How to create a 2D double array with column of ones

I am in need of computing column sums in java using apache's RealMatrix. This would work like this:

import org.apache.commons.math3.linear.RealMatrix;
import org.apache.commons.math3.linear.MatrixUtils;

double[][] values = {{1.0, 2.0}, {3.0, 4.0}, {5.0, 6.0}};
RealMatrix matrix = MatrixUtils.createRealMatrix(values);

MatrixUtils.createRealMatrix(new double[][]{{1, 1, 1}}).multiply(matrix)
>> Array2DRowRealMatrix{{9.0,12.0}}

However, I would like to make it general when it comes to declaring ones in

MatrixUtils.createRealMatrix(new double[][]{{1, 1, 1}})

Is there a way to pre-declare the number of ones I want inside a curly bracket?

Say I want numberOfOnes = 10, then:

MatrixUtils.createRealMatrix(new double[][]{{1, 1, 1, 1, 1, 1, 1, 1, 1, 1}})

I am struggling to find a way to make this general. Any help?

You can use Arrays.fill:

double[][] m = new double[rows][cols];
for (int i = 0; i < rows; i++)
    Arrays.fill(m[i], 1.0);

You can use Arrays.setAll method to process each row separately:

double[][] m = new double[rows][];
Arrays.setAll(m, i -> {
    double[] row = new double[cols];
    Arrays.fill(row, 1.0);
    return row;
});