java - 了解 javap 输出

Question

我有一个非常简单的类(class):

package MyDev;

public class Point3D  {

   public Point3D(){x = 0; y = 0;z = 0;}

   public float x, y, z;
   public Point3D( float X, float Y, float Z ) 
   {
      x = X;  y = Y;  z = Z;
   }
}

当我在这个类上运行javap -c时，这就是我得到的:

C:\Projects\Development\MyJava\bin\MyDev>"C:\Program Files (x86)\Java\jdk1.7.0_55\bin\javap" -c Point3D.class
Compiled from "Point3D.java"
public class MyDev.Point3D {
  public float x;

  public float y;

  public float z;

  public MyDev.Point3D();
    Code:
       0: aload_0
       1: invokespecial #12                 // Method java/lang/Object."<init>":()V
       4: aload_0
       5: fconst_0
       6: putfield      #14                 // Field x:F
       9: aload_0
      10: fconst_0
      11: putfield      #16                 // Field y:F
      14: aload_0
      15: fconst_0
      16: putfield      #18                 // Field z:F
      19: return

  public MyDev.Point3D(float, float, float);
    Code:
       0: aload_0
       1: invokespecial #12                 // Method java/lang/Object."<init>":()V
       4: aload_0
       5: fload_1
       6: putfield      #14                 // Field x:F
       9: aload_0
      10: fload_2
      11: putfield      #16                 // Field y:F
      14: aload_0
      15: fload_3
      16: putfield      #18                 // Field z:F
      19: return
}

为什么？ 为什么第二个构造函数也有签名 ()V，而不是 (FFF)V ？我一生都无法理解这一点!

Answer 1

这是对Object构造函数的调用。对父类(super class)构造函数的调用始终是构造函数中发生的第一件事。