How to get the number of rows and columns of a two-dimensional array in JAVA

I am a programming novice, learning programming knowledge from 0.

Let's start with a topic: write a piece of code that prints the contents of a two-dimensional boolean array. Where * means true and space means false. Print row and column numbers.

Code:

public class Ex_11 {

    public static void printBooleans(boolean[][] a){
        
        int rowNum = a.length;
        int colNum=0;
        if(rowNum>0)
            colNum = a[0].length;
        for(int i=0;i<rowNum;i++){
            for(int j=0;j<colNum;j++){
                if(a[i][j])System.out.print("["+i+"]["+j+"]"+"*");
                else System.out.print("["+i+"]["+j+"]"+" ");
            }
            System.out.println();
        }
        
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        
        boolean[][] b = {{true,true,false,false},{false,false,true,true}};
        boolean[][] c={};
        printBooleans(b);
        printBooleans(c);
    }

}

The topic is very simple, new knowledge learned:

1. A two-dimensional array is essentially a one-dimensional array, the number of rows = array name.length, the number of columns = array name[0].length;

2. Number of columns = array name [0].length Before this sentence, it is necessary to judge whether the array is empty. If it is empty, the sub-number represented by the array name [0] does not exist, and an error will be reported.

 

public class Ex_11 {
public static void printBooleans(boolean[][] a){int rowNum = a.length;int colNum=0;if(rowNum>0)colNum = a[0].length;for(int i=0;i<rowNum;i++){for(int j=0;j<colNum;j++){if(a[i][j])System.out.print("["+i+"]["+j+"]"+"*");else System.out.print("["+i+"]["+j+"]"+" ");}System.out.println();}}
public static void main(String[] args) {// TODO Auto-generated method stubboolean[][] b = {{true,true,false,false},{false,false,true,true}};boolean[][] c={};printBooleans(b);printBooleans(c);}
}