java计算器中的用户定义方法

public static void main(String[]args) {
           @SuppressWarnings("resource")
           Scanner input = new Scanner(System.in);
           double num1,num2,add,num3,difference,multiply,divide,square,cube;
           double power,sqrt,cbrt;
           double sin,cos,tan,abs,log,reciprocal,round,percentage;

           int op;


       System.out.println("MENU");     
       System.out.println(" Arithmetic/Power        Power/Roots         Tangent                  Rounding Off      Miscellaneous ");    
       System.out.println("1. Addition             5. Square            10. Sine            13. Round       16. Percent % ");   
       System.out.println("2. Subtraction          6. Cube       11. Cosine            14. Ceil           17. Absolute ");
       System.out.println("3. Multiplication    7. Power         12. Tanget          15. Floor      18. Log ");
       System.out.println("4. Division          8. Square root  \t                              19. Reciprocal");
       System.out.println("                        9. Cube Root ");
       System.out.println("     ");

      System.out.println(" Press 0 to Exit ");

    while (true ){
        System.out.println("select one option" );
        op =input.nextInt();
    switch (op) {
    case 1:
        System.out.println("enter num1: ");
        num1=input.nextDouble();
        System.out.println("enter num2: ");
        num2=input.nextDouble();
        return add(num1,num2);
        break;
    case 2:
        System.out.println("enter num1: ");
        num1=input.nextDouble();
        System.out.println("enter num2: ");
        num2=input.nextDouble();
        return subtract(num1,num2);
        break;
    case 3:
        System.out.println("enter num1: ");
        num1=input.nextDouble();
        System.out.println("enter num2: ");
        num2=input.nextDouble();
        return multiply(num1,num2);
        break;
    case 4:
        System.out.println("enter num1: ");
        num1=input.nextDouble();
        System.out.println("enter num2: ");
        num2=input.nextDouble();
        return divide(num1,num2);
        break;
    case 5:
     System.out.println("enter num1: ");
    num1=input.nextDouble();
    return square(num1);
    break;

    case 6: 
        System.out.println("enter num1: ");
     num1=input.nextDouble();
    return cube(num1);
    break;

    case 7:
     System.out.println("enter first num: " );
     num1=input.nextDouble();
        System.out.println("enter second num: " );
        num2=input.nextDouble();
      return power(num1,num2);

    case 8:
     System.out.println("enter num1: ");
     num1=input.nextDouble();
    return sqrt(num1);
    break;

    case 9:
     System.out.println("enter num1: ");
     num1=input.nextDouble();
      return cbrt(num1);
       break; 

    case 10:
     System.out.println("enter num1: ");
     num1=input.nextDouble();
      return sin(num1);
      break;

    case 11:
     System.out.println("enter num1: ");
     num1=input.nextDouble();
      return cos(num1);
      break;


    case 12:
     System.out.println("enter num1: ");
     num1=input.nextDouble();
      return tan(num1);
      break;

    case 13:
     System.out.println("enter num1: ");
     num1=input.nextDouble();
      return round(num1);
      break;

    case 14:
     System.out.println("enter num1: ");
     num2=input.nextDouble();
     return ceil(num1); 
     break;

    case 15:
      System.out.println("enter num1: ");
     num1=input.nextDouble();
      return floor(num1);
      break;

    case 16:
     System.out.println("enter first num: " );
        num1=input.nextDouble();
        System.out.println("enter second num: " );
     num2=input.nextDouble();
     return percentage(num1,num2);
        break;

    case 17:
     System.out.println("enter num1: " );
        num1=input.nextDouble();
     return abs(num1);
     break;

    case 18:
     System.out.println("enter num1: " );
        num1=input.nextDouble();
     return log(num1);
         break;
    case 19:
     System.out.println("enter num1: " );
        num1=input.nextDouble();
     return reciprocal;
        break;
    } 
    }

    public static double add(num1,num2){
        return num1+num2;
    }
    public static double subtract(num1,num2) {
        return num1-num2;
    }
    public static double multiply(num1,num2) {
        return num1*num2;
    }
    public static double divide(num1,num2) {
        return num1/num2;
    }
    public static double square(num1) {
        return num1*num1;
    }
    public static double cube(num1) {
        return num1*num1*num1;
    }
    public static double power(num1,num2) {
        return Math.pow(num1, num2);
    }
    public static double sqrt(num1) {
        return Math.sqrt(num1);
    }
    public static double cbrt(num1) {
        return Math.cbrt;
    }
    public static double sin(num1) {
        return Math.sin(num1);
    }
    public static double cos(num1) {
        return Math.cos(num1);
    }
    public static double tan(num1) {
        return Math.tan(num1);
    }
    public static double round(num1) {
        return Math.round(num1);
    }
    public static double ceil(num1) {
        return Math.ceil(num1);
    }
    public static double floor(num1) {
        return Math.floor(num1);
    }
    public static double percentage(num1,num2) {
        return (num1*100/num2);
    }
    public static double abs(num1) {
        return Math.abs(num1);
    }
    public static double log(num1) {
        return Math.log10(num1);
    }
    public static double reciprocal(num1) {
        return (1/num1);
    }


}
}
public static void main(String[]args) {