Chapter 8.2, Problem 8.2.4CP

Which of the following statements are valid?

int [] [] r = new int[2];

int [] x = new int[];

int [] [] y = new int[3] [];

int [] [] z = {{1, 2}};

int [] [] m = {{1, 2}, {2, 3}};

int [] [] n = {{1, 2}, {2, 3},} ;