/**
* Copyright (C) 2022 by Martin Robillard. See https://codesample.info/about.html
*/
package e2.chapter1;
/**
* Outputs the text of the poem "The Twelve Days of Christmas" to the console.
* This program generates the same output as Ian Phillips' contest-winning
* obfuscated C code (http://www.ioccc.org/1988/phillipps.c), but with a
* self-evident structure that leverages the recursion in the poem.
*/
public class TwelveDays {
public static void (String[] args) {
System.out.(poem());
}
static String[] DAYS = {"first", "second", "third", "fourth",
"fifth", "sixth", "seventh", "eighth",
"ninth", "tenth", "eleventh", "twelfth"};
static String[] GIFTS = {
"a partridge in a pear tree",
"two turtle doves",
"three French Hens",
"four Calling Birds",
"five Golden Rings",
"six Geese a Laying",
"seven Swans a Swimming",
"eight Maids a Milking",
"nine Ladies Dancing",
"ten Lords a Leaping",
"eleven Pipers Piping",
"twelve Drummers Drumming"
};
/*
* Returns the first line in the verse for a given day.
*/
static String firstLine(int )
{
return "On the " + DAYS[day] +
" day of Christmas my true love sent to me:\n";
}
/*
* Returns a string that lists all the gifts received on a given
* day.
*/
static String (int day)
{
if( day == 0 )
{
return "and " + GIFTS[0];
}
else
{
return GIFTS[day] + "\n" + allGifts(day-1);
}
}
/*
* Returns the text of the entire poem.
*/
static String poem()
{
String poem = + "\n\n";
for( int day = 1; day < 12; day++ )
{
poem += firstLine(day) + allGifts(day) + "\n\n";
}
return poem;
}
}This method is intended for the "standard output", i.e., those intended to
a user in a normal flow of events. If you need to print error messages, or
logging/debugging information, you can instead use the "standard error" stream,
with System.err.println.
This method is intended for the "standard output", i.e., those intended to
a user in a normal flow of events. If you need to print error messages, or
logging/debugging information, you can instead use the "standard error" stream,
with System.err.println.
This method is clear because it is short and it abstracts an .
This method is clear because it is short and it abstracts an .
the creation of the first line
the creation of the first line
The only parameterization involved maps directly to the problem domain, the day.
The only parameterization involved maps directly to the problem domain, the day.
To create the list of gifts for a given day, we can leverage the inherent recursion in the poem's structure to organize the code.
To create the list of gifts for a given day, we can leverage the inherent recursion in the poem's structure to organize the code.
This statement shows a typical implementation of a
recursive algorithm. The function creates a list of gifts by
adding the last gift (GIFTS[day]) to a smaller lists of gifts
(allGifts(day-1)).
This statement shows a typical implementation of a
recursive algorithm. The function creates a list of gifts by
adding the last gift (GIFTS[day]) to a smaller lists of gifts
(allGifts(day-1)).
In the first verse, we don't add the conjunction "and" in front of "a partridge". We need to handle this separately.
In the first verse, we don't add the conjunction "and" in front of "a partridge". We need to handle this separately.
No matter how small a program, it can be difficult to completely avoid annoying corner cases.
No matter how small a program, it can be difficult to completely avoid annoying corner cases.
In Java, to print something to the console, you can use the function
System..println(), which is method println() from
the static field out of the System class. In this case, we print
the result of the poem() method to the console.
print(String) and then println().
In Java, to print something to the console, you can use the function
System..println(), which is method println() from
the static field out of the System class. In this case, we print
the result of the poem() method to the console.
print(String) and then println().
x - The String to be printed.
void is a keyword used in place of a return type to indicate that a method does not return a value.
void is a keyword used in place of a return type to indicate that a method does not return a value.
This is the only element that can change from the header declaration of a main method: the name of the parameter can be any valid Java identifier.
This is the only element that can change from the header declaration of a main method: the name of the parameter can be any valid Java identifier.
The main method must have a single parameter, which must be an array of String. The values of this array are supplied when starting the program, typically through the command line. This type can also be expressed as a vararg (variable arguments), written as String....
The main method must have a single parameter, which must be an array of String. The values of this array are supplied when starting the program, typically through the command line. This type can also be expressed as a vararg (variable arguments), written as String....
System class contains several useful class fields and methods. It cannot be instantiated. Among the facilities provided by the System class are standard input, standard output, and error output streams; access to externally defined properties and environment variables; a means of loading files and libraries; and a utility method for quickly copying a portion of an array.
System class contains several useful class fields and methods. It cannot be instantiated. Among the facilities provided by the System class are standard input, standard output, and error output streams; access to externally defined properties and environment variables; a means of loading files and libraries; and a utility method for quickly copying a portion of an array.
Console.charset() if the Console exists, stdout.encoding otherwise.
Console.charset() if the Console exists, stdout.encoding otherwise.
For simple stand-alone Java applications, a typical way to write a line of output data is:
System.out.println(data)
See the println methods in class PrintStream.
String class represents character strings. All string literals in Java programs, such as "abc", are implemented as instances of this class.
String class represents character strings. All string literals in Java programs, such as "abc", are implemented as instances of this class.
Strings are constant; their values cannot be changed after they are created. String buffers support mutable strings. Because String objects are immutable they can be shared. For example:
String str = "abc";
is equivalent to:
char data[] = {'a', 'b', 'c'};
String str = new String(data);
Here are some more examples of how strings can be used:
System.out.println("abc");
String cde = "cde";
System.out.println("abc" + cde);
String c = "abc".substring(2, 3);
String d = cde.substring(1, 2);
The class String includes methods for examining individual characters of the sequence, for comparing strings, for searching strings, for extracting substrings, and for creating a copy of a string with all characters translated to uppercase or to lowercase. Case mapping is based on the Unicode Standard version specified by the Character class.
The Java language provides special support for the string concatenation operator ( + ), and for conversion of other objects to strings. For additional information on string concatenation and conversion, see The Java Language Specification.
Unless otherwise noted, passing a null argument to a constructor or method in this class will cause a NullPointerException to be thrown.
A String represents a string in the UTF-16 format in which supplementary characters are represented by surrogate pairs (see the section Unicode Character Representations in the Character class for more information). Index values refer to char code units, so a supplementary character uses two positions in a String.
The String class provides methods for dealing with Unicode code points (i.e., characters), in addition to those for dealing with Unicode code units (i.e., char values).
Unless otherwise noted, methods for comparing Strings do not take locale into account. The Collator class provides methods for finer-grain, locale-sensitive String comparison.
javac compiler may implement the operator with StringBuffer, StringBuilder, or java.lang.invoke.StringConcatFactory depending on the JDK version. The implementation of string conversion is typically through the method toString, defined by Object and inherited by all classes in Java.