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Creating a Dynamic Array in Java

  • Last Updated : 30 Jun, 2021

Arrays are linear data structures which means that similar types of elements will be inserted as known in a continuous manner. Now as we know there is an issue with arrays that size needs to be specified at the time of declaration or taken from the user in java which constricts ourselves. Hence, there arise dynamic arrays in java in which entries can be added as the array increases its size as it is full. The size of the new array increases to double the size of the original array. Now all elements are retained in a new array which is in specified array domain size and the rest are added after them in the newly formed array. This array keeps on growing dynamically. 

Procedure: 

  1. First, we declared an array of types int with the private access specifier.
  2. Declare the count variable.
  3. Create a constructor that initializes the array of the given length.
  4. Here the magic comes with the method insert.
  5. First, before we insert the value it checks for the length of the array and count variable if both are of the same size then the array is said to be full.
  6. Then we create a new array whose size is twice the size of the previous array.
  7. Just initialized the new array with the previous array and reinitialized it back to the previous array.

Implementation: Creating an Array class that declares the int arr and int count. We just created an array whenever the array is full the array will be resized. 

Example

Java




// Java Program to Create a Dynamic Array
 
// Class 1
// Helper class
class Array {
 
    // Member variables of this class
    // Private access modifier
    private int arr[];
    private int count;
 
    // Note they can only be called through function
 
    // Method 1
    // Inside helper class
    // to compute length of an array
    public Array(int length) { arr = new int[length]; }
 
    // Method 2
    // Inside helper class
    // To print array
    public void printArray()
    {
 
        // Iterating over array using for loop
        for (int i = 0; i < count; i++) {
 
            // Print the elements of an array
            System.out.print(arr[i] + " ");
        }
    }
 
    // Method 3
    // Inside Helper class
    public void insert(int element)
    {
 
        if (arr.length == count) {
 
            // Creating a new array double the size
            // of array declared above
            int newArr[] = new int[2 * count];
 
            // Iterating over new array using for loop
            for (int i = 0; i < count; i++) {
                newArr[i] = arr[i];
            }
 
            // Assigning new array to original array
            // created above
            arr = newArr;
        }
 
        arr[count++] = element;
    }
}
 
// Class 2
// Main class
public class GFG {
 
    // Main driver method
    public static void main(String[] args)
    {
 
        // Creating object of Array(user-defined) class
        Array numbers = new Array(3);
 
        // Adding elements more than size specified above
        // to the array to illustrate dynamic nature
        // using the insert() method
 
        // Custom input elements
        numbers.insert(10);
        numbers.insert(30);
        numbers.insert(40);
        numbers.insert(50);
 
        // Calling the printArray() method to print
        // new array been dynamically created
        numbers.printArray();
    }
}
Output
10 30 40 50 

 

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