About string format(String format, Object... args)

I recently saw this method in the code of the previous system , I think it's not bad , Make a note of .

This has two main uses ：

1. String.format(String format, Object... args) Returns a format string with the specified format string and parameters .（ Default to local language ）
2. String.format(Locale l, String format, Object... args) Use the specified language environment 、 Format string and parameters return a format string . （ Use Locale You can specify the language .）

From the source code, you can see that this method is from JDK 1.5 Introduced , At the bottom is the call java.util.Formatter Class format Method .

    /**
     * Returns a formatted string using the specified format string and
     * arguments.
     *
     * @return  A formatted string
     *
     * @see  java.util.Formatter
     * @since  1.5
     */
    public static String format(String format, Object... args) {
        return new Formatter().format(format, args).toString();
    }


    public static String format(Locale l, String format, Object... args) {
        return new Formatter(l).format(format, args).toString();
    }

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General types 、 The syntax of the format specifiers for character types and numeric types is as follows ：%[argument_index$][flags][width][.precision]conversion

Optional argument_index It's a decimal integer , Used to indicate the position of the parameter in the parameter list . The first parameter consists of "1$" quote , The second parameter consists of "2$" quote , And so on .

Optional flags Is to modify the character set of the output format . The set of valid flags depends on the conversion type .

Optional width Is a nonnegative decimal integer , Indicates the minimum number of characters to write to the output .

Optional precision Is a nonnegative decimal integer , Usually used to limit the number of characters . The specific behavior depends on the type of transformation .

what is needed conversion Is a character that indicates how the parameter should be formatted . The valid conversion set for a given parameter depends on the data type of the parameter .

• s： character string
• o: Octal numbers
• x： Hexadecimal number
• d： Decimal number

The syntax for the format specifier used to represent date and time types is as follows ：%[argument_index$][flags][width]conversion

Optional argument_index、flags and width As defined above .

The required conversion It's a two character sequence . The first character is 't' or 'T'. The second character indicates the format used . These characters are similar to but not exactly equivalent to those by GNU date and POSIX strftime(3c) Defined characters .

The syntax of a format specifier that does not correspond to a parameter is as follows ：%[flags][width]conversion

Optional flags and width As defined above .

The required conversion Is a character indicating what to insert in the output .

More usage can be found in JDK Document address ：https://tool.oschina.net/apidocs/apidoc?api=jdk-zh Subsequent use will be updated in succession .

Here are some examples to illustrate ：

String.format("My name is %s%s", "li", "xj")    ---> My name is lixj

String.format("%1$s,%2$s", " Workers ", " Working soul "))        -->  Workers , Working soul 
String.format("%2$s,%1$s", " Workers ", " Working soul ")        -->  Working soul , Workers 

String.format("%o", 12))        --> 14  （10 Turn into the system 8 Base number ）

String.format("%x", 12))        --> c  （10 Turn into the system 16 Base number ）

String.format("%1$,d", 5645645)        --> 5,645,645 (flag  Usage of , It's easy to separate here , Translates into 10 Base number .）

String.format("%1$08d", 21729)        --> 00021729

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