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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?
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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.
A constructor can call methods, yes. A method can only call a constructor in the same way anything else can: by creating a new instance. Be aware that if a method constructs a new object of the same type, then calling that method from a constructor may result in an infinite loop...
No, you cannot call a constructor from a method. The only place from which you can invoke constructors using “this()” or, “super()” is the first line of another constructor. If you try to invoke constructors explicitly elsewhere, a compile time error will be generated.
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.
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Better design would be
public static YourObject getMyObject(File configFile){ //process and create an object configure it and return it } If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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