Java Equivalent to .NET's String.Format

Is there an equivalent to .NET's String.Format in Java?

Answers


Have a look at the String.format and PrintStream.format methods.

Both are based on the java.util.Formatter class.

String.format example:

Calendar c = new GregorianCalendar(1995, MAY, 23);
String s = String.format("Duke's Birthday: %1$tm %1$te,%1$tY", c);
// -> s == "Duke's Birthday: May 23, 1995"

System.out.format example:

// Writes a formatted string to System.out.
System.out.format("Local time: %tT", Calendar.getInstance());
// -> "Local time: 13:34:18"

The 10 cent answer to this is:

C#'s

String.Format("{0} -- {1} -- {2}", ob1, ob2, ob3)

is equivalent to Java's

String.format("%1$s -- %2$s -- %3$s", ob1, ob2, ob3)

Note the 1-based index, and the "s" means to convert to string using .toString(). There are many other conversions available and formatting options:

http://download.oracle.com/javase/1.5.0/docs/api/java/util/Formatter.html#syntax


There is MessageFormat.format() which uses the .net notation.


You can also simply use %s for string since the index is an optionnal argument.

String name = "Jon";
int age = 26;
String.format("%s is %s years old.", name, age);

It's less noisy.

Note about %s from the java documentation:

If the argument arg is null, then the result is "null". If arg implements Formattable, then arg.formatTo is invoked. Otherwise, the result is obtained by invoking arg.toString().


There is a String.format in Java, although the syntax is a little different from in .NET.


This isn't really an answer to the OP's question, but may be helpful to others who are looking for a simple way of performing substitution of strings into a string containing C#-style "format items".

   /**
    * Method to "format" an array of objects as a single string, performing two possible kinds of
    * formatting:
    *
    * 1. If the first object in the array is a String, and depending on the number of objects in the
    *    array, then a very simplified and simple-minded C#-style formatting is done. Format items
    *    "{0}", "{1}", etc., are replaced by the corresponding following object, converted to string
    *    (of course). These format items must be as shown, with no fancy formatting tags, and only
    *    simple string substitution is done.
    *
    * 2. For the objects in the array that do not get processed by point 1 (perhaps all of them,
    *    perhaps none) they are converted to String and concatenated together with " - " in between.
    *
    * @param objectsToFormat  Number of objects in the array to process/format.
    * @param arrayOfObjects  Objects to be formatted, or at least the first objectsToFormat of them.
    * @return  Formatted string, as described above.
    */
   public static String formatArrayOfObjects(int objectsToFormat, Object... arrayOfObjects) {

      // Make a preliminary pass to avoid problems with nulls
      for (int i = 0; i < objectsToFormat; i++) {
         if (arrayOfObjects[i] == null) {
            arrayOfObjects[i] = "null";
         }
      }

      // If only one object, just return it as a string
      if (objectsToFormat == 1) {
         return arrayOfObjects[0].toString();
      }

      int nextObject = 0;
      StringBuilder stringBuilder = new StringBuilder();

      // If first object is a string it is necessary to (maybe) perform C#-style formatting
      if (arrayOfObjects[0] instanceof String) {
         String s = (String) arrayOfObjects[0];

         while (nextObject < objectsToFormat) {

            String formatItem = "{" + nextObject + "}";
            nextObject++;
            if (!s.contains(formatItem)) {
               break;
            }

            s = s.replace(formatItem, arrayOfObjects[nextObject].toString());
         }

         stringBuilder.append(s);
      }

      // Remaining objects (maybe all of them, maybe none) are concatenated together with " - "
      for (; nextObject < objectsToFormat; nextObject++) {
         if (nextObject > 0) {
            stringBuilder.append(" - ");
         }
         stringBuilder.append(arrayOfObjects[nextObject].toString());
      }

      return stringBuilder.toString();
   }

(And in case you're curious, I'm using this code as part of a simple wrapper for the Android Log methods, to make it easier to log multiple things in a single log message.)


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