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Format a String (JDK1.5)Tag(s): String/Number


JDK1.5 simplifies the operation of formatting a String based on parameters.

The String class now provides a new method called format(). The parameter substitution mechanism is heavily inspired by C's printf. 

 String s = String.format
   ("Welcome %s at %s", "Real's HowTo", "http://www.rgagnon.com");
 System.out.println(s);
 // output : Welcome Real's HowTo at http://www.rgagnon.com

A printf method has been added to System.out ! 

System.out.printf
  ("Welcome %s at %s", "Real's HowTo", "http://www.rgagnon.com");

As you can see, it is now possible to call a method with a variable number of parameters. But it is also possible to use an array (with the new String.format()). 


String a[] = { "Real's HowTo", "http://www.rgagnon.com" };

String s = String.format("Welcome %s at %s", a);
System.out.println(s);


Object a[] = { "Real's HowTo", "http://www.rgagnon.com" ,
        java.util.Calendar.getInstance()};

String s = String.format("Welcome %1$s at %2$s ( %3$tY %3$tm %3$te )", a);
System.out.println(s);
//  output : Welcome Real's HowTo at http://www.rgagnon.com (2010 06 26)

You can use this new feature to quickly format strings into table : 

public class Divers {
  public static void main(String args[]){
      String format = "|%1$-10s|%2$-10s|%3$-20s|\n";
      System.out.format(format, "FirstName", "Init.", "LastName");
      System.out.format(format, "Real", "", "Gagnon");
      System.out.format(format, "John", "D", "Doe");

      String ex[] = { "John", "F.", "Kennedy" };

      System.out.format(String.format(format, (Object[])ex));
  }
}
Output: 
|FirstName |Init.     |LastName            |
|Real      |          |Gagnon              |
|John      |D         |Doe                 |
|John      |F.        |Kennedy             |
To align numbers : 
  String format = "%10.2f\n"; // width == 10 and 2 digits after the dot
  float [] floats = {123.45f, 99.0f, 23.2f, 45.0f};
  for(int i=0; i<floats.length; i++) {
    float value = floats[i];
    System.out.format(format, value);
  }
Output : 
    123.45
     99.00
     23.20
     45.00