Java two-dimensional array basics

Get all elements

Use the length property of the array directly to get the number of array elements in a one-dimensional array. In a two-dimensional array, you can directly use the length property to get the number of rows in the array. Adding length (such as array[0].length) after the specified index indicates how many elements the row has, that is, the number of columns.

If you want to get all the elements in a two-dimensional array, the simplest and most common way is to use the for statement. When outputting all one-dimensional arrays, we use a one-level for loop, while for two-dimensional arrays to output all of them, we use nested for loops (two-level for loops).

class test07 
{
	public static void main(String[] args) 
	{
		double[][] class_score = {
   
   {10.0,99,99},{100,98,97},{100,100,99.5},{99.5,99,98.5}};
		System.out.println("第二行第二列的值：" + class_score[1][1]);
		System.out.println("第四行第一列的值：" + class_score[3][0]);

		//遍历二维数组
		for(int i = 0; i < class_score.length; i++){
			for(int j = 0; j < class_score[i].length; j++){
				System.out.println("class_score[" + i + "][" + j + "] = " + class_score[i][j]);
			}
		}
	}
}

Suppose there is a matrix with 5 rows and 5 columns. The matrix is ​​arranged by numbers within 10 randomly generated by the program. The following uses a two-dimensional array to create the matrix, the code is as follows:

class test08 
{
	public static void main(String[] args) 
	{
		//创建一个二维数组
		int[][] matrix = new int[5][5];
		//随机分配
		for(int i = 0; i < matrix.length; i++){
			for(int j = 0; j < matrix[i].length; j++){
				matrix[i][j] = (int)(Math.random() * 10);
			}
		}
		System.out.println("下面是程序生成的矩阵：");
		//遍历二维数组并输出
		for(int i = 0; i < matrix.length; i++){
			for(int k = 0; k < matrix[i].length; k++){
				System.out.print(matrix[i][k] + " ");
			}
			System.out.println();
		}
	}
}

foreach loop statement output

for(double[] row : class_score){
			for(double val : row){
				System.out.print(val + " ");
			}
			System.out.println();
		}

To quickly print a list of data elements in a two-dimensional array, you can call:

System.out.println(Arrays.deepToString(arrayName));

import java.util.Arrays;
System.out.println(Arrays.deepToString(class_score));