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POUsing ArrayList get(i) to give parameters to create object doesn't work
 

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  1. POUsing ArrayList get(i) to give parameters to create object doesn't work
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    <p>I have this problem. I'm creating a polynomial program, where I can subtract, add and multiply. </p> <p>However I come across this error, I can't really pinpoint, why this happens. </p> <p>First I have my Polynomial.java , I create an arraylist of two inputs, then I sort them based on the exponent, then I loop through this list, if the exponent matches, than a new pair will be created based on adding the coefficients and using the original exponent. </p> <pre><code>public Polynoom subtract(Polynoom that) { Polynoom subtract = new Polynoom(); subtract.termen.addAll(that.termen); for (int i = 0; i &lt; 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; } </code></pre> <p>This will create a list of pairs, with a double and an integer. For example: </p> <pre><code>-1.0 2 -1.0 1 1.0 1 2.0 0 </code></pre> <p>Then I have a method that will look for pair with the same exponent, if so, then it will add the coefficient and takes the exponent of the first pair. </p> <pre><code> private void removeDoubles() { for (int i = 0; i &lt; this.termen.size() - 1; i++) { if (this.termen.get(i).exponent == this.termen.get(i + 1).exponent) { this.termen.set(i, new Pair((this.termen.get(i).coef + this.termen.get(i + 1).coef), (this.termen.get(i).exponent))); this.termen.remove(i + 1); i --; } } } </code></pre> <p>However, somehow the second argument I pass in the new Pair doesn't work. </p> <p>If i for example change the new Pair to: </p> <pre><code>this.termen.set(i, new Pair(13, 2)); result difference: 1.0x^2 + 13.0x^2 + 2.0 (this is correct) </code></pre> <p>If i for example change new Pair to: </p> <pre><code>this.termen.set(i, new Pair(13, this.termen.get(i).exponent); result difference: -1.0x^2 + x^1 + 2.0 (this is not correct) </code></pre> <p>Why if i set the new pair manually, it will work? Why doesn't it work why I use the this.termen.get.exponent? Because I basically do the same: putting an integer when creating a new Pair object. </p> <p>Can anyone give me a tip? :)</p> <p>Thanks!</p> <p>EDIT: </p> <p>My termen class, is part of my Polynomial class, and termen is an custom arraylist of the type pair. </p> <pre><code>class Polynoom implements PolynoomInterface { ArrayList&lt;Paar&gt; termen = new ArrayList&lt;Paar&gt;(); </code></pre> <p>And my pair class: </p> <pre><code>class Paar implements Comparable &lt;Paar&gt; { double coef; int exponent; Paar(double a, int b) { coef = a; exponent = b; } </code></pre> <p>EDIT 2: My toString method of class Polynomial: </p> <pre><code>public String toString() { String temp = ""; for (int i = 0; i &lt; this.termen.size(); i++) { if (i != this.termen.size() - 1) temp += this.termen.get(i) + " + "; else temp += this.termen.get(i); } return temp; } </code></pre> <p>It looks like it keep printing the old list, not the new one. I don't see why exactly. </p>
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    1. PTQuestion
    1. USswennemen
    1. USswennemen
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    1. COCould you post also the class of objects contained by the `Termen? I am interested in the object returned by `termen.get(i)`.
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      1. POUsing ArrayList get(i) to give parameters to create object doesn't work
      1. USherti
    2. COits the Pair class which contains a double (coef) and an int (exponent)
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      1. POUsing ArrayList get(i) to give parameters to create object doesn't work
      1. USPetros Koutsolampros
    3. CO@PetrosKoutsolampros yes, you're right. One more question: `subtract.termen.get(i).coef = subtract.termen.get(i).coef * -1; ` I am not sure I understand what you are doing and I think is missing a paranthesis or something.
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      1. POUsing ArrayList get(i) to give parameters to create object doesn't work
      1. USherti
 

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