Java/2D array

1. Two-dimensional array:
   1. Format definition: (1) Data type [] [] array name = new data type [m][n] ; (commonly used) eg: int[][] arr=new int[m] [n];
           m: represents how many one-dimensional numbers are in the current two-dimensional array
           n: represents the length of each one-dimensional array
      (2) data type [] array name [] = new data type [m][n]
      (3) data type array name [][] = new data type [m][n] 
              (4) data type [][] array name = new data type [m][] ; (commonly used)

                   Only m one-dimensional arrays are given, the length of each one-dimensional array is dynamically given, and then the length of each one-dimensional array is dynamically given.

              (5) Static initialization (commonly used)

     datatype[][] array name = {{element1,element2,element3},{....}};

2. Traversal of two-dimensional arrays

public class ArrayTest {
	
	public static void main(String[] args) {
		//Define a two-dimensional array, static initialization
		int[][] arr = {{1,2,3},{4,5,6},{7,8,9}};
		
		for(int x = 0 ; x < arr[0].length ; x ++) {
			System.out.println(arr[0][x]);
		}
		System.out.println("---------------------");
		
		for(int x = 0 ; x < arr[1].length ; x ++) {
			System.out.println(arr[1][x]);
		}
		System.out.println("---------------------");
		
		for(int x = 0 ; x < arr[2].length ; x ++) {
			System.out.println(arr[2][x]);
		}
		
		System.out.println("----------------------------");
		//Improvement: through the outer loop, arr.length: the outer loop is the length of the two-dimensional array
		for(int x = 0 ; x < arr.length ; x ++) {
			for(int y = 0 ; y < arr[x].length; y++) {
				System.out.print(arr[x][y]+" ");
			}
		}
		System.out.println("----------------------------");
		//Final code: define a function that traverses a two-dimensional array
		printArray2(arr);
	}
	
	public static void printArray2(int[][] arr) {
		for(int x = 0 ; x < arr.length ; x ++) {
			for(int y = 0 ; y < arr[x].length ; y++) {
				System.err.print(arr[x][y]+" ");
			}
		}
	}
}

3. Summation of two-dimensional arrays

Fourth, the sorting of two-dimensional array