This is version 1 of matrix multiplication program. It doesn't work. Why?

public class MatrixMultiplication {
	public static void main (String [] args){
	
	int [] [] a = {{4, 5, 6}, {1, 0, 2}};
	int [] [] b = {{7,1}, {0,1}, {1,2}};
	int [] [] c = new int[b.length] [a[0].length];
	
	if(b.length != a[0].length){
		System.out.println("These matrices cannot be multiplied");
		return;
	}
	for (int i = 0; i < a.length; i++){
		int sum = 0;
		int j = 0;
		for (j = 0; j < a[0].length; j++){
			sum += a[i][j] * b[j][i];
		}
		c[i][j] = sum;
	}
	
	}
}

This is an example from CSci 1211 course.

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