I want to merge two arraylists to one new arraylist, and iterate through the list. Before I make actions on my new arraylist, I want to multiple some value times -1. The problem however is, that when using addAll() I also multiple my old arraylist.
public Polynoom subtract (Polynoom that) {
Polynoom subtract = new Polynoom();
subtract.termen.addAll(that.termen);
for (int i = 0; i < subtract.termen.size(); i++) {
subtract.termen.get(i).coef = subtract.termen.get(i).coef * -1;
}
subtract.termen.addAll(this.termen);
Collections.sort(subtract.termen);
subtract.removeDoubles();
return subtract;
}
My Polynoom class looks like this:
class Polynoom implements PolynoomInterface {
ArrayList<Paar> termen = new ArrayList<Paar>();
Polynoom() {
termen = new ArrayList<Paar>();
}
}
The problem is (i think): that when using addAll() it creates REFERENCES instead of new copies, therefore changing the elements will change both. What is nice way to overcome this problem?
I can of course create a new pair instead of a Polynoom an add this pair to a new Polynoom but I don't think that is really nice code. Does someone has a better idea?
try this
subtract.termen = new ArrayList<Paar>(that.termen);
before the loop and remove the subract.termen.addall();
or you can just create new object
ArrayList <Paar> temp = new ArrayList<Paar>(that.termen);
subtract.termen.addAll(temp);
First you can use much nicer methods for iterating :
for (Paar par : substract.termen){
par.coef *= -1;
}
If you want nice approach, your method should look like this :
public Polynoom subtract(Polynoom that) {
Polynoom subtract = this.clone(); //Creates same Polynom, you have to create this method
//Polynoom subtract = new Polynoom(this) => the same as line above using constructor
for (Paar par : that.termen){
substract.sub(par));
}
return subtract;
}
So you have to add function public Paar sub(Paar that)
which substract only one Paar from your polynom. It should be something like this :
public void sub(Paar that){
Paar paar = new Paar(that.coef);
if (this.existsPaarWithSameCoef()){
paar.multipliedBy -= this.findsPaarWithSameCoef().multipliedBy;
} else {
paar.multipliedBy *= -1;
}
return paar;
}
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