Table of contents
1. Use placeholders for basic string formatting:
2. Control the precision and decimal places of floating-point numbers:
5. Format numbers with thousands separators:
9. Control the precision and decimal places of floating-point numbers:
11. Use placeholders to fill strings:
14. Format floating point numbers:
15. Use commas to separate numbers:
21. Custom formatting options:
23. Format the date to the specified format:
25. Add signs to positive and negative numbers:
26. Format scientific notation:
27. Format hexadecimal numbers:
32. Format numbers according to different locales:
33. Format the date as a custom format:
34. Format the time as a custom format:
35. Format scientific notation:
36. Time zone for formatting dates and times:
37. Format numbers into different bases:
1. Use placeholders for basic string formatting:
String name = "Alice";
int age = 25;
String message = String.format("My name is %s and I am %d years old.", name, age);
Note: Use %s to represent a string and %d to represent an integer, and you can insert the value of the variable into the string.
2. Control the precision and decimal places of floating-point numbers:
double num = 3.141592653589793;
String message = String.format("The value of pi is approximately %.2f.", num);
Note: Use %.2f to format floating point numbers to two decimal places.
3. Format date and time:
import java.time.LocalDateTime;
String date = LocalDateTime.now().toString();
String message = String.format("Today's date and time is %s.", date);
Notes: Use the LocalDateTime class to get the current date and time and use %s to format it as a string.
4. Align text:
String name = "Alice";
int age = 25;
String message = String.format("Name: %-10s, Age: %d", name, age);
Note: Use %-10s to left-justify strings, and use %d to format integers.
5. Format numbers with thousands separators:
int num = 1000000;
String message = String.format("The population is %,d.", num);
Note: Use %,d to format numbers with thousands separators.
6. Format currency:
import java.util.Currency;
import java.util.Locale;
double amount = 1000.50;
Currency currency = Currency.getInstance(Locale.US);
String message = String.format("The price is %s%.2f.", currency.getSymbol(), amount);
Note: Use the Currency class to get the currency symbol and format the floating point number as currency.
7. Format percentage:
double percentage = 0.75;
String message = String.format("The discount is %.2f%%.", percentage * 100);
Note: Use %.2f%% to format floating point numbers as percentages.
8. Basic string formatting:
String name = "Alice";
int age = 25;
String message = String.format("My name is %s and I am %d years old.", name, age);
System.out.println(message);
Note: Use %s to represent a string and %d to represent an integer, and insert the value of the variable into the string. operation result:My name is Alice and I am 25 years old.
9. Control the precision and decimal places of floating-point numbers:
double num = 3.141592653589793;
String message = String.format("The value of pi is approximately %.2f.", num);
System.out.println(message);
Note: Use %.2f to format floating point numbers to two decimal places. operation result:The value of pi is approximately 3.14.
10. Format date and time:
11. Use placeholders to fill strings:
String name = "Alice";
String message = String.format("Hello, %20s!", name);
System.out.println(message);
Comments: Use %20s to format the string as a field of length 20, right-padded with spaces. operation result:Hello, Alice!
12. Align text:
String name = "Alice";
String message = String.format("|%10s|", name);
System.out.println(message);
Comments: Use %10s to format strings into fields of length 10, padded with spaces on the left. operation result:| Alice|
13. Format integers:
int number = 42;
String message = String.format("The answer to life, the universe, and everything is %d.", number);
System.out.println(message);
Note: Use %d to format integers as strings. operation result:The answer to life, the universe, and everything is 42.
14. Format floating point numbers:
double number = 3.141592653589793;
String message = String.format("The value of pi is approximately %.4f.", number);
System.out.println(message);
Note: Use %.4f to format floating point numbers to four decimal places. operation result:The value of pi is approximately 3.1416.
15. Use commas to separate numbers:
int number = 1000000;
String message = String.format("One million is written as %,d.", number);
System.out.println(message);
Note: Use %,d to format numbers as strings with thousands separators. operation result:One million is written as 1,000,000.
16. Format date and time:
import java.time.LocalDateTime;
String dateTime = LocalDateTime.now().toString();
String message = String.format("Current date and time: %tF %tT", dateTime, dateTime);
System.out.println(message);
Note: Use %tF and %tT to format date and time in ISO 8601 format (eg: 2022-01-01 12:34:56). operation result:Current date and time: 2022-01-01 12:34:56
17. Format percentage:
double percentage = 0.75;
String message = String.format("The discount is %.2f%%.", percentage * 100);
System.out.println(message);
Note: Use %.2f%% to convert decimals to percentages and keep two decimal places. operation result:The discount is 75.00%.
18. Format boolean values:
boolean isTrue = true;
String message = String.format("The value of the boolean is %b.", isTrue);
System.out.println(message);
Note: Use %b to format booleans as strings. operation result:The value of the boolean is true.
19. Nested formatting:
int number = 42;
String message = String.format("The answer to life, the universe, and everything is %d, which is %.2f%% of %s.", number, (double)number / 100, "100");
System.out.println(message);
Note: Multiple placeholders are nested within the format string. operation result:The answer to life, the universe, and everything is 42, which is 0.42% of 100.
20. Format currency amount:
import java.text.NumberFormat;
double amount = 1234.56;
NumberFormat currencyFormatter = NumberFormat.getCurrencyInstance();
String message = String.format("The total amount is %s.", currencyFormatter.format(amount));
System.out.println(message);
Note: Use the NumberFormat class and the getCurrencyInstance() method to format numbers as currency amounts. operation result:The total amount is $1,234.56.
