在For循环（Java）中初始化变量

Question

I need to create a program that takes in 4 integers from the user and makes sure if the input is between 0 and 255 exclusive. Everything is working except for my final output, the IP address which is pretty much all of the inputs in one string. It keeps printing out 0 because I had to initialize my variables before using them in an array, so I assigned them the value of 0. However, the value was supposed to change in the for loop, but it still prints out the incorrect value. I can only print out the IP address once and it has to be at the end. I know that there is an easier way of doing this, but I still want to know how fix this issue for future reference. The following is my code:

import java.util.Scanner;

class Main {

public static void main(String[] args) {
    Scanner run = new Scanner(System.in);
    String per = ".";
    int firstInput = 0;
    int secondInput = 0;
    int thirdInput = 0;
    int fourthInput = 0;
    boolean firstMeetsParameters = true;
    boolean secondMeetsParameters = true;
    boolean thirdMeetsParameters = true;
    boolean fourthMeetsParameters = true;
    int[] inputs = new int[] {firstInput,secondInput,thirdInput,fourthInput};
    boolean[] condition = new boolean[] {firstMeetsParameters,secondMeetsParameters,thirdMeetsParameters,fourthMeetsParameters};
    String[] num = new String[] {"first", "second", "third", "fourth"};
    for(int x = 0; x < inputs.length; x++) {
        System.out.println("Please enter the " + num[x] + " octet:");
        inputs[x] = run.nextInt();
        if(inputs[x] < 0 || inputs[x] > 255) {
            condition[x] = false;
        }
    }
    for(int i = 0; i < inputs.length; i++){
        if(condition[i] == false) {
            System.out.println("Octet " + (i+1) + " is incorrect.");
        }        
    }
    System.out.println("IP Address: " + firstInput + per + secondInput + per + thirdInput + per + fourthInput);    
}

}

Answer 1

run this code and be enlightened:

int x = 0;
int[] a = new int[] {x};
x = 1;
System.out.println(a[0]); // What do you think.. does this print 0 or 1?
a[0] = 2;
System.out.println(x); // What do you think.. does this print 1 or 2?

Once you understand that new int[] {x}; does not 'link' x and the first slot of array a together, and that new int[] {x}; in the above is no different than new int[] {0}, you should be able to figure out why it's not working: You're assigning the user inputs into the 4 slots of the inputs[] array, and you never touch the firstInput variable at all, until you print it, at which point it is obviously still what it was when you created it: 0.

Answer 2

You never set the values of firstInput, secondInput etc.

If you change your output statement to the following it works.

System.out.println("IP Address: " + inputs[0] + per + inputs[1] + per + inputs[2] + per + inputs[3]);

Answer 3

The problem is on variable reference. You are setting the values at the inputs array, but print variables firstInput, secondInput... As they are native types there's no reference between them. You should print using the inputs array like this:

System.out.println("IP Address: " + inputs[0] + per + inputs[1] + per + inputs[2] + per + inputs[3]);

The value set on inputs[0] does not change the value on firstInput variable.