Methods to solve Java string to number exception (NumberFormatException)

In Java programming, we often encounter situations where we need to convert a string to a number. However, when the string cannot be converted to a number correctly, a NumberFormatException is thrown. This exception usually occurs when using parseInt(), parseLong() and other methods, causing the program to fail to run normally. In order to avoid this exception and convert string to number correctly, we can handle it in the following way.

1. Use the try-catch statement to catch exceptions

The try-catch statement is one of the most commonly used ways to handle exceptions. By using a try block to perform the string conversion operation and catching the NumberFormatException exception in the catch block, we can avoid program crashes and perform error handling.

The sample code is as follows:

String strNumber = "123abc";
int number;

try {
    number = Integer.parseInt(strNumber);
    System.out.println("轉(zhuǎn)換后的數(shù)字為: " + number);
} catch (NumberFormatException e) {
    System.out.println("字符串無(wú)法轉(zhuǎn)換為數(shù)字");
    e.printStackTrace();
}

In the above example, we try to convert a string "123abc" that cannot be converted to an integer into a number. When it cannot be converted, the program will throw a NumberFormatException exception, execute the code in the catch, output the error message "String cannot be converted to a number", and print the stack trace of the exception.

2. Use regular expressions for pre-judgment

In practical applications, we can use regular expressions to determine whether a string conforms to the format of a number. If the string does not meet the requirements, the conversion operation will not be performed to avoid throwing a NumberFormatException exception. The following is an example of a regular expression that can match integers and floating point numbers:

public static boolean isNumeric(String str) {
    return str.matches("-?\d+(\.\d+)?");
}

By calling the isNumeric() method to pre-determine whether the string is a number, you can avoid throwing a NumberFormatException exception.

The sample code is as follows:

String strNumber = "123abc";
int number;

if (isNumeric(strNumber)) {
    number = Integer.parseInt(strNumber);
    System.out.println("轉(zhuǎn)換后的數(shù)字為: " + number);
} else {
    System.out.println("字符串無(wú)法轉(zhuǎn)換為數(shù)字");
}

The above code will first call the isNumeric() method for judgment. If the string conforms to the numeric format, it will be converted and the result will be output; otherwise, an error message will be output.

3. Use regular expressions or tool classes for conversion

If the pre-judgment process is cumbersome or cannot meet the requirements, we can use regular expressions or tool classes for conversion operations. For example, use the find() method of the Pattern and Matcher classes, or use the methods of the NumberUtils utility class in the Apache Commons package for conversion.

The sample code is as follows:

import java.util.regex.Pattern;
import java.util.regex.Matcher;
import org.apache.commons.lang3.math.NumberUtils;

String strNumber = "123abc";
int number;

Pattern pattern = Pattern.compile("-?\d+");
Matcher matcher = pattern.matcher(strNumber);

if (matcher.find()) {
    number = Integer.parseInt(matcher.group());
    System.out.println("轉(zhuǎn)換后的數(shù)字為: " + number);
} else {
    System.out.println("字符串無(wú)法轉(zhuǎn)換為數(shù)字");
}

// 或者使用NumberUtils工具類(lèi)
if (NumberUtils.isParsable(strNumber)) {
    number = Integer.parseInt(strNumber);
    System.out.println("轉(zhuǎn)換后的數(shù)字為: " + number);
} else {
    System.out.println("字符串無(wú)法轉(zhuǎn)換為數(shù)字");
}

In the above code, we use regular expressions and the find() method of the Matcher class, or use the method of the NumberUtils tool class in the Apache Commons package for conversion operate. Both ways avoid NumberFormatException exceptions and convert strings to numbers correctly.

To sum up, we can solve the Java string to number exception (NumberFormatException) by using try-catch statements to catch exceptions, using regular expressions for pre-judgment, or using regular expressions or tool classes for conversion. )The problem. Choosing the appropriate solution based on actual needs can ensure the stability and reliability of the program.

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