Java构造器调用疑问：为何super相关代码执行情况存在差异？

疑问一：GoldenDelicious无参构造器的打印语句为何未执行？ #

提供的Test类代码如下：

public class Test {
  public static void main(String[] args) {
    Apple a = new Apple();
    System.out.println(a);
    System.out.println("---------------");
    
    GoldenDelicious g = new GoldenDelicious(7);
    System.out.println(g);
    System.out.println("---------------");

    Apple c = new GoldenDelicious(8);
    System.out.println(c);
  }
}

class Apple {
  double weight;
  
  public Apple() {
    this(1);
    System.out.println("Apple no-arg constructor");
  }
  
  public Apple(double weight) {
    this.weight = weight;
    System.out.println("Apple constructor with weight");
  }
  
  @Override 
  public String toString() {
    return "Apple: " + weight;
  }
}
class GoldenDelicious extends Apple {
  public GoldenDelicious() {
    this(5);
    System.out.println("GoldenDelicious non-arg constructor");
  }
  
  public GoldenDelicious(double weight) {
    super(weight);
    this.weight = weight;
    System.out.println("GoldenDelicious constructor with weight");
  }
  
  @Override 
  public String toString() {
    return "GoldenDelicious: " + weight;
  }
}

代码输出：

Apple constructor with weight Apple no-arg constructor Apple: 1.0
--------------- Apple constructor with weight GoldenDelicious constructor with weight GoldenDelicious: 7.0
--------------- Apple constructor with weight GoldenDelicious constructor with weight GoldenDelicious: 8.0

核心原因：main方法里从未调用过GoldenDelicious的无参构造器。所有创建GoldenDelicious实例的代码，都是调用带double参数的构造器（new GoldenDelicious(7)、new GoldenDelicious(8)）。只有执行new GoldenDelicious()时，这个无参构造器才会被触发，进而执行里面的打印语句。

额外补充：就算调用了无参构造器，它第一行的this(5)会先调用本类的带参构造器，等带参构造器逻辑执行完毕后，才会回到无参构造器执行那行打印语句。

疑问二：调用super(color, filled);父类构造器后，子类构造器的后续代码为何还能执行？ #

Circle类的关键构造器代码：

public Circle(double radius, String color, boolean filled) {
    super(color, filled);
    this.radius = radius;
    System.out.println("does this print?");
}

Java构造器的执行规则是：子类构造器必须先完成父类的初始化（显式调用super()或隐式调用父类无参构造器），但父类构造器执行完毕后，会回到子类构造器继续执行剩余代码。

super(color, filled)仅负责调用父类GeometricObject的对应构造器，完成父类成员的初始化工作。这一步完成后，程序会回到当前的Circle构造器，继续执行this.radius = radius;和打印语句等子类自身的构造逻辑，所以那行打印语句会正常执行。

内容的提问来源于stack exchange，提问作者Linh Tran