Type conversion problem in Java - how to solve java.lang.NumberFormatException?

In Java development, we often encounter type conversion problems. When we convert a value of one data type to a value of another data type, if the conversion is incorrect, a java.lang.NumberFormatException exception will be thrown. This article will describe the cause of this exception and how to avoid it.

java.lang.NumberFormatException exception reason

java.lang.NumberFormatException exception indicates that an error occurred in converting a string to a number. Normally, we use basic data type parsing methods such as Integer.parseInt(String) or Double.parseDouble(String) to convert strings into numbers. However, if the string contains non-numeric characters or is formatted incorrectly, a Number Format Exception will occur.

For example, the following code:

String str = "abc";
int num = Integer.parseInt(str);

During the running process, a java.lang.NumberFormatException exception will occur. Because the string "abc" cannot be parsed into a number.

Solution to java.lang.NumberFormatException exception

For java.lang.NumberFormatException exception, we can take the following methods to solve it:

1. Use try-catch Block

We can put the string that needs to be converted in the try code block, and then catch the exception in the catch code block. For example, the following code:

String str = "abc";
try {
    int num = Integer.parseInt(str);
} catch (NumberFormatException e) {
    System.out.println("字符串无法转换成数字");
}

By using try-catch blocks, we can catch exceptions and handle them to avoid program crashes.

2. Use regular expressions to filter out invalid characters

In order to avoid invalid characters in the string, we can use regular expressions to filter out these characters. For example, the following code:

String str = "abc123";
str = str.replaceAll("[^\d+]", "");
int num = Integer.parseInt(str);

In this example, we use the replaceAll() method to replace non-numeric characters in the string with an empty string. We can then call the Integer.parseInt() method to convert the converted string into a number.

3. Use the official API

In addition to the parsing methods of basic data types, the Java API also provides some other methods to convert strings into numbers. These methods can handle some formatting issues to avoid the occurrence of java.lang.NumberFormatException. For example, the following code:

String str = "123.45";
double num = Double.parseDouble(str);

In this example, we use the Double.parseDouble() method to convert a string into a floating point number.

Summary

The type conversion problem in Java is a problem we often encounter in development. When we try to convert a value of one data type to a value of another data type, if the conversion is incorrect, a java.lang.NumberFormatException may be thrown. In order to avoid this situation from happening, we can use try-catch blocks or use regular expressions to filter invalid characters to solve this problem. In addition, the Java API also provides some methods to handle type conversion issues, which we can use as needed.

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