Question

我有以下代码，它适用于整数，但在输入字符串时抛出以下异常：

Exception in thread "main" java.lang.NumberFormatException: For input string: "henry"
   at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
   at java.lang.Integer.parseInt(Integer.java:449)
   at java.lang.Integer.parseInt(Integer.java:499)
   at shipCost.java.shipCost.main(shipCost.java:13)

只允许整数的最佳方法是什么？

package shipCost.java;
import java.io.*;

public class shipCost {

    public static void main(String[] args) {

      String s1 = getInput("enter the item price");
      double input = Integer.parseInt(s1);
   try{ 
        if(input < 100){ 
           double total = input += input * .02;
           System.out.println(total);
      }else{
          double total = input;
          System.out.println(total);
      } 
   }catch(NumberFormatException e){
       System.out.print("You must enter a number");
   }

   }

   private static String getInput(String prompt)
        {
        BufferedReader stdin = new BufferedReader(
                new InputStreamReader(System.in));
        System.out.print(prompt);
        System.out.flush();
        try{
            return stdin.readLine();
        } catch (Exception e){
            return "Error: " + e.getMessage();
        }
    }


}

Answer 1

我建议在try-catch周围设置一个Integer.parseInt()块。这样你知道错误是否为java.lang.NumberFormatException类型，并且可以处理这种情况，而不会限制程序暂停执行和退出其他输入错误的能力。

只需专门为catch设置java.lang.NumberFormatException块，以便不会忽略其他错误：

catch(NumberFormatException e){/*print an error message to user etc.*/}

Answer 2

在解析之前，检查字符串变量s1是否包含数字在Apache常见的NumberUtils中，有一种检查方法。

NumberUtil.isNumber（String str）

https://commons.apache.org/proper/commons-lang/javadocs/api-3.1/org/apache/commons/lang3/math/NumberUtils.html

Answer 3

你可以看到整数的JAVA api。它表明方法parseInt（String s）的参数s应该是Number.Just见下文：

  public static int parseInt(String s) throws NumberFormatException {
        return parseInt(s,10);
  }


  public static int parseInt(String s, int radix)
            throws NumberFormatException {
    /*
     * WARNING: This method may be invoked early during VM initialization
     * before IntegerCache is initialized. Care must be taken to not use
     * the valueOf method.
     */

    if (s == null) {
        throw new NumberFormatException("null");
    }

    if (radix < Character.MIN_RADIX) {
        throw new NumberFormatException("radix " + radix +
                                        " less than Character.MIN_RADIX");
    }

    if (radix > Character.MAX_RADIX) {
        throw new NumberFormatException("radix " + radix +
                                        " greater than Character.MAX_RADIX");
    }

    int result = 0;
    boolean negative = false;
    int i = 0, len = s.length();
    int limit = -Integer.MAX_VALUE;
    int multmin;
    int digit;

    if (len > 0) {
        char firstChar = s.charAt(0);
        if (firstChar < '0') { // Possible leading "+" or "-"
            if (firstChar == '-') {
                negative = true;
                limit = Integer.MIN_VALUE;
            } else if (firstChar != '+')
                throw NumberFormatException.forInputString(s);

            if (len == 1) // Cannot have lone "+" or "-"
                throw NumberFormatException.forInputString(s);
            i++;
        }
        multmin = limit / radix;
        while (i < len) {
            // Accumulating negatively avoids surprises near MAX_VALUE
            digit = Character.digit(s.charAt(i++),radix);
            if (digit < 0) {
                throw NumberFormatException.forInputString(s);
            }
            if (result < multmin) {
                throw NumberFormatException.forInputString(s);
            }
            result *= radix;
            if (result < limit + digit) {
                throw NumberFormatException.forInputString(s);
            }
            result -= digit;
        }
    } else {
        throw NumberFormatException.forInputString(s);
    }
    return negative ? result : -result;
}

Answer 4

试试这个：

package shipcost;

import java.io.*;

//Your class should be ShipCost (All words starting with uppercase)
public class ShipCost {

    public static void main(String[] args) {

    //Declare and initialize your variables first (with invalid values for your program)
    double input = -1;
    double total = 0;
    String s1 = null;

    //This will loop to prompt the user until the input is correct
    while (true) {

        try {

            //try to execute the folowing lines
            s1 = getInput("enter the item price");
            input = Integer.parseInt(s1);

            //If everything went fine, break the loop and move on.
            break;

        } catch (NumberFormatException e) {

            //If the method Integer.parseInt throws the exception, cathc and print the message.
            System.out.println("Not a valid input, please try again.");
        }
    }


    if (input < 100) {

        //What is this line exactly doing?
        //double total = input += input * .02;

        //This is better. If input less than 100, charge 2% over the price.
        total = input * 1.02;

        System.out.println(total);

        //How can you return something from a void method (in this case main).
        //The statement below will not compile
        //return stdin.readLine();

    } else {

        //If greater than or equal to 100, do not charge shiping.
        total = input;
        System.out.println(total);

    }

}

    private static String getInput(String prompt) {

        //Comment your code for your own good, it makes more readable and helps you in future ref.
        BufferedReader stdin = new BufferedReader(
                new InputStreamReader(System.in));

        //Separate your line in chunks for commenting.
        System.out.print(prompt);
        System.out.flush();

        try {
            return stdin.readLine();
        } catch (Exception e) {
            return "Error: " + e.getMessage();
        }
    }

}

仅允许Java中的整数输入

4 个答案: