https://sas-study.tistory.com/266
https://snupi.tistory.com/54
https://keyboardfoot.tistory.com/160
int[][] arr1 = {{1, 2}, {3, 4}};
int[][] arr2 = Arrays.copyOf(arr1, arr1.length);
int[][] arr3 = Arrays.copyOf(arr1, arr1.length);
arr3[0] = Arrays.copyOf(arr1[0], arr1[0].length);
arr3[1] = Arrays.copyOf(arr1[1], arr1[1].length);
System.out.println(arr1.equals(arr2)); //false
System.out.println(Arrays.equals(arr1, arr2)); //true
System.out.println(Arrays.deepEquals(arr1, arr2)); //true
System.out.println(arr1.equals(arr3)); //false
System.out.println(Arrays.equals(arr1, arr3)); //false
System.out.println(Arrays.deepEquals(arr1, arr3)); //true