I'm relatively new to Java and I'm coding extensions/plugins for online game Minecraft.
I've recently started "bigger" projects which require more classes to preserve neatness. I am still trying to fully understand how constructors work, but most recent try resulted into Stack Overflow (one constructor calling another, in loop).
In my case, for example, I have two classes, Main and MySQL.
Main class initializes plugin, MySQL class contacts database and returns data to any class which calls it.
Example problematic code:
Main.java
class Main extends JavaPlugin {
private final MySQL mysql = new MySQL();
//Method which is called first
void onEnable(){
//Just an example of initializing
mysql.init();
mysql.open();
}
}
MySQL.java
class MySQL {
private final Main main = new Main();
void init(){}
void open(){}
}
I know what the problem is, I just don't know proper solution, which would work with even more classes.
Also if I would have another class, main would connect to MySQL, another class would communicate with it, I should do something like main.mysql.method ?
Simplified, easy to understand explanation on how constructors and instances ("new" keyword) work would be much appreciated. Thanks in advance !
First of all, just as a pointer for future applications, you might want to take a look at Design Patterns, they tend to make design cleaner and easier to maintain.
In your case you have created a Circular Reference. The easiest way to get around it would be to make something like so:
class Main extends JavaPlugin {
private final MySQL mysql;
public Main(MySQL mysql)
{
this.mysql = mysql
}
//Class which is called first
void onEnable() {
//Just an example of initializing
mysql.init();
mysql.open();
}
}
class MySQL {
private final Main main = new Main(this);
void init(){}
void open(){}
}
This should solve the problem.
That being said, I am assuming that the MySQL class will have database related mechanisms. Such mechanisms are usually exposed through a Singleton design pattern. This design pattern should allow you to access the methods within the MySQL class only when you need them, thus also avoiding the circular reference issue.