Java 中的变量无法识别

Question

我正在创建一个命令行程序来将输入的温度从摄氏度 (C) 更改为华氏度 (F)，反之亦然。该程序运行良好，直到用户输入临时类型 (C/F)，然后它似乎无法识别用户输入。我做错了什么？

public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        System.out.println("Please enter the temperature:"); //Prompts user for temperature
        String temp = input.nextLine(); //Allows user to input temp data
        double tempDouble = Double.parseDouble(temp); //Changes input from string to double

        System.out.println("Is " + temp + " degrees in Celsius or Fahrenheit? (Enter C or F):"); //Prompts user for type of temp
        String type = input.nextLine(); //Allows user to input temp type

        if (type == "C") { //Checks if temp is Celsius
            double tempF = 0;
            tempF = (tempDouble * 1.8) + 32; //Converts temp to Fahrenheit
            System.out.println(tempDouble + "C equals " + tempF + "F."); //Displays conversion of C to F
            //Tf = Tc * 1.8 + 32

        } else if (type == "F") { //Checks if temp is Fahrenheit
            double tempC = 0;
            tempC = (tempDouble - 32) / 1.8; //Converts temp to Celsius
            System.out.println(tempDouble + "F equals " + tempC + "C.");
            //Tc = (Tf - 32) / 1.8
        }
        System.out.println("Incorrect input for Celsius or Fahrenheit"); //Tells user they didn't input C or F correctly
    }

Answer 1

代码中有两个问题

您正在检查对象是否相等，而不是对象的值。用户 String.equals 方法。
if-else 块的构造是错误的，它总是打印“Incorrect input for Celsius or Fahrenheit”。

这是正确的 -

public static void main(String[] args) {
    Scanner input = new Scanner(System.in);

    System.out.println("Please enter the temperature:"); //Prompts user for temperature
    String temp = input.nextLine(); //Allows user to input temp data
    double tempDouble = Double.parseDouble(temp); //Changes input from string to double

    System.out.println("Is " + temp + " degrees in Celsius or Fahrenheit? (Enter C or F):"); //Prompts user for type of temp
    String type = input.nextLine(); //Allows user to input temp type

    if ("C".equals(type)) { //Checks if temp is Celsius
        double tempF = 0;
        tempF = (tempDouble * 1.8) + 32; //Converts temp to Fahrenheit
        System.out.println(tempDouble + "C equals " + tempF + "F."); //Displays conversion of C to F
        //Tf = Tc * 1.8 + 32

    } else if ("F".equals(type)) { //Checks if temp is Fahrenheit
        double tempC = 0;
        tempC = (tempDouble - 32) / 1.8; //Converts temp to Celsius
        System.out.println(tempDouble + "F equals " + tempC + "C.");
        //Tc = (Tf - 32) / 1.8
    }else{
        System.out.println("Incorrect input for Celsius or Fahrenheit"); //Tells user they didn't input C or F correctly 
    }
}

Java 中的变量无法识别

Variable in Java Not Recognized

java

variables

if-statement

user-input

command-line-arguments