I want to undrestan how i can use switch?

package expnum;
import java.util.Scanner;
public class Main {

    public static void main(String[] args) {
     Scanner input = new Scanner(System.in);
     int numbers[];
     int number;
    int word;
     String expression[]={"+" , "-" , "*" , "/"};
     System.out.println("please enter 3 numbers:");
     number=input.nextInt();
     System.out.println("please enter 2 expression (+ , - ,* , /):");
      word = input.nextInt();
  //   public void answer(int expression){}
      class answer 
{
    // public static void answer (String[]args)
    {
        int expression=5;
        switch(expression)
        {
            case 1:  System.out.println(" + ");break;
            case 2:  System.out.println(" - ");break;
            case 3:  System.out.println(" * ");break;
            case 4:  System.out.println(" / ");break;
            default: System.out.println("in valid");break;
    }
}
}

     {
     }
}