为什么在 for 循环中初始化变量时，我会收到“变量可能没有为变量 a、b 和 n 初始化”？

Question

I tried to take input by stdin and I want "t" times the value of a , b and n . But I am getting compile error the variable might not have been initialized for the variables a , b and n .

I am not able to figure out where I went wrong.

import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*; 

public class Solution {

    public static void main(String[] args) {
        /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
        int num;
        Scanner in = new Scanner(System.in);
        num = in.nextInt();             
        int sol;             
        sol=  takken(num);
        System.out.println(sol);
    }

    public static int takken(int howManyTimes){
        int a, b, n;
        int x;
        int solution = 0;
        Scanner d = new Scanner(System.in);
        int y = 4;
        for(int j = 0; j< y; j++)
        {
            a = d.nextInt();
            b = d.nextInt();
            n = d.nextInt();
        }
        solution = a;
        int temp = 0;

        for ( int i = 0; i < n; i++ ){
            x = (int) Math.pow(2,i);
            temp =  x * b;

            solution = solution + temp;
        }
        return solution;
    }
}

Answer 1

Just change your declaration of a , b and n to:

int a = 0, b = 0, n = 0;

The Java compiler cannot tell that you have initialized these variables in the for-loop because you are going through the for-loop a variable number of times (that number being the variable y ).

Although you declared y to have the value 4 just above the for-loop, and we can see that this means that your variables will always get a value, this is not seen by the Java compiler.

The Java compiler follows a number of strict rules when checking whether something is certain to have been initialized; and if you initialize them in a loop that is iterated over a variable number of times, even if the variable is set before, Java still doesn't see that.