CODEWITHSUNDEEP
javafor-looparraylist
user4607619
user4607619

Reputation:

Is there a more efficient way to create new variables in a for loop?

If you have an ArrayList (named al in this case), and you're looking to get the first five elements of the list as variables, you could do this:

    String x1 = al.get(0);
    String x2 = al.get(1);
    String x3 = al.get(2);
    String x4 = al.get(3);
    String x5 = al.get(4);

However, using a for loop, is there a way you could do something like this instead:

for (int i = 1; i < 6; i++){
    String namer = "x" + i.toString();
    String [value of String 'namer'] = al.get(i-1);
}

Or is there a completely different method that is much more efficient?

Upvotes: 4

Views: 150

Answers (5)

konkked
konkked

Reputation: 3231

If you are trying to literally create variables on the local stack dynamically you would need to use reflection both ways (if it is even possible, which I don't think it is), otherwise it wouldn't compile then I would stick with the rule of thumb of Don't optimize unless you need to

If you are trying to create a reference to variables you can use a map

Map variables = new HashMap();
for (int i = 1; i < 6; i++) {
    variables.put("x"+i, al.get(i-1));
}

Then you can access like this

variables.get("x1"); //or x2,x3,x4

Upvotes: 2

Drux
Drux

Reputation: 12678

"Perhaps" you don't want to do this in practice, but you could (all from within your program):

  1. write the boxed source code (String x1 = ...) as a proper class to a *.java file (with adjustments as needed)
  2. run the Java compiler to derive a corresponding *.class file
  3. class-load the class from that *.class file into your program and use it

Upvotes: 1

Prikso NAI
Prikso NAI

Reputation: 2652

Dynamic metaprogramming is not possible in java. Depending on what you are trying to achieve, there would be various options.

If you are trying to work in batches of 5 items, the cleanest solution is the one you are using now. If code duplication bothers you as much as it bothers me, then you are looking into Views in Java Collections Framework, specifically the "View of a portion of a collection" section:

List<String> nextFive = list.subList(5, 10);

Upvotes: 5

James Taylor
James Taylor

Reputation: 6268

Why don't you just iterate through the ArrayList and break when you have reach the correct number of variables?

int i = 0;
for (Object obj : al) {
    if (i > 5) { break; }
    results.append(obj); // append the first five elements to the result
}

This, to my knowledge, is the quickest way to do it, since I believe the get() method is O(n). So expliciting writing a get() would prompt n! calls for the first n objects.

Upvotes: 1

HelloWorld
HelloWorld

Reputation: 1103

You can have a String array of size 6 and do the following:

String[] str = new String[6];
for(int i=0; i<str.length; i++)
    a[i] = al.get(i);

Upvotes: 3

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