Puzzle (No Pain, No Gain)

Consider the following example.

package demo;

import java.util.Random;

public class App {

  public static void main( String[] args ) {
    Random random = new Random();
    StringBuffer word =
      switch ( random.nextInt( 2 ) ) {
        case 1 -> new StringBuffer( 'P' );
        case 2 -> new StringBuffer( 'G' );
        default -> new StringBuffer( 'M' );
      };

    word.append( 'a' );
    word.append( 'i' );
    word.append( 'n' );

    System.out.println( word );
  }
}

Will it output Pain or Main? It will not print Gain as the randon.nextInt(2) will return a value between 0 and 1 both inclusive, never 2.

This example was taken from PUZZLE 23: NO PAIN, NO GAIN in Java™ Puzzlers: Traps, Pitfalls, and Corner Cases.

“The last and most subtle bug is that the expression new StringBuffer('M') probably does not do what you think it does. You may not be familiar with the StringBuffer(char) constructor, and with good reason: It does not exist. There is a parameterless constructor, one that takes a String indicating the initial contents of the string buffer and one that takes an int indicating its initial capacity. In this case, the compiler selects the int constructor, applying a widening primitive conversion to convert the char value 'M' into the int value 77 (JLS 5.1.2). In other words, new StringBuffer('M') returns an empty string buffer with an initial capacity of 77. The remainder of the program appends the characters a, i, and n to the empty string buffer and prints out its contents, which are always ain.”