jdfinch3 - 14 days ago 5

Java Question

Alternative question: How can I re-use a variable without the value of the first use (that has been added to a list) being changed?

Instead of a long explanation, I'll just post some code, which should explain what I'm trying to do and demonstrate my problem.

`public class Test`

{

static ArrayList<Double> totallist = new ArrayList<Double>();

static ArrayList<Double> inputlist = new ArrayList<Double>();

static ArrayList<ArrayList<Double>> outputlist = new ArrayList<ArrayList<Double>>(); //ArrayList of Arraylists

static double total;

public void test()

{

//the numbers aren't important, just examples

inputlist.add(5);

inputlist.add(3.8);

inputlist.add(1.9);

inputlist.add(.8);

inputlist.add(4.1);

outputlist.get(0).add(9);

outputlist.get(0).add(5.9);

outputlist.get(0).add(4);

outputlist.get(0).add(2.88);

outputlist.get(0).add(5.6);

outputlist.get(1).add(3);

//...etc until outputlist has 5 ArrayLists each with 5 doubles

//I need to multiply each of the 5 inputs by each output in each

//internal ArrayList and then enter the sum of those

//multiplications into totallist

for (int i = 0; i < 5; i++) {

total = 0;

for (int i2 = 0; i2 < 5; i2++) {

double input = inputlist.get(i);

double output = outputlist.get(i).get(i2);

total += input * output;

}

totallist.add(total);

}

}

}

As you can see, the problem is the variable

`total`

`totallist`

I can't figure out a way around this that doesn't involve a huge amount of variables and loops... There has to be something I'm missing.

Answer

There is no problem here to solve. The `total`

variable gets auto-boxed to a `Double`

object before being added to the list. You can reuse `total`

to your heart's content.

However it should certainly be a local variable, not static.