Java dynamic array sizes?

Question

I have a class - xClass, that I want to load into an array of xClass so I the declaration:

xClass mysclass[] = new xClass[10];
myclass[0] = new xClass();
my         


        

Answer 1

Arrays.copyOf() method has many options to fix the problem with Array length increasing dynamically.

Java API

Answer 2

Where you declare the myclass[] array as :

xClass myclass[] = new xClass[10]

, simply pass in as an argument the number of XClass elements you'll need. At that point do you know how many you will need? By declaring the array as having 10 elements, you are not declaring 10 XClass objects, you're simply creating an array with 10 elements of type xClass.

Answer 3

I recommend using vectors instead. Very easy to use and has many predefined methods for implementation.

import java.util.*;

Vector<Integer> v=new Vector<Integer>(5,2);

to add an element simply use:

v.addElement(int);

In the (5,2) the first 5 is the initial size of the vector. If you exceed the initial size,the vector will grow by 2 places. If it exceeds again, then it will again increase by 2 places and so on.

Answer 4

Since ArrayList takes to much memory when I need array of primitive types, I prefer using IntStream.builder() for creating int array (You can also use LongStream and DoubleStream builders).

Example:

Builder builder = IntStream.builder();
int arraySize = new Random().nextInt();
for(int i = 0; i<arraySize; i++ ) {
    builder.add(i);
}
int[] array = builder.build().toArray();

Note: available since Java 8.

Answer 5

Here's a method that doesn't use ArrayList. The user specifies the size and you can add a do-while loop for recursion.

import java.util.Scanner;
    public class Dynamic {
        public static Scanner value;
        public static void main(String[]args){
            value=new Scanner(System.in);
            System.out.println("Enter the number of tests to calculate average\n");
            int limit=value.nextInt();
            int index=0;
            int [] marks=new int[limit];
            float sum,ave;
            sum=0;      
            while(index<limit)
            {
                int test=index+1;
                System.out.println("Enter the marks on test " +test);
                marks[index]=value.nextInt();
                sum+=marks[index];
                index++;
            }
            ave=sum/limit;
            System.out.println("The average is: " + ave);
        }
    }

Answer 6

Yes, wrap it and use the Collections framework.

List l = new ArrayList();
l.add(new xClass());
// do stuff
l.add(new xClass());

Then use List.toArray() when necessary, or just iterate over said List.