"Cannot find symbol" when testing Java code

Question

I've started writing a class to model a matrix and the compiler gives me this message:

Matrix.java:4: cannot find symbol
symbol  : constructor Matrix(int[][])
location: class Matrix
  Matrix y = new Matrix(x);

This is the code that I was trying to compile:

public class Matrix<E> {
    public static void main(String[] args) {
        int[][] x = {{1, 2, 3}, {1, 2, 3}, {1, 2, 3}, {1, 2, 3}};
        Matrix y = new Matrix(x);
        System.out.println(y.getRows());
        System.out.println(y.getColumns());
    } 
    private E[][] matrix;
    public Matrix(E[][] matrix) {this.matrix = matrix;}
    public E[][] getMatrix() {return matrix;}
    public int getRows(){return matrix.length;}
    public int getColumns(){return matrix[0].length;}
}

So, my question is, why am I getting this error, and what should I change to fix this?

duffymo · Accepted Answer · 2010-07-24T22:54:24.257

Try it like this:

public class Matrix<E> {
    public static void main(String[] args) {
        Integer [][] x = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}, {0, 1, 0}};
        Matrix<Integer> y = new Matrix<Integer>(x);
        System.out.println(y.getRows());
        System.out.println(y.getColumns());

        System.out.println("before: " + y);
        Integer [][] values = y.getMatrix();
        values[0][0] = 10000;
        System.out.println("after : " + y);
    }
    private E[][] matrix;
    public Matrix(E[][] matrix) {this.matrix = matrix;}
    public E[][] getMatrix() {return matrix;}
    public int getRows(){return matrix.length;}
    public int getColumns(){return matrix[0].length;}
    public String toString()
    {
        StringBuilder builder = new StringBuilder(1024);
        String newline = System.getProperty("line.separator");

        builder.append('[');
        for (E [] row : matrix)
        {
            builder.append('{');
            for (E value : row)
            {
                builder.append(value).append(' ');
            }
            builder.append('}').append(newline);
        }
        builder.append(']');

        return builder.toString();
    }
}

Compiles and runs on my machine.

You need to think about something else: encapsulation and when "private" isn't private. Check out the modification to the code and see how I'm able to modify your "private" matrix.

Thanks, compiles and runs on my machine too. Guess I should have read up a bit more on syntax for generics before I got started with them — Rafe Kettler, Jul 24 '10 at 22:44
SO has a time limit for how quickly you can accept an answer. I tried a little ago, but I'll have to wait a little while to accept (unless someone else comes up with a super amazing answer that proves the existence of the god particle or something crazy like that) — Rafe Kettler, Jul 24 '10 at 22:50

score 1 · Answer 2 · answered Jul 24 '10 at 22:37

1

Try using Integer[][] instead of int[][]. Your constructor expects the former (since there are no primitive type arguments), and you are passing the latter.

answered Jul 24 '10 at 22:37

Bozho

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Why is this upvoted? The real problem is the generic part of the type declaration is missing. This answer misses the mark. – Erick Robertson Jul 24 '10 at 22:48

score -2 · Answer 3 · edited May 23 '17 at 12:30

-2

There is no generic array creation in Java. See How to create a generic array in Java?

edited May 23 '17 at 12:30

Community

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answered Jul 24 '10 at 22:36

Sasi

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This doesn't really pertain to what I'm doing with this class. – Rafe Kettler Jul 24 '10 at 22:46

"Cannot find symbol" when testing Java code

3 Answers3