Question

The thing is that I’m trying to print the matrix previously created in the constructor, but seems that it’s empty.

Here’s the code of the constructor:

public Matrix(int row_col){
    int [][] randomMatrix = new int[row_col][row_col];
    Random rand = new Random();
    if (row_col > 0 && row_col < ROW_LIMIT && row_col < COL_LIMIT)
    for (int i = 0; i < randomMatrix.length; i++) 
     for (int j = 0; j < randomMatrix[0].length; j++)
         randomMatrix[i][j] = rand.nextInt(51);
}

And the code of the method print:

public void print(){
    int row = randomMatrix.length;
    int col = randomMatrix[0].length;
    for(int i=0 ; i < row ; i++)
     for(int j=0 ; j < col ; j++)
        System.out.print(randomMatrix[i][j]);
}

Greetings!

Answer 1

Replace

int [][] randomMatrix = new int[row_col][row_col];

by

this.randomMatrix = new int[row_col][row_col];

The constructor initializes and fills a local variable instead of initializing and filling the instance field used by the print() method.