In what scenario would constructors be private or protected?

Question

Is there such a situation where __construct() would be declared anything but public?

If so, why?

score 1 · Accepted Answer · edited May 23 '17 at 11:52

1

A common example for making the constructor private or protected is implementing the singleton pattern. See this answer for a PHP example.

edited May 23 '17 at 11:52

Community

answered Mar 09 '13 at 20:35

molnarm

What would such a design pattern be used for? Forgive me for the "noob" question. – Mar 09 '13 at 20:37
3

@DustinL. see http://stackoverflow.com/questions/4595964/who-needs-singletons/4596323#4596323 – Gordon Mar 09 '13 at 20:39
In other languages, they are used for classes that should have only once instance: resource managers, caches, loggers, etc. – molnarm Mar 09 '13 at 20:40
1

@Gordon Thanks! Love the flowchart as well! :) – Mar 09 '13 at 20:43

score 1 · Answer 2 · answered Oct 20 '15 at 19:00

I also use private constructors when using the builder pattern inside the class, and also when adding static factory methods for a class.

Both can help you to avoid creating too many constructors, and also help you to create constructors with meaningful names. For example instead of:

new Robot(2, 4, 255, 0, 0)

You can create with builder:

RobotBuilder.withNumberOfArms(2).withColor(255,0,0).withNumberOfEyes(2).build()

As the builder is inside the class, only it can call its private constructor.

For static factory methods, you can see that these:

public static Robot createFourArmedRobot();
public static Robot createBlindRobot();

are much more meaningful for an other developer than two constructors with custom parameters. (More relating to OOP than php)

score 0 · Answer 3 · answered Mar 09 '13 at 20:36

0

Usually we do __construct() as private for singleton pattern that is related to design patterns to know more about it visit this page - http://en.wikipedia.org/wiki/Singleton_pattern

answered Mar 09 '13 at 20:36

3 Answers3