Question

My questions is this:

Why can I not pass this to an explicit call to a constructor?

Example:

class MyClass {

    MyClass x;

    public MyClass(MyClass c) {
        x = c;
    }

    public MyClass() {
        this(this);        // Error
    }
}

Answer 1

You are trying to pass a reference to this from a constructor to another constructor on the same instance.

In Java you cannot access this implicitly or explicitly in the constructor before returning from an implicit or explicit call to this() or super(). This is because the super class has not yet initialised.

You may need to duplicate code in the constructor:

class MyClass {
    private final MyClass myInstance;
    public MyClass(MyClass myInstance) {
        this.myInstance = myInstance;
    }
    public MyClass() {
        this.myInstance = this;
    }
}

There may be ways to hack around it using a private constructor, but then you are into hacking territory.