MessageFormat format() method in Java with Example : Set – 1

The format() method of java.text.MessageFormat class is used to get the formatted array of object appended into the string buffer object. formatted array will contain all forms of element lies in the pattern of MessageFormat object.
Syntax:

public final StringBuffer format(Object[] arguments,
                                 StringBuffer result,
                                 FieldPosition pos)

Parameter:  

• argument :– This method takes array object as a parameter for which formatting is going to take place.
• result :- string buffer will be use for appending the formatted array.
• pos :- field position will be going to use for alignment purpose.

Return Value: This method returns string buffer which will have the appended result of formatted array.
Exception: This method throws NullPointerException if the result is null.
Below are the examples to illustrate the format() method:
Example 1:

Java

// Java program to demonstrate
// format() method

import java.text.*;
import java.util.*;
import java.io.*;

public class GFG {
    public static void main(String[] argv)
    {
        try {
            // creating and initializing new MessageFormat Object
            MessageFormat mf
                = new MessageFormat("{0, number, #}, {0, number, #.##}, {0, number}");

            // Creating and initializing new FieldPosition Object
            FieldPosition fp
                = new FieldPosition(MessageFormat.Field.ARGUMENT);

            // Creating and initializing an array of type Double
            // to be formatted
            Object[] objs = { new Double(9.5678) };

            // Creating and initializing StringBuffer for
            // appending the result
            StringBuffer stb = new StringBuffer(10);

            // Formatting an array of object
            // using format() method
            stb = mf.format(objs, stb, fp);

            // display the result
            System.out.println("formatted array : "
                               + stb.toString());
        }
        catch (NullPointerException e) {

            System.out.println("Exception thrown : " + e);
        }
    }
}

Example 2:

Java

// Java program to demonstrate
// format() method

import java.text.*;
import java.util.*;
import java.io.*;

public class GFG {
    public static void main(String[] argv)
    {
        try {
            // creating and initializing new MessageFormat Object
            MessageFormat mf
                = new MessageFormat("{0, number, #}, {0, number, #.##}, {0, number}");

            // Creating and initializing new FieldPosition Object
            FieldPosition fp
                = new FieldPosition(MessageFormat.Field.ARGUMENT);

            // Creating and initializing an array of type Double
            // to be formatted
            Object[] objs = { new Double(9.5678) };

            // Creating and initializing StringBuffer for
            // appending the result
            StringBuffer stb = new StringBuffer(10);

            // Formatting an array of object
            // using format() method
            stb = mf.format(objs, null, fp);

            // display the result
            System.out.println("formatted array : "
                               + stb.toString());
        }
        catch (NullPointerException e) {
            System.out.println("StringBuffer is null " + e);
            System.out.println("Exception thrown : " + e);
        }
    }
}

Output:

old pattern : {0, date, #}, {1, date, #}, {0, number}

String is Null
StringBuffer is null java.lang.NullPointerException
Exception thrown : java.lang.NullPointerException

Reference: https://docs.oracle.com/javase/9/docs/api/java/text/MessageFormat.html#format-java.lang.Object:A-java.lang.StringBuffer-java.text.FieldPosition-