延迟加载类本身的事件顺序

Question

If I have this Java class, what exactly is the order of events upon construction/initialization?

class Start {

private Start s = new Start();

public Start(){} //constructor

}

when I call new Start() , isn't there some circular logic being invoked?

Answer 1

Yes, you got yourself a StackOverflowError here, since creating an instance of Start causes another isntance to be created when the s member is initialized, which creates another instance and so on.

private Start s = new Start();

public Start(){}

behaves as :

private Start s;

public Start() {s = new Start();}

To avoid such infinite constructor calls, you can pass an instance of Start to the constructor, or you can initialize the s member by some other method :

private Start s;

public Start(Start s) {this.s = s;}

or

private Start s;

public Start() {}

public initS () {s = new Start();}

Answer 2

A way to lazy set a field is to use a getter. eg

class Start {
    private Start nested = null;

    public Start getNested() {
        return nested == null ? nested = new Start() : nested;
    }
}

This is not thread safe, but avoids infinite loops if used carefully.