Editing Quine (computing) (section)

===Constructive quines===
In general, the method used to create a quine in any programming language is to have, within the program, two pieces: (a)&nbsp;[[Source code|code]] used to do the actual printing and (b)&nbsp;[[data]] that represents the textual form of the code.  The code functions by using the data to print the code (which makes sense since the data represents the textual form of the code), but it also uses the data, processed in a simple way, to print the textual representation of the data itself.

Here are three small examples in Python3:
<syntaxhighlight lang="python3">
# Example A. chr(39) == "'".
a = 'a = {}{}{}; print(a.format(chr(39), a, chr(39)))'; print(a.format(chr(39), a, chr(39)))
</syntaxhighlight>
<syntaxhighlight lang="python3">
# Example B. chr(39) == "'".
b = 'b = %s%s%s; print(b %% (chr(39), b, chr(39)))'; print(b % (chr(39), b, chr(39)))
</syntaxhighlight>
<syntaxhighlight lang="python3">
# Example C. %r will quote automatically.
c = 'c = %r; print(c %% c)'; print(c % c)
</syntaxhighlight>The following [[Java (programming language)|Java]] code demonstrates the basic structure of a quine.
<syntaxhighlight lang="java">
public class Quine
{
  public static void main(String[] args)
  {
    char q = 34;      // Quotation mark character
    String[] l = {    // Array of source code
    "public class Quine",
    "{",
    "  public static void main(String[] args)",
    "  {",
    "    char q = 34;      // Quotation mark character",
    "    String[] l = {    // Array of source code",
    "    ",
    "    };",
    "    for (int i = 0; i < 6; i++)           // Print opening code",
    "        System.out.println(l[i]);",
    "    for (int i = 0; i < l.length; i++)    // Print string array",
    "        System.out.println(l[6] + q + l[i] + q + ',');",
    "    for (int i = 7; i < l.length; i++)    // Print this code",
    "        System.out.println(l[i]);",
    "  }",
    "}",
    };
    for (int i = 0; i < 6; i++)           // Print opening code
        System.out.println(l[i]);
    for (int i = 0; i < l.length; i++)    // Print string array
        System.out.println(l[6] + q + l[i] + q + ',');
    for (int i = 7; i < l.length; i++)    // Print this code
        System.out.println(l[i]);
  }
}</syntaxhighlight>
The source code contains a string array of itself, which is output twice, once inside quotation marks.

This code was adapted from an original post from c2.com, where the author, Jason Wilson, posted it as a minimalistic version of a Quine, without Java comments.<ref>{{cite web |url=http://wiki.c2.com/?QuineProgram |title=Quine Program |website=wiki.c2.com}}</ref>

Thanks to new [https://openjdk.java.net/jeps/378 text blocks] feature in Java 15 (or newer), a more readable and simpler version is possible:<ref>{{Cite web|url=https://gist.github.com/destan/c0db5a237e9875a56141403aaa6cb9c7|title=Simple Java quine, self replicating (Self copying) Java code, with text blocks. This code can be run with Java 15+ or Java 13+ with special flags. License is public domain, no rights reserved}}</ref>

<syntaxhighlight lang="java">
public class Quine {
	public static void main(String[] args) {
		String textBlockQuotes = new String(new char[]{'"', '"', '"'});
		char newLine = 10;
		String source = """
public class Quine {
	public static void main(String[] args) {
		String textBlockQuotes = new String(new char[]{'"', '"', '"'});
		char newLine = 10;
		String source = %s;
		System.out.print(source.formatted(textBlockQuotes + newLine + source + textBlockQuotes));
	}
}
""";
		System.out.print(source.formatted(textBlockQuotes + newLine + source + textBlockQuotes));
	}
}
</syntaxhighlight>The same idea is used in the following [[SQL]] quine:<syntaxhighlight lang="sql">
SELECT REPLACE(REPLACE('SELECT REPLACE(REPLACE("$",CHAR(34),CHAR(39)),CHAR(36),"$") AS Quine',CHAR(34),CHAR(39)),CHAR(36),'SELECT REPLACE(REPLACE("$",CHAR(34),CHAR(39)),CHAR(36),"$") AS Quine') AS Quine

</syntaxhighlight>