Java程序: Variable sum may not have been initialized

Question

创建了一个简单的 Java 程序来添加 2 个整数(尚未完成)。我需要专门针对我的变量“sum”的帮助。命令提示符指示它可能尚未初始化，

我在“if 语句”中定义了总和。我还应该如何定义或者我在这里做错了什么？非常感谢任何帮助!

import java.util.Scanner;

public class Calculator {
    public static void main(String[] args){
        //Objective: Calculate whole numbers to add, subtract, divide and multiply
        Scanner kbd1 = new Scanner(System.in);
        Scanner kbd2 = new Scanner(System.in);

        int num1, num2, sum;

        System.out.println("Enter two whole numbers: ");
        num1 = kbd1.nextInt();
        num2 = kbd2.nextInt();

        System.out.println("Now what would you like to do with these numbers? (Please input add, subtract, multiply, or divide)");
        Scanner oper = new Scanner(System.in);
        String operation;
        operation = oper.nextLine();

        if (operation == "add" || operation == "Add")
        {
            sum = num1 + num2;
        }
else
        if (operation == "subtract" || operation == "Subtract")
        {
            if (num1 > num2) {
                sum = num1 - num2;
            } else {
                sum = num2 - num1;
            }
        }
else
        if (operation == "multiply" || operation == "Multiply")
        {
            sum = num1 * num2;
        }
else
        if (operation == "divide" || operation == "Divide")
        {
            sum = num1 / num2;
        }

        System.out.println("The answer is: " + "/n" + sum);
    }
}

更新:

基于 Sotirios Delimanolis、getlost 和其他答案:

import java.util.Scanner;

public class Calculator {
    public static void main(String[] args){
        //Objective: Calculate whole numbers to add, subtract, divide and multiply
        Scanner kbd1 = new Scanner(System.in);
        Scanner kbd2 = new Scanner(System.in);

        int num1, num2, sum;


        System.out.println("Enter two whole numbers: ");
        num1 = kbd1.nextInt();
        num2 = kbd2.nextInt();

        System.out.println("Now what would you like to do with these numbers? (Please input add, subtract, multiply, or divide)");
        Scanner oper = new Scanner(System.in);
        String operation;
        operation = oper.nextLine();

        if (operation.equals("add"))
        {
            sum = num1 + num2;
        }
else
        if (operation.equals("subtract"))
        {
            if (num1 > num2) {
                sum = num1 - num2;
            } else {
                sum = num2 - num1;
            }
        }
else
        if (operation.equals("multiply"))
        {
            sum = num1 * num2;
        }
else
        if (operation.equals("divide"))
        {
            sum = num1 / num2;
        }
else
        {sum = 0;}


        System.out.println("The answer is: " + "/n" + sum);
    }
}

现在这似乎可以工作了，我必须比较字符串而不是从用户输入中获取明确的绝对值。谢谢大家!

Answer 1

System.out.println("The answer is: " + "/n" + sum);

因为你还没有初始化int sum；您不能授予 sum 以初始化内部条件

例子

int y;
if(condition not true){
   y=10;
}
System.out.println(y);

您的代码也是如此。如果 y 未初始化会怎样？

你可以通过初始化sum来修复

int sum=0;

还有一件事不要使用

operation == "add"

用于比较字符串你应该使用

operation.equals("add")