ERROR:The applet Tennisball does not have a public constructor Tennisball()

Question

hi all...sorry...i encountered this java error msg with the following code.....n the error msg tat was generated is that i do not have a public constructor which i already have...can some1 please enlighten me..??
import java.applet.*;
import java.awt.*;
public class Tennisball
     double x, y, oldx, oldy, xinc, yinc, v=2.0;
     int i,e,west,north,east,south,ry,rs,score,rx;
     int choice, zone;
     AudioClip ballout;
     boolean running,toggle,enough;
        Color ballcolor;
     Tennis t;
     Color bgColor = Color.black;
     public Tennisball(int w, int n, int e, int s, AudioClip bo)
                west=w;
          east=e;
          south=s;
          north=n;
          ballout = bo;
          //this.t = t;
          xinc=1.7*v;
          yinc=0.7*v;
     public void getRacketPosition(int racket_y)
          ry=racket_y;
          rs=ry;
     public void newBall()
          ballcolor=Color.yellow;
          x=20;
          y=(int)(Math.random()*100+50);
          int angle=(int)(Math.random()*8+1);
          if(angle==1)yinc=-0.7*v;
          if(angle==2)yinc=-0.5*v;
          if(angle==3)yinc=-0.4*v;
          if(angle==4)yinc=-0.3*v;
          if(angle==5)yinc=0.3*v;
          if(angle==6)yinc=0.4*v;
          if(angle==7)yinc=0.5*v;
          if(angle==8)yinc=0.7*v;
          toggle=false;
          running=true;
          enough=false;
          e=0;
     public void move()
          if(running)
               if(!toggle)
                    oldx=x;
                    oldy=y;
                    x+=xinc*v;
                    y+=yinc*v;
               if(x<west && xinc<0)
                    int angle=(int)(Math.random()*8+1);
                    if(angle==1)yinc=-0.7*v;
                    if(angle==2)yinc=-0.5*v;
                    if(angle==3)yinc=-0.4*v;
                    if(angle==4)yinc=-0.3*v;
                    if(angle==5)yinc=0.3*v;
                    if(angle==6)yinc=0.4*v;
                    if(angle==7)yinc=0.5*v;
                    if(angle==8)yinc=0.7*v;
                   xinc=-xinc;
                    t.playClick();
               else if(x>east-10)
                    x=east-10;
                    toggle=true;
                    running=false;
                    score++;
                    t.playBallout();
               else if(y<north || y>south)
                   if(y<north&&yinc<0)
                         yinc=-yinc;
                    if(y>south&&yinc>0)
                         yinc=-yinc;
                    t.playClick();
               else if(x>425 && xinc>0 && y>ry && y<rs+25)
                    if(y<ry+3)zone=1;
                    else if(y>=ry+3&&y<ry+6)zone=2;
                    else if(y>=ry+6&&y<ry+9)zone=3;
                    else if(y>=ry+9&&y<ry+12)zone=4;
                    else if(y>=ry+12&&y<ry+15)zone=5;
                    else if(y>=ry+15&&y<ry+18)zone=6;
                    else if(y>=ry+18&&y<ry+21)zone=7;
                    else if(y>=ry+21)zone=8;
                    if(zone==1)yinc=-0.7*v;
                    if(zone==2)yinc=-0.5*v;
                    if(zone==3)yinc=-0.4*v;
                    if(zone==4)yinc=-0.3*v;
                    if(zone==5)yinc=0.3*v;
                    if(zone==6)yinc=0.4*v;
                    if(zone==7)yinc=0.5*v;
                    if(zone==8)yinc=0.7*v;
                    xinc=-xinc;
                    t.playClick();
     public void toggle()
                    int i=t.j;
                    if(!enough)
                         if(i>-1&&i<11)ballcolor=Color.yellow;
                         if(i>10&&i<20){ballcolor=bgColor;e++;}
                    if (e>35){ballcolor=bgColor;enough=true;}
     public void paint(Graphics g)
          if(toggle)toggle();
          g.setColor(ballcolor);
          g.fillOval((int)x,(int)y,10,10);
}

Answer 1

I thought I should point out a few things
The rule is that every class should have a no
argument constructor that you need to specify
explicitly if you have overloaded the default one.
One of the reaons for that is the following:This is not true, there are many classes that do not have a no argument constructor (For example Integer). Integer is a perfect example of why you would not want a no argument constructor, having an Integer with no value is pointless (theres nothing you can do with it).
public class A {
private final int a ;
public A(int b) {
this.a = b ;
}Now you realize that the variable
n
is getting initialized in the constructor. I see no variable n in the constructor but I take it you mean a
Now if you
refer to
n
somewhere else in you code you get a compile error because
n
might not have been initialized.This is not true, only local variables can cause a
variable (a variable) might not have been initialized
this is because all member fields are initialised with their default valuse. For example all pointers are intitialised to null, ints are intitialised to 0, booleans to false and so on.
>
So you need this:
public class A {
private final int a ;
public A(int b) {
this.a = b ;
public A() {
this(0) ; /* Calls the above constructor with some
default parameter. */
/* You can add some more code below but not above
this(0) */
Of course you know you are never calling the default
constructor but it's still there so you need to
ensure that the variables get initialized if some one
calls it!
As above classes can have no argument constructors
Just add this to your code for example:
public Tennisball() {
this(0, 0, 0, 0, null) ;
} Hope that helped you out!
Thanks,
Nikolas.
PS any duke dollars would be much appreciated as i'm
very poor at the moment :-)I dont mean to be offensive just thought I should clarify these points
Michael