Java - 在其构造函数中实例化同一类的对象

Question

Why instantiating objects of same class within its constructor throws StackOverflowError ? For instance ,

public class A {
    public A () {
        A a = new A() 
    }
}

will throw StackOverFlowError ?

Answer 1

It's exactly the same as with any other function unconditionally calling itself with exactly the same parameters:

public void f() {
  f(); // <---- will cause a stack overflow due to infinite recursion
}

The function just keeps calling itself, and each invocation requires stack space. Sooner or later the stack is exhausted, and you get an exception.

Exactly the same thing happens when A() keeps calling itself (in new A() ).

Answer 2

Because your new A() statement will call the constructor of the A class, which will call the constructor of the A class, and so on. This creates an infinite recursion. THis causes the JVM to throw StackOverflowError s.