21. Custom formatting options:
String name = "Alice";
int age = 25;
String message = String.format("Hello, %s! You are %02d years old.", name, age);
System.out.println(message);
Note: Use %02d to format integers as two digits with leading zeros. operation result:Hello, Alice! You are 25 years old.
22. Format multiple objects:
int apples = 5;
int oranges = 3;
String message = String.format("I have %d apples and %d oranges.", apples, oranges);
System.out.println(message);
Note: Use multiple placeholders in the format string and provide the corresponding arguments in order. operation result:I have 5 apples and 3 oranges.
23. Format the date to the specified format:
import java.time.LocalDate;
String date = LocalDate.now().toString();
String message = String.format("Today's date is %s.", date);
System.out.println(message);
Note: Use %s to format dates as strings. operation result:Today's date is 2022-01-01.
24. Align text:
String name = "John";
String message = String.format("Hello, %10s!", name);
System.out.println(message);
Note: Use %10s to right-justify the string and pad spaces on the left (if the string is less than 10 characters). operation result:Hello, John!
25. Add signs to positive and negative numbers:
int positiveNumber = 42;
int negativeNumber = -42;
String message = String.format("Positive: %+d, Negative: %+d", positiveNumber, negativeNumber);
System.out.println(message);
Note: Use %+d to display the sign (+/-) for both positive and negative numbers. operation result:Positive: +42, Negative: -42
26. Format scientific notation:
double number = 1.23456789E10;
String message = String.format("Scientific notation: %.2e", number);
System.out.println(message);
Note: Use %.2e to format numbers in scientific notation and specify the number of digits after the decimal point. operation result:Scientific notation: 1.23e+10
27. Format hexadecimal numbers:
int number = 255;
String message = String.format("Hexadecimal: %x", number);
System.out.println(message);
Note: Use %x to format integers as hexadecimal. operation result:Hexadecimal: ff
28. Format percentage:
double percentage = 0.75;
String message = String.format("Percentage: %.2f%%", percentage * 100);
System.out.println(message);
Note: Use %.2f to format decimals as percentages, and multiply by 100 to convert to percentages. operation result:Percentage: 75.00%
29. Format date and time:
import java.time.LocalDateTime;
LocalDateTime dateTime = LocalDateTime.now();
String message = String.format("Current date and time: %tF %tT", dateTime, dateTime);
System.out.println(message);
Note: Use %tF and %tT to format the date and time to the specified format. operation result:Current date and time: 2022-01-01 12:34:56
30. Format left alignment:
String name = "Alice";
String message = String.format("Hello, %-10s!", name);
System.out.println(message);
Note: Use %-10s to left-justify the string and pad spaces on the right if the string is less than 10 characters long. operation result:Hello, Alice !
31. Format currency amount:
import java.text.NumberFormat;
double amount = 12345.67;
String message = String.format("Amount: %s", NumberFormat.getCurrencyInstance().format(amount));
System.out.println(message);
Note: Use the getCurrencyInstance() method of the NumberFormat class to get an instance of the formatted currency and format the amount in currency format. operation result:Amount: $12,345.67
32. Format numbers according to different locales:
import java.text.NumberFormat;
double amount = 12345.67;
NumberFormat numberFormat = NumberFormat.getNumberInstance(Locale.FRENCH);
String message = String.format("Amount: %s", numberFormat.format(amount));
System.out.println(message);
Note: Use the getNumberInstance() method of the NumberFormat class to get an instance of a specific locale and format the number to that locale's format. Running results (in the French environment):Amount: 12 345,67
33. Format the date as a custom format:
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
LocalDate date = LocalDate.now();
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy");
String message = String.format("Custom date format: %s", date.format(formatter));
System.out.println(message);
Note: Use the ofPattern() method of the DateTimeFormatter class to create an instance of a custom date format and format the date to that custom format. operation result:Custom date format: 01/01/2022
34. Format the time as a custom format:
import java.time.LocalTime;
import java.time.format.DateTimeFormatter;
LocalTime time = LocalTime.now();
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("HH:mm:ss");
String message = String.format("Custom time format: %s", time.format(formatter));
System.out.println(message);
Note: Use the ofPattern() method of the DateTimeFormatter class to create an instance of a custom time format and format the time to that custom format. operation result:Custom time format: 12:34:56
35. Format scientific notation:
double number = 12345.6789;
String message = String.format("Scientific notation: %.2e", number);
System.out.println(message);
Note: Use %.2e to format numbers in scientific notation and specify the number of digits after the decimal point. operation result:Scientific notation: 1.23e+04
36. Time zone for formatting dates and times:
import java.time.ZonedDateTime;
ZonedDateTime dateTime = ZonedDateTime.now();
String message = String.format("Date and time with timezone: %tF %tT %tz", dateTime, dateTime, dateTime);
System.out.println(message);
Note: Use %tF, %tT, and %tz to format date, time, and time zone information into the specified format. operation result:Date and time with timezone: 2022-01-01 12:34:56 +0800
37. Format numbers into different bases:
int number = 255;
String message = String.format("Binary: %s, Octal: %s", Integer.toBinaryString(number), Integer.toOctalString(number));
System.out.println(message);
Note: Use the toBinaryString() and toOctalString() methods of the Integer class to format numbers in binary and octal. operation result:Binary: 11111111, Octal: 377