Java Basic Object Program

Question

I don't understand why it doesn't give a random amount. Please explain.

Thanks :)

my code(learned from tutorial):

public class day5 {
    int totalwater = 0;

    public day5(){
        //default constructor
    }
    public day5(int wateramount){
        totalwater = wateramount;
    }
    // don't need static in Object. It will be used in other classes.
    public void addwater(int amount){
        totalwater = totalwater + amount;
    }
    public void drinkwater(int amount){
        totalwater = totalwater - amount;
    }
    public int getwater(){
        return totalwater;
        //because we are going to return an integer, public "int" and "return"
    }
}



public class day5obtest {
    public static void main(String[] args){
        day5 waterbottle = new day5(0);
        int rand = (int)(Math.random()*100);
        waterbottle.addwater(rand); 
        waterbottle.drinkwater(rand);
        System.out.println("The amount of water in your bottle now is: " + waterbottle.getwater());
    }
}

Output:

The amount of water in your bottle now is: 0

Are you expecting the amount of water to have changed after calling drinkwater() ? — SamTebbs33
– SamTebbs33, Commented May 9, 2015 at 22:57

Tamas G. · Accepted Answer · 2015-05-09 22:58:37Z

5

You add and drink the same amount. You have to generate a new random amount after adding, like this:

    int rand = (int)(Math.random()*100);
    waterbottle.addwater(rand); 
    rand = (int)(Math.random()*100);
    waterbottle.drinkwater(rand);

answered May 9, 2015 at 22:58

Tamas G.

7474 gold badges21 silver badges40 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Jay da science noob Over a year ago

Oh! I understand now! Thanks very much. I feel dumb xD

The Coding Wombat · Accepted Answer · 2015-05-09 22:59:28Z

1

You only generate one random number.

You add a randomly generated number to the amount of water, but then you remove that same number from the amount of water, so there's always a net change of 0.

To fix this you could create a second random number rand2 and remove that from the amount of water in drinkwater()

answered May 9, 2015 at 22:59

The Coding Wombat

8151 gold badge11 silver badges34 bronze badges

Comments

MChaker · Accepted Answer · 2015-05-09 23:12:54Z

1

It is a good practice to begin you class name with uppercase like Day5.
Add getters and setters in your Day5 class therefore you can access their fields outside.
If you want to make your program more realistic, add a test in your drinkwater method

as follow

public void drinkwater(int amount){
    if(amount<=totalwater)
        totalwater = totalwater - amount;
    else 
        System.out.println("amount bigger than total water");
}

Make new random amount after adding water.

Finally

 int rand = (int)(Math.random()*100);
 waterbottle.addwater(rand); 
 rand = (int)(Math.random()*100);
 waterbottle.drinkwater(rand);

edited May 9, 2015 at 23:12

answered May 9, 2015 at 23:02

MChaker

2,6572 gold badges24 silver badges38 bronze badges

2 Comments

Tamas G. Over a year ago

You have a point there, this way negative result can be avoided.

MChaker Over a year ago

it is logic that we cannot drink more than we have ;) @TamásG.

Collectives™ on Stack Overflow

Java Basic Object Program

3 Answers 3

1 Comment

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related