Can I call methods in constructor in Java?

Question

I have situation, where I want to read configuration file only one time, when class is instantiated.

Suppose I have a method named readConfig(), that reads configuration and puts it into a Map object. When the program is required to use configuration value it reads object with it's define key. I want to know that constructor calls only once it's life cycle. Can I put my method readConfig() into constructor, which would give me benefit of one time calling or is there another mechanism to do that?

Answer 1

You can: this is what constructors are for. Also you make it clear that the object is never constructed in an unknown state (without configuration loaded).

You shouldn't: calling instance method in constructor is dangerous because the object is not yet fully initialized (this applies mainly to methods than can be overridden). Also complex processing in constructor is known to have a negative impact on testability.