How does Java use the format() function of the String class to convert data into a string in a specified format?

How does Java use the format() function of the String class to convert data into a string in a specified format?

In Java development, we often encounter situations where we need to convert data into a string in a specified format. Java provides the format() function of the String class, which can convert data into a string according to the specified format. This article will introduce how to use the format() function and demonstrate its usage through code examples.

The format() function of the String class is a static method that can be called directly through the class name. Its syntax is as follows:

public static String format(String format, Object... args)

Among them, the format parameter is a string used to specify the conversion format. The args parameter is a variable parameter used to pass data that needs to be converted.

The format string can contain placeholders, through which data can be inserted into the string according to the specified format. Common placeholders include the following:

• %c: Convert characters to strings.
• %d: Convert integer to string.
• %f: Convert floating point number to string.
• %s: Convert any type of data to a string.

The following is a simple example that demonstrates how to use the format() function to convert data into a string in a specified format:

public class FormatDemo {
    public static void main(String[] args) {
        String name = "Tom";
        int age = 20;
        double score = 95.5;
        
        String result = String.format("姓名：%s，年龄：%d，成绩：%.2f", name, age, score);
        System.out.println(result);
    }
}

In the above code, we define name, age and score three variables, and use the format() function to convert them into strings according to the specified format. The output result is as follows:

姓名：Tom，年龄：20，成绩：95.50

In the format string, %s means inserting the string into this position, %d means inserting the integer into this position, %.2f means insert the floating point number into this position and keep two decimal places.

In addition to basic types of data, we can also use the format() function to convert other types of data. For example, we can convert a date into a string:

import java.util.Date;
import java.text.SimpleDateFormat;

public class FormatDemo {
    public static void main(String[] args) {
        Date now = new Date();
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String result = String.format("当前时间：%s", format.format(now));
        System.out.println(result);
    }
}

In the above code, we use the SimpleDateFormat class to format the current date into a string in a specified format, and use the format() function to insert it into the format character String in. The output result is as follows:

当前时间：2022-01-01 12:34:56

Through the format() function, we can flexibly convert various types of data into strings according to the specified format, and easily output, save or transmit them.

It should be noted that the format() function returns a new string, and the original data will not be affected. In addition, when using placeholders, the number and type of placeholders must correspond one-to-one with the incoming data, otherwise an exception will be thrown.

Summary:
The format() function of the String class in Java can convert data into a string according to the specified format. By using placeholders in the format string, we can flexibly insert various types of data. Using the format() function can conveniently format string output and improve the readability of the code.

I hope this article will help you understand how to use the format() function of the String class to convert data into a string, and I hope you can better apply this function in actual development.

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