JAVA 堆栈溢出

import java.awt.Button;


public class A {
    private Button b ;
    
    public Button getB() {
        return b;
    }

    public void setB(Button b) {
        this.b = b;
    }
    
    A(){
        b = new Button();
        B b = new B(this);
    }
    public static void main(String[] args){
        new A();
    }
}
class B {
    A past = new A();
    B(A p){
        this.past = p;
    }
}

 不太明白 为什么这段代码会报堆栈溢出的错误,,,