Formatting

Introduction

• String formatting can be done using the printf() and the format() methods added in java.io.PrintStream (System.out is a PrintStream)
• Internally they ise the java.util.Formatter class.
• Basic format:

printf("format string", argument(s));

• It can be cleaner to use:

• When we want to use variables and strings in a print, it can get irritating to keep concatenating and keeping the whitespaces and commas in mind:

System.out.println("The sum of " + i + " and " + j + " is " + (i+j));

• A printf, can make things easier:

System.out.printf("The sum of %d and %d is %d", i, j, (i+j));

Format String

• Syntax:

%[arg_index$][flags][width][.precision] conversion_char

• Every argument must have a format string in the above syntax, or it wont be printed!

Arguments within [] are optional. Only the conversion_char is mandatory. The following are the conversion chars:

• b - boolean
• c - char
• d - integer
• f - floating point
• s - string

Optional arguments

• arg_index is the number of the argument followed by a $. The no starts from 1.
• example:

System.out.printf("%2$s , %1$s", "Suhrid", "Karthik");
//Prints : Karthik, Suhrid

• flags
  • "-" : Left justify
  • "+" : Include a sign
  • "0" : Pad with zeroes
  • "," : Use locale specific group separators
  • "(" : Enclose -ve numbers in brackets

• examples:

int i = 11;
int j = -22;
out.printf("%+d , %+d", i, j);
//prints: +11 , -22