all you do is assign the strings to local variables, then there is no point in making a class for that.
If you want to hold on to the string parts and pass them around to other methods, then it begins to make sense to have an object which will conveniently encapsulate those strings.