Java 为什么这个try语句使用catch语句？_Java_Try Catch_Java.util.scanner_Inputmismatchexception

Java 为什么这个try语句使用catch语句？

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Java 为什么这个try语句使用catch语句？,java,try-catch,java.util.scanner,inputmismatchexception,Java,Try Catch,Java.util.scanner,Inputmismatchexception,我添加了一个try语句，在if的第一部分，我告诉它打印subtract，但它调用catch语句。有人能帮忙吗？请记住，我是一名编码初学者。这是一个完整的结构 import java.util.Scanner; import java.util.InputMismatchException; public class bank { public static void login() { double balance; try {

我添加了一个try语句，在if的第一部分，我告诉它打印subtract，但它调用catch语句。有人能帮忙吗？

请记住，我是一名编码初学者。

这是一个完整的结构

import java.util.Scanner;
import java.util.InputMismatchException;
public class bank {
    public static void login() {
        double balance;
        try {
            boolean subtract;
            boolean amounttaken;
            // This is to see if you want to withdraw money
            System.out.println("Do you want to withdraw money?");
            Scanner SCaddOrWithdraw = new Scanner(System.in);
            subtract = SCaddOrWithdraw.nextBoolean();
            if (subtract) {
                System.out.println("How much would you like to withdraw?");
                Scanner SCamounttaken = new Scanner(System.in);
                amounttaken = SCamounttaken.nextBoolean();
                System.out.println("Subtract");
            } else if (!subtract) {
                System.out.print("Ask for bal");
            }
        } catch (InputMismatchException e) {
            System.out.println("Invalid Input");
        }
    }
}

如果try块中的代码可能引发异常，则可以进行替代。就像在上面的代码中一样，如果有人输入字符串而不是布尔值，它将抛出InputMismatchException，该异常将被捕获到catch块中，您可以将错误消息打印给用户，并整洁地显示出来。：）

这是一个完整的结构

import java.util.Scanner;
import java.util.InputMismatchException;
public class bank {
    public static void login() {
        double balance;
        try {
            boolean subtract;
            boolean amounttaken;
            // This is to see if you want to withdraw money
            System.out.println("Do you want to withdraw money?");
            Scanner SCaddOrWithdraw = new Scanner(System.in);
            subtract = SCaddOrWithdraw.nextBoolean();
            if (subtract) {
                System.out.println("How much would you like to withdraw?");
                Scanner SCamounttaken = new Scanner(System.in);
                amounttaken = SCamounttaken.nextBoolean();
                System.out.println("Subtract");
            } else if (!subtract) {
                System.out.print("Ask for bal");
            }
        } catch (InputMismatchException e) {
            System.out.println("Invalid Input");
        }
    }
}

您已将

subtract

和

amounttake

声明为

boolean

变量，因此它们只能将

true

或

false

作为值，例如，下面给出的是一个示例运行：

try {
    // Statement Which May Throw Exceptions
} catch(Exception e) {
    // If any statement throws the exception
    // Do alternative flow here
}

如果您试图输入一个与

true

或

false

不同的值，您将得到

inputmaschException

我想您需要为变量输入一些十进制数（amount），

amounttake

。如果是，则将其声明为

double

或

float

而不是

boolean

，例如

Do you want to withdraw money?
true
How much would you like to withdraw?
true
Subtract

运行示例：

import java.util.InputMismatchException;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        login();
    }

    public static void login() {
        double balance;
        try {
            boolean subtract;
            double amounttaken;// Changed to double
            // This is to see if you want to withdraw money
            System.out.println("Do you want to withdraw money?");
            Scanner SCaddOrWithdraw = new Scanner(System.in);
            subtract = SCaddOrWithdraw.nextBoolean();
            if (subtract) {
                System.out.println("How much would you like to withdraw?");
                Scanner SCamounttaken = new Scanner(System.in);
                amounttaken = SCamounttaken.nextDouble();// Changed for double
                System.out.println("Subtract");
            } else if (!subtract) {
                System.out.print("Ask for bal");
            }
        } catch (InputMismatchException e) {
            System.out.println("Invalid Input");
        }
    }
}

您已将

subtract

和

amounttake

声明为

boolean

变量，因此它们只能采用

true

或

false