Solution to Java formatted output exception (FormattedOutputException)

Solution to Java formatted output exception (FormattedOutputException)

In Java programming, we often need to format the output data so that the output information Easier to read and understand. However, sometimes we may encounter an exception called FormattedOutputException, which indicates that an error occurred during the formatted output process. This article will introduce the cause and solution of this exception, and give corresponding code examples.

1. Analysis of exception causes
FormattedOutputException exception usually occurs when formatting output using the format() method of the String class. When we use the format() method, we usually pass in a format string and corresponding parameters. However, when the placeholder in the format string does not match the actual parameter type, a FormattedOutputException exception occurs.

2. Solution
To solve the FormattedOutputException exception, we need to pay attention to two points: the matching of placeholders in the format string and the actual parameters; the escaping of special characters in the format string .

1. Placeholder and parameter matching
   When we use the placeholder "%s" in the formatted string, it means that it needs to be replaced with a string type parameter. If the actual parameter we pass in is not of string type, a FormattedOutputException will occur. To avoid this problem, we need to choose appropriate placeholders based on the type of the parameter. For example, if the parameter is of integer type, we should use "%d" as the placeholder; if the parameter is of floating point type, we should use "%f" as the placeholder. The following is a sample code:

public class FormattedOutputExample {
    public static void main(String[] args) {
        String name = "Tom";
        int age = 20;
        double height = 1.80;

        // 错误示例，会导致FormattedOutputException异常
        System.out.format("My name is %s, age is %d, height is %f", name, age, height);

        // 正确示例
        System.out.format("My name is %s, age is %d, height is %.2f", name, age, height);
    }
}

In the above sample code, we use three placeholders in the format string: %s, %d, %f. Since the parameter name is a string type, we use "%s" as the placeholder; similarly, the parameter age is an integer type, so we use "%d" as the placeholder; the parameter height is a floating point type. , so we used "%f" as a placeholder and passed ".2" to indicate that only two decimal places are retained.

2. Escape of special characters
   In the formatted string, some special characters need to be escaped, otherwise FormattedOutputException will occur. For example, if we want to output a percent sign "%" in the format string, we need to use "%%" to escape it. The following is a sample code:

public class FormattedOutputExample {
    public static void main(String[] args) {
        double percentage = 0.8;

        // 错误示例，会导致FormattedOutputException异常
        System.out.format("The percentage is %d%", percentage * 100);

        // 正确示例
        System.out.format("The percentage is %d%%", (int)(percentage * 100));
    }
}

In the above sample code, we avoid the occurrence of FormattedOutputException by using "%%" to escape the percent sign %.

3. Summary
When performing Java formatted output, we need to pay attention to the matching of placeholders in the format string and the actual parameters, as well as the escaping of special characters. Only when the placeholder and parameter types match, and special characters are escaped correctly, can FormattedOutputException exceptions be avoided. By rationally using placeholders and escape characters, we can achieve more accurate and readable formatted output in Java programming.

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