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POHow can I convert existing procedural code to use classes?
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copied!<p>I'm trying to learn Java and basically my approach has been to take the procedural style I learned with python, and apply it to Java. So I never use classes and just put everything in a single class with many methods(which I just use as python functions). I think I've hit a problem, and need to bite the bullet and use classes, but I'm having trouble wrapping my head around how to do it.</p> <p>To simplify my problem(ignore the poor design- it's just to illustrate the point), I have a program that takes a list and within a for loop does some math on each item(in this case adds 1 to the value of the list). I only want it to do work on 2 items on the list and then stop(in this example it's the first 2 items but in my real program it could be anywhere in the list). Here's the working code that is similar to how I'm already doing it:</p> <p>No Classes:</p> <pre><code>public class LearningClasses { public static void main(String[] args) { int[] list = new int[]{1,2,3,4,5,6,7,8,9,10}; int[] data_list = new int[list.length]; for (int current_location = 0; current_location<list.length;current_location++) { for (int i =0; i<100; i++){ if (check_size(data_list) == false ) { break; } data_list[current_location] = (list[current_location]+1); } } //its done now lets print the results for (Integer item : data_list) { System.out.println(item); } } private static boolean check_size(int[] data_list) { // TODO Auto-generated method stub int count = 0; for (int item : data_list) { if (item != 0) { count++; if (count>=2) { break; } } } if (count>=2) { return false; } else { return true; } } } </code></pre> <p>The problem with this code is although it works it's inefficient because it calculates the count on every iteration of the second for loop. In my program I cannot put anything above the first <code>for loop</code> but I can put anything below it, so I thought instead of doing the count every time maybe I could use a class to somehow maintain state and just increment the number as oppose to recalculating every time.</p> <p>With classes:</p> <pre><code>public class LearningClassesCounter { /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub int[] list = new int[]{1,2,3,4,5,6,7,8,9,10}; int[] data_list = new int[list.length]; for (int current_location = 0; current_location<list.length;current_location++) { //can only put commands in here. Nothing above. Counter checker = new Counter(data_list); System.out.println(checker.check_data()); for (int i =0; i<100; i++){ data_list[current_location] = (list[current_location]+1); } } //its done now lets print the results for (Integer item : data_list) { System.out.println(item); } } } class Counter { private int count; // current value private boolean continue_or_not; private int[] data_list; // create a new counter with the given parameters public Counter(int[] data_list) { data_list = this.data_list; count = 0; continue_or_not = true; } public boolean check_data() { // TODO Auto-generated method stub int count = 0; for (int item : data_list) { if (item != 0) { count++; if (count>=3) { break; } } } if (count>=3) { return false; } else { return true; } } // increment the counter by 1 public void increment() { count++; } // return the current count public int value() { return count; } } </code></pre> <p>This doesn't work because it thinks the data_list is a null pointer(I know I'm declaring it null, but if I make it private int[] data_list = data_list it doesn't compile either). My ultimate goal is to have some kind of controls, in this case its limiting it to 2 items but I want to also add other limits like total value of al items cannot exceed X or cannot be lower than X and want to save CPU power by not having to do full calculations every time. So I think I need to be able to increment the values and then need to check that those increments haven't exceeded thresholds. </p> <p>Can anyone help me understand what I'm doing wrong? Am I only wrong with syntax; or am I designing this wrong?</p>

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