如果指定了总和，如何使Java忽略先前的指令？

Question

Literally started with Java today, and my professor has given my class the task of modifying some very basic code.

I want to modify the code to make it print a message if the sum of n1 and n2 is 666, but I don't want it to print the actual sum or the message that would normally go attached to it. I saw somewhere around here that a similar question was asked, but the solution doesn't seem to work for me. I have no idea why. Please help.

import java.io.Console;
import java.util.Scanner;


public class FirstProgram{

Console t = new Console();

    public static void main(String[] args)
    {

        System.out.println("Hello out there.");
        System.out.println("I will add two numbers for you.");
        System.out.println("Enter two whole numbers on a line:");

        int n1, n2;

        Scanner keyboard = new Scanner(System.in);
        n1 = keyboard.nextInt( );
        n2 = keyboard.nextInt( );

        //This should print normally when the sum is anything BUT 666

        System.out.println("The sum of those two numbers is");
        System.out.println(n1 + n2);

        //If the sum IS 666, I don't want it to print the above lines, just the one below.

        if (n1 + n2 == 666);

        t.println("Nice try, Satan");
    }
}

It gives two major errors: the constructor Console() is not visible, and that I cannot make a static reference to a non-static field t. I have no idea what any of that means or how to fix it.

Answer 1

You should learn how to make conditional statements. Java will not "ignore" and pass to another thing if you don't tell it how to do that. Remeber: computer can't do anything if one do not tell it to do and how to do that.

You are not initializing n1 and n2, they should be initialized after getting the value from the input.

And as said in the comments, always wrap loops, conditional statements within curly braces{} to make sure the code that will be executed be the one inside braces.

import java.util.Scanner;

    public class FirstProgramm{

                public static void main(String[] args){

                System.out.println("Hello out there.");
                System.out.println("I will add two numbers for you.");
                System.out.println("Enter two whole numbers on a line:");



               Scanner keyboard = new Scanner(System.in);
               int n1 = keyboard.nextInt( );
               int n2 = keyboard.nextInt( );

               //See? the result is stored inside this variable
               int sum = n1 + n2;


                //If the sum is equal 666 then print the message
                if(sum == 666) {
                    System.out.println("Nice try, Satan");
                }else {
                  //Else if the sum is something else, print it
                System.out.println("The sum of those two numbers is");
                System.out.println(sum);
                }


        }

}

You can even play with the operator that the if uses to evaluates the condition:

        if(sum != 666) { //If sum is `not equal to` 666... if the sum is anything else than 666, print it
                System.out.println("The sum of those two numbers is");
                System.out.println(sum);

            }else {// But if it is 666, print what is inside the parentheses

                System.out.println("Nice try, Satan");
            }

Answer 2

I will try to help you out here.

Firstly: the constructor Console() is not visible

I think this is in reference to the fact that Console was not really meant to be accessed like that. The constructor of Console is private , meaning that outside classes cannot access it. To remedy this issue, when you want to print to the console, use System.console .

Secondly: I cannot make a static reference to a non-static field t

This one is a bit difficult to explain to someone new. Your main function is static , which means it can be accessed without having to instantiate the class that contains it. Your variable t is a instance variable, meaning that it can be accessed by every function in the class when the class has be initialized. However, because the main function is static , you cannot access a non-static variable, because it may not be initialized yet. If you want to access a instance variable in a static function, you need to make that variable static as well, making it a class variable, which will always be accessible.

Lastly

To getting your code working, you need to read up on if statements. This is a conditional statement that is basically asking if this statement is true, do this . There is an else if and else statements as well that say else if this statement is true, do this and else do this .

Example of proper if / else if / else statement:

if(iAmTrue == true)
{
    //do this
}
else if(theOtherIAmTrue == true)
{
    //do this
}
else
{
    //do this because everything else was not true
}

So to fix your code, you would need to do this:

if(n1 + n2 == 666)
{
    System.out.println("Nice try, Satan");
}
else
{
    //Put your other print message(s) here.
}

Answer 3

I have rewritten the code for you with a few recommendations to achieve what you need.

import java.util.Scanner;

public class FirstProgram {
  // I have removed the Console variable, you don't need that.
  // System.out.println prints to the console.

  // Use constants for any number or string used to give them meaning
  private static final int DEVILS_NUMBER = 666;

  public static void main(String[] args) {
    System.out.println("Hello out there.");
    System.out.println("I will add two numbers for you.");
    System.out.println("Enter two whole numbers on a line:");

    Scanner keyboard = new Scanner(System.in);
    // declare variables next to where they are used.
    // additionally, never declare more than one variable per line.
    // never do this: int n1, n2;
    int n1 = keyboard.nextInt();
    int n2 = keyboard.nextInt();
    // store the sum in a variable so you can refer to it without doing the sum many times
    int sum = n1 + n2;

    //If the sum IS DEVILS_NUMBER, I don't want it to print the above lines, just the one below.
    // always test the positive possibility first, never the negation
    if (DEVILS_NUMBER == sum) {
      System.out.println("Nice try, Satan");
    } else {
      //This should print normally when the sum is anything BUT DEVILS_NUMBER
      System.out.println("The sum of those two numbers is");
      System.out.println(n1 + n2);
    }
}

Last but not least, have a look at Java Google Style for tips on how to properly format your code. If you are using an IDE like Eclipse, Intellij or NetBeans it can automatically format the code for you.