Create object in java with arrays

Question

ok so lets say I got class Bulb and class Picture. In bulb I got boolean variable if it is true the bulb is on if not the bulb is off I made it in the constructor that is off by default and made 2 method turnOn and turnOff. I need to make in picture arrays of Bulbs the user enter (in the main method when he creates the object picture) the length of the array . so lets say this is my picture class :

private Bulb [] arr ;

Picture(int len)
{   
    Bulb [] arr = new Bulb[len];
}

Now if I want to enter bulb on each cell I need to do this :

Bulb b = new Bulb();
Bulb c = new Bulb();
Bulb d = new Bulb();

for(int i=0;i<len;i++)
{
    arr[i] = b;
    arr[i] = c;
    arr[i] = d;
}

Of course I can't do this in that way I don't now how many object to create its by the variable len .

You're currently overwriting each assignment you do to arr[i]. — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Nov 26, 2013 at 22:30
Why not for(int i = 0; i < len; i++) { arr[i] = new Bulb(); } ? — Raul Rene
– Raul Rene, Commented Nov 26, 2013 at 22:33

kviiri · Accepted Answer · 2013-11-26 22:33:22Z

2

You can use the length attribute of an array to fill an array with bulbs.

for(int i = 0; i < arr.length; i++) {
    arr[i] = new Bulb();
}

answered Nov 26, 2013 at 22:33

kviiri

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Comments

Andrei Nicusan · Accepted Answer · 2013-11-26 22:33:39Z

1

You don't have to create all Bulb instances before the loop, because you simply don't know how many you need. Why don't you try something simple like the below?

private Bulb [] arr ;

Picture(int len)
{   
    arr = new Bulb[len];
    for(int i=0;i<len;i++)
    {
        arr[i] = new Bulb();
    }
}

answered Nov 26, 2013 at 22:33

Andrei Nicusan

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Comments

JC. · Accepted Answer · 2013-11-26 22:37:59Z

0

I think you would want an ArrayList, which is an resizable array implementation of the List.

...
ArrayList<Bulb> bulbs = new ArrayList<Bulb>();
for(Class cell:cells) {
bulbs.add(new Bulb());
}
...

-OR-

If you really want number related indices to pull the bulb back later:

...
HashMap<int,Bulb> bulbs = new HashMap<int,bulb>();
for(int i=0,i<len;i++) {
bulbs.put(i,new Bulb);
}
...

answered Nov 26, 2013 at 22:37

JC.

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Comments

k2col · Accepted Answer · 2013-11-26 22:38:29Z

0

There are a couple of problems with your code:

Your constructor creates a new variable rather than instantiating the field
Your for loop writes each bulb to the same index. You will end up with an array of 'd' bulbs

It might be easier to use a List if you need to access your Bulbs by index, or a Set if you don't.

private List<Bulb> bulbs;

Picture(int len)
{   
    bulbs = new ArrayList<Bulb>()
}

and then

Bulb b = new Bulb();
Bulb c = new Bulb();
Bulb d = new Bulb();

bulbs.add(b);
bulbs.add(c);
bulbs.add(d);

Then, for example to get bulb B:

bulbs.get(1);

answered Nov 26, 2013 at 22:38

k2col

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