How can I make a resizable array in Java?

Question

What is the best way to do a resizable array in Java? I tried using Vector, but that shifts all elements over by when when you do an insert, and I need an array that can grow but the elements stay in place. I'm sure there's a simple answer for this, but I still not quite sure.

Answer 1

An array cannot be resized dynamically in Java. The solution to this is using ArrayList or creating another temporary array and then assign it.

You can find tutorials about ArrayList, but if you just want custom ResizableArray in Java. Here's it is. But it's NOT recommend to use! It's just a FAKE resizable array and heap memory will be increased when you create too many objects. This is just to show you the idea.

• The Interface

public interface Resizable<T> {

    void add(T data);
    int delete(int index);
    int size();
    void print();
}

• Implementation Class

public class ResizeableImpl<T> implements Resizable<T> {

    private Object[] temp = null;
    private Object[] originals = new Object[0];

    @Override
    public void add(T data) {
        Object[] temp = new Object[originals.length+1];
        for (int i=0; i<originals.length; i++) {
            temp[i]=originals[i];
        }
        temp[originals.length]=data;
        originals=temp;
    }

    @Override
    public int delete(int index) {
        int success=0;
        switch (originals.length) {
            case 0: //No Data to delete
                success=0;
                break;
            case 1: //One Data is delete and so no data, too!
                originals = new Object[0];
                success = 1;
                break;
            default: //>=2
                int count=0;
                originals[index]=null;
                temp = new Object[originals.length-1];
                for (int i=0; i<originals.length; i++) {
                    if (originals[i]!=null)
                    temp[count++]=originals[i];
                }
                originals = temp;
                success = 1;
        }

        return success;
    }

    @Override
    public int size() {
        return originals.length;
    }

    @Override
    public void print() {
        StringBuilder sb = null;

        if (originals.length==0) {
            System.out.println("No data available!");
            return;
        }

        for (int i=0; i<originals.length; i++) {
            if (sb==null) {
                sb = new StringBuilder();
                sb.append(originals[i]);
            }
            else {
                sb.append(", "+originals[i]);
            }
        }
        sb.append(".");
        System.out.println(sb.toString());
    }
}

• Main method

public class App {

    public static void main(String[] args) {
        //Program to interfaces, not implementations
        Resizable<Integer> obj = new ResizeableImpl<>();

        obj.add(13);
        obj.add(20);
        obj.add(17);
        obj.add(25);
        obj.add(100);
        obj.add(12);
        obj.print();

        int result = obj.delete(2); //This will delete 17.
        if (result==1) {
            System.out.println("Deletion is successful!");
        }
        obj.print();

        obj.delete(3); //This will delete 100.
        obj.print();
    }
}

Output

13, 20, 17, 25, 100, 12.
Deletion is successful!
13, 20, 25, 100, 12.
13, 20, 25, 12.