Matrix containing numbers and names

I am just learning to program in java, in blueJ, I need to create a code to calculate the salary of workers and in the end print the data of each worker (name, rut, contract, etc) in a matrix, I have been trying to do the matrix to print 4 data, but the blueJ throw me just nullnullnullnull, I do not know what to do to make it work or how I have to do so to print a matrix that has numbers and characters, I leave my code

public class Trabajador

{

public static void getDatos (){
    String rut;
    String nombre ;
    String contrato;
    Scanner leer = new Scanner(System.in);
    System.out.println("Ingrese numeros de trabajadores");
    int j = leer.nextInt();
    String matriz [][] = new String [j][4];
    int y=0;

for(int i=0; i < j; i++){
     System.out.println ("Ingrese nombre del trabajador");
     nombre = leer.next();
     nombre = matriz [i][0];
     System.out.println("Ingrese el rut sin guión");
     rut = leer.next();
     rut = matriz [i][1];
     System.out.println("¿Que tipo de contrato tiene? a.partTime b.Contrato c.Planta");
     contrato = leer.next();
     contrato = matriz [i][2];
    }
for (int x=0; x < matriz.length; x++){
  for(y=0; y < matriz[x].length; y++){
    System.out.print(matriz[x][y]);


  }
     }

} }