HELP CODING THIS IN JAVA

BUT PLEASE EXPLAIN

DONT USE toCharArray

Given a 1D array of integers A, you are to produce (and return) a 2D array B of integers that is as follows:

B has as many rows as A.length

B has as many columns as A.length

B contains only values 0 except for its diagonal elements: for all elements B[i][i], we have B[i][i] = A[i].

Given a string str, you are to produce (and return) a string, built from str,

* such that all vowels are replaced by a character *.

Given a 1D array of integers A, you are to produce (and return) a 2D array B of positive integers that is as follows:

B has as many rows as A.length

Each ith row of B is of length A[i] and contains only values A[i]

Given a string str, you are to produce (and return) a 1D array S of strings of length = the length of str,

* and where each element S[i] = str.substring(0,i+1).