Desplegar diagonal en una matriz
import java.util.*;
public class diagonal{
public static void main (){
int a[][] = new int [5][5];
int num,i,j;
Scanner teclado = new Scanner (System.in);
System.out.println("Escribe el numero de la diagonal");
num = teclado.nextInt();
for (i=0;i<=4;i++){
for (j=0;j<=4;j++){
if (i==j){
a[i][j]=num;
}
else {
a[i][j]=0;
}
}
}
for (i=0;i<4;i++){
for (j=0;j<4;j++){
System.out.print(a[i][j]+"|");
}
System.out.println("");
}
}
}