How to prevent a variable from going negative in Java?

Question

I’m making an application for Android in Android Studio where there is a list of items, where you can choose to increase or decrease the amount of each item, so for this I created two buttons for each item, one to increase and the other to decrease the amount, follows model:

int quantity_item;

public void increment_item(View view) {
    quantity_item = quantity_item + 1;
    display_item(quantity_item);

}

public void decrement_item(View view) {
    quantity_item = quantity_item - 1;
    display_item(quantity_item);
}

The problem is that when the value is zero and click on the button decrement_item, the value is negative. How do I stop it? How do I stop it when it’s "0", when pressing decrement_item, nothing happens?

Answer 1

Basically create a condition that prevents this:

public void decrement_item(View view) {
    if (quantity_item > 0) {
        quantity_item--;
        display_item(quantity_item);
    }
}

I could also do something like this to better inform:

public void decrementItem(View view) {
    if (quantityItem > 0) {
        quantityItem--;
        displayItem(quantityItem);
    } else {
        messagemErro("Não pode ficar com valor inferior a zero");
    }
}

I put in the Github for future reference.