Variable length array

Question

I just started learning java and wrote this variable length array as my first program. I wanted people's opinion on how "java" this code is. For example coding conventions, idioms that I could have used or any improvements that could be made.

MyClass.java:

package myproject;

public class MyClass {

    public static void main(String[] args) {        
        MyArray array = new MyArray();
        
        for (int i = 0; i < 100; i++) array.Push(i);
        
        for (int i = 0; i < array.Size(); i++) {
            System.out.println(array.Get()[i]);
        }

    }
}

MyArray.java:

package myproject;

public class MyArray {
    public MyArray() {
        array = new int[size];
    }
    
    public MyArray(int size) {
        this.size = size;
        array = new int[size];
    }
    
    public int[] Get() {
        return array;
    }
    
    public void Push(int number) {
        if (currentIndex >= size) {
            IncreaseArraySize();
        }
        array[currentIndex] = number;
        currentIndex++;
    }
    
    int Size() {
        return currentIndex;
    }
    
    private void IncreaseArraySize(){
        if (size == 0){
            size++;
        }
        else {
            size *= 2; 
        }
        
        int newArray[] = new int[size];
        for (int i = 0; i < array.length; i++) {
            newArray[i] = array[i];
        }
        array = newArray;
    }
    
    private int size = 0;
    private int currentIndex = 0;
    private int[] array;
}

I was also kind of sceptical of this line : array = newArray; at first but the program seems to work fine.

Answer 1

Advice 1

public MyArray() {
    array = new int[size];
}

Above, size is 0, so you are allocating a zero-length array. Useless. Consider this:

private static final int INITIAL_CAPACITY = 10; // Or some other reasonable constant but 10.

public MyArray() {
    array = new int[INITIAL_CAPACITY];
}

Advice 2

    ...
    private int size = 0;
    private int currentIndex = 0;
    private int[] array;
}

You put your fields after everything else. The conventional portion of a Java file for fields is right after static constants and right before constructors:

private static final int INITIAL_CAPACITY = 10;

private int size = 0;
private int currentIndex = 0;
private int[] array;

public MyArray() {
    ...
}

Advice 3

Once again, the fields:

private int size = 0;
private int currentIndex = 0;
private int[] array;

JVM sets int fields to zero by default. Consider this:

private int size;
private int currentIndex;
private int[] array;

Advice 4

public int[] Get() {
    return array;
}

Wrong. Please, don't expose data structure related internals to the outside world.

Advice 5

Method names must come in camelCase, not in PascalCase.

Advice 6

public MyArray(int size) {
    this.size = size;
    array = new int[size];
}

What?! Your MyArray (no pun intended) is of size of size at the very beginning? In the state where all the "elements" are 0?

Advice 7 (ignore)

Actually, it seems to me that you don't need to keep size at all. Judging from your implementation we have always size == array.length. Ditch the size and rely on array.length; much easier to follow.

Advice 8

I suggest you add a get(int) method for accessing the data.

Advice 9

In IncreaseArraySize(), you could use System.arraycopy. Most likely, it will copy faster on large arrays.

Answer 2

    private int size = 0;
    private int currentIndex = 0;

Given how you use these, better names would be

    private int capacity = 0;
    private int size = 0;

But as @coderodde already noted, it would make more sense to get the capacity from array.length rather than maintain it separately.

I would also rename array to data, but that's a more arguable point.