JAVA string formatting - the use of String.format()

JAVA string formatting - the use of String.format()

introduction

Methods of the String class format()are used to create formatted strings and concatenate multiple string objects. Familiar with C language should remember sprintf()the method of C language, the two have similarities. format()There are two overloaded forms of the method.

overload

// 使用当前本地区域对象（Locale.getDefault()），制定字符串格式和参数生成格式化的字符串
String String.format(String fmt, Object... args);

// 自定义本地区域对象，制定字符串格式和参数生成格式化的字符串
String String.format(Locale locale, String fmt, Object... args);

Placeholder

The format description can have up to 5 parts (excluding the % symbol). The [] symbols below are all optional items, so only % and type are necessary. The order of the format description is specified and must be Chapter specified in this order.

Example:

When there are more than one parameter, add the new parameter to the back, so there will be 3 parameters to call format()instead of two, and in the first parameter, that is, in the format string, there will be two different formats Optimization setting, that is, a combination of characters beginning with two %, the second one will be applied to the first %, and the third parameter will be used on the second %, that is, the parameters will be applied to the above in order. %"

 int one = 123456789;
 double two = 123456.789;
 String s = String.format("第一个参数：%,d 第二个参数：%,.2f", one, two);
 System.out.println(s);

conversion character

Converter flag

Format the string

Example - will "hello"format as "hello "(left-aligned)

  String raw = "hello word";
  String str = String.format("|%-15s|", raw);
  System.out.println(str);

Format an integer

Example - Display -1000 as (1,000)

int num = -1000;
String str = String.format("%(,d", num);
System.out.println(str);

[

Format floating point numbers

double num = 123.456789;
System.out.print(String.format("浮点类型：%.2f %n", num));
System.out.print(String.format("十六进制浮点类型：%a %n", num));
System.out.print(String.format("通用浮点类型：%g ", num));

Format datetime

• Date Converter

• time converter

example

Date date = new Date();  
System.out.printf("全部日期和时间信息：%tc%n",date);  
System.out.printf("年-月-日格式：%tF%n",date);  
System.out.printf("月/日/年格式：%tD%n",date);  
System.out.printf("HH:MM:SS PM格式（12时制）：%tr%n",date);  
System.out.printf("HH:MM:SS格式（24时制）：%tT%n",date);  
System.out.printf("HH:MM格式（24时制）：%tR",date);