如何解决这些错误

Question

I have a program that adds 2 numbers in Java and outputs the sum. (The numbers are input through keyboard). However, I have an error that I need help resolving. I'll explain the error after the code:

package com.sigma.java7;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Addition {

    public static void main(String[] args) throws IOException {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    do {
        try {
           System.out.println("Enter A :");
           String numA = br.readLine();
           int a = Integer.parseInt(numA);
           break;
        } catch (Exception e) {
           System.out.println("Incorrect input. Please enter an integer.");
        }
    } while (true);
    do {
        try {
           System.out.println("Enter B :");
           String numB = br.readLine();
           int b = Integer.parseInt(numB);
           break;
        } catch (Exception e) {
           System.out.println("Incorrect input. Please enter an integer.");
        }
    } while (true);
    System.out.println("The sum of the numbers is: " +(a+b));
    br.close();
  }
}

In the line

"System.out.println("The sum of the numbers is: " +(a+b));" 

I'm getting the errors: "a cannot be resolved to a variable and b cannot be resolved to a variable." WHY?

Answer 1

You have bad variable scope. When you define local variables it will work only work in a same block. ex.

{
    int i = 2;
    {
       int k = 4;
       // i can be accessed here.
    }
    // i can be accessed here.
    // k can not be accessed here.    
}

Answer 2

That's a compile time error caused by variable scope issues: a is defined inside the first try block, and is thus not visible outside that block.

As this has an assignment smell just a tip: move it to an outer scope and your problem will be solved..

Answer 3

在外部作用域中定义a和b，以便在打印时可以访问它。

Answer 4

Before you first do while loop add:

int a,b;

This will declare the variables to have scope outside of the loops so you can access them anywhere inside the method, instead of just a local loop. If you add this line of code, replace

int a  = Integer.parseInt(numA);

with:

a  = Integer.parseInt(numA);

and the same thing for b