java 判断一个三阶矩阵是不是单位矩阵

import java.util.Scanner;

class Main {

   public static void main(String[] args) {

      Scanner input = new Scanner(System.in);
      // code here
      int [][] a=new int[3][3];
        for (int i = 0; i <=2; i++) {
            for (int j = 0; j <=2; j++) {
                a[i][j]=input.nextInt();
            }
        }
        if(a[0][0]==a[1][1] && a[1][1]==a[2][2] && (a[0][1])==0 && a[0][2]==0 && a[1][0]==0 && a[1][2]==0 && a[2][0]==0 && a[2][1]==0){
            System.out.println("YES");
        }
        else
            System.out.println("NO");
      input.close();
   }
}