java - 计算器程序不断得出答案 "0"？

Question

这个问题已经有答案了:

How do I compare strings in Java? (23 个回答)

已关闭 8 年前。

好的，我已经编写了这段代码并检查了很多次，看看是否能找到我的错误。不幸的是，我找不到它，并对自己感到沮丧。我决定将我的代码发布到网上。这是带有方法的实际 Calculator 类。输入类(不在本文中)获取用户输入并将其作为字符串返回。有人可以帮帮我吗？谢谢兄弟。

public class Calculate extends UserInput{

int num1;
int num2;
int returnValue;
String operation;
String userInput1;
String userInput2;

public void calculate() {
    userInput1 = getUserInput("Enter a number: ");
    num1 = Integer.parseInt(userInput1); //Changing userInput to int
    operation = getUserInput("Enter an operation (+,-,*, or /): ");
    userInput2 = getUserInput("Enter a second number: "); //Changing second userInput to int
    num2 = Integer.parseInt(userInput2);

    if(operation == "+") {
        addition(num1, num2);
    } else if (operation == "-") {
        subtraction(num1, num2);
    } else if (operation == "*") {
        multiplication(num1, num2);
    } else if (operation == "/") {
        division(num1, num2);
    }

    System.out.println("Result: " + returnValue);
}

public double addition(int x, int y) {
    returnValue = x + y;
    return returnValue;
}

public double subtraction(int x, int y) {
    returnValue = x - y;
    return returnValue;
}

public double multiplication(int x, int y) {
    returnValue = x * y;
    return returnValue;
}

public double division(int x, int y) {
    returnValue = x / y;
    return returnValue;
}

}

Answer 1

这是我的问题的解决方法!感谢社区!

    if(operation .equals("+")) {
        returnValue = addition(num1, num2);
    } else if (operation .equals("-")) {
        returnValue = subtraction(num1, num2);
    } else if (operation .equals("*")) {
        returnValue = multiplication(num1, num2);
    } else if (operation .equals("/")) {
        returnValue = division(num1, num2);
    }