Q:

How to create a copy and return its object without using clone?

i was wondering how to create a copy and return its object without using the clone function.
    public double[] Mean(double[][] data) {

    double[] x = data[0].clone();

A:

You can use this:
double copy = Arrays.copyOf(data[0],data[0].length);

Which will, as the name states, return a copy of the array. 
NOTE: this will only work for arrays, since it's a method from java.util.Arrays (self-explanatory) 

A:

public double[] colMean(double[][] data) {
    double[] x = new double[data[0].length];
    for (int i = 0; i < x.length; i++) {
        x[i] = data[0][i];
    }
    return x;
}

Odd that you only want to copy data[0] though, but whatever...

