That’s because Java is not C language.
When you write int arr[][] = {{1, 2, 3, 4}, {4, 3, 2, 1}};, you declare and initialize a multidimensional array of 2 by 4. It is equivalent to the C language initialization you proposed (int arr[2][4] = {{1, 2, 3, 4}, {4, 3, 2, 1}};)

In Java, we preferably declare arrays in a Java-style manner:

int[][] arr = {{1, 2, 3, 4}, {4, 3, 2, 1}};

where int[][] is just a type identifier, we cannot specify size.
Moreover, in Java, we can initialize a 2D array that is not rectangular:

int[][] arr = {{1, 2, 3, 4}, {4, 3}};

If you want to declare an array of specific size, but don’t want to specify all it’s values at once, the only solution is to use new:

int[][] arr = new int[2][4];
arr[0][0] = 1;

Try the following:

int[][] multi = new int[5][10];

... which is a short hand for something like this:

int[][] multi = new int[5][];
multi[0] = new int[10];
multi[1] = new int[10];
multi[2] = new int[10];
multi[3] = new int[10];
multi[4] = new int[10];

Note that every element will be initialized to the default value for int, 0, so the above are also equivalent to:

int[][] multi = new int[][] {
  { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }
};

... or, more succinctly,

int[][] multi = {
  { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
  { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }
};