Java: class isn't recognized as being an instance of itself

Question

I am trying to implement an associative operator for some matrix operations, and I must also use complex numbers. I encounter the following error after I run my program: java.lang.ArrayStoreException: java.lang.Double , and I found out that this error is because an instanceof check passed as false, when it should be true.

Here is my code:

public void readFromFile(int noOfLines, int noOfColumns,T[][] matrix,T t) throws FileNotFoundException
{
    File file = new File("matrix.txt");
    Scanner s = new Scanner(file);
    for (int i = 0; i < noOfLines; ++i)
    {
        for (int j = 0; j < noOfColumns; ++j)
        {
            if(t instanceof ComplexNumber)
                matrix[i][j] = (T)new ComplexNumber(s.nextInt(), 1);
            else if(t instanceof  Integer)
                matrix[i][j] = (T)new Integer(s.nextInt());
            else
                matrix[i][j] = (T)new Double(s.nextInt());
        }
    }
}

The problem appears at this line

if(t instanceof ComplexNumber)
   matrix[i][j] = (T)new ComplexNumber(s.nextInt(), 1);

and the error at this line

matrix[i][j] = (T)new Double(s.nextInt());

Here is how I call the function

 ComplexNumber[][] matrix1 = new ComplexNumber[noOfLines][noOfColumns];
 file.readFromFile(noOfLines,noOfColumns,matrix1,ComplexNumber.class);

noOfLines and noOfColumns are integers, and readFromFile reads some strings from a file, and it should put them in the matrix1 array. How can I fix the problem, and why isn't ComplexNumber.class (or T t in my readFromFile arguments) and instanceOf ComplexNumber? Thank you.

EDIT: ComplexNumber class

public class ComplexNumber {
public double real;
public double imag;
public String output = "";

public ComplexNumber(double real, double imag) {
    this.real += real;
    this.imag += imag;
}

public ComplexNumber() {
    real = 0;
    imag = 0;
}

public double getReal() {
    return real;
}

public void setReal(double real) {
    this.real = real;
}

public double getImag() {
    return imag;
}

public void setImag(double imag) {
    this.imag = imag;
}

public void add(ComplexNumber num2) {
    this.real += num2.real;
    this.imag += num2.imag;
}

public void subtract(ComplexNumber num) {
    this.real -= num.real;
    this.imag -= num.imag;
}

public void print() {
    System.out.print(real + " " + imag + "i");
}

public String toString() {
    return real + " " + imag + "i";
}
}

Answer 1

You need Class<T> clazz instead of T t as the parameter (or pass in new ComplexNumber instead of ComplexNumber.class ). Then you can replace instanceof with clazz.equals(ComplexNumber.class) (and the same for Integer and Double ).

You're passing in Class<ComplexNumber> and your else clause is picking it up, since it's not a ComplexNumber or an Integer , it's a Class .