How to test my program from the main method JAVA

I am new in Java. I would like to test this calculator in the main method. What is the most efficient way you could test this?

package BeginnerLevel;

import java.util.Scanner;

public class Calculator {

This is the constructor:

public Calculator(){


  while (true){
      System.out.println("Personal Calculator\n"+
      "Addition---> 1 \n"+"Subtraction---> 2\n"+"Multiplication---> 3\n"+"Division---> 4\n"+"Exit--->0");
       Scanner input = new Scanner(System.in);

       int UsrIn= input.nextInt();

       input.close();


      switch (UsrIn){

      case 1: 
          Addition();
          break;
      case 2: 
          Subtraction();
          break;
      case 3:
          Multiplication();
          break;

      case 4:
          Division();
          break;

      case 0:
          break;  
      }


  }
}

These are the methods that are called in the switch case.

Addition method:

private void Addition(){

     Scanner input= new Scanner(System.in);

     double total=0;
     double firstnum=0;
     double secondnum=0;

     System.out.println("Enter Fist number: ");
     firstnum= input.nextDouble();

     System.out.println("Enter Fist number: ");
     secondnum=input.nextDouble();
    input.close();

     total= firstnum + secondnum;

    System.out.println("The result of Addition for "+ firstnum +" + "+secondnum+" is "+total);
}

Subtraction method:

private void Subtraction(){

    Scanner input= new Scanner(System.in);

    double total=0;
    double first=0;
    double second=0;

    System.out.println("Enter First number ");
    first=input.nextDouble();

    System.out.println("Enter Second number ");
    second=input.nextDouble();

    total= first-second;
    System.out.println("The result of Addition for "+ first +" + "+second+" is "+total);

    input.close();

}

Multiplication method:

private void Multiplication(){
Scanner input= new Scanner(System.in);

    double total=0;
    double first=0;
    double second=0;

    System.out.println("Enter First number ");
    first=input.nextDouble();

    System.out.println("Enter Second number ");
    second=input.nextDouble();

    total= first*second;
    System.out.println("The result of Addition for "+ first +" + "+second+" is "+total);

    input.close();
}

Division Method:

private void Division(){
    Scanner input= new Scanner(System.in);
    double total=0;
    double first=0;
    double second=0;

    System.out.println("Enter First number ");

    first=input.nextDouble();

    System.out.println("Enter Second number ");
    second=input.nextDouble();

    total= first*second;
    System.out.println("The result of Addition for "+ first +" + "+second+" is "+total);

    input.close();

} 

}

Any recommendation is appreciated !