类中定义成员方法。加不加public有什么区别？

  1 class Trangle{
  2     double sideA, sideB, sideC, area, length;
  3     boolean flag;
  4     Trangle(double a, double b, double c){//public
  5         if(a < (b + c) && b < (a + c) && c < (a + b)){
  6             sideA = a;
  7             sideB = b;
  8             sideC = c;
  9             flag = true;
 10         }
 11         else
 12             flag = false;
 13     }
 14     double getLength(){//public
 15         length = sideA + sideB + sideC;
 16         return length;
 17     }
 18     double getArea(){//public
 19         if(flag){
 20             double p = (sideA + sideB + sideC)/2.0;
 21             area = Math.sqrt(p*(p-sideA)*(p-sideB)*(p-sideC));
 22             return area;
 23         }
 24         else{
 25             System.out.println("This is not a trangle");
 26             return 0;
 27         }
 28     }
 29     void setABC(double a, double b, double c){//public
 30         if(a < (b + c) && b < (a + c) && c < (a + b)){
 31             sideA = a;
 32             sideB = b;
 33             sideC = c;
 34             flag = true;
 35         }
 36         else{
 37             flag = false;
 38             sideA = sideB =sideC = 0;        
 39         }
 40     }    
 41 }
 42 
 43 class Lader{
 44     double above,botton,height,area;
 45     Lader(double a,double b, double h){
 46         above =a;
 47         botton = b;
 48         height = h;
 49     }
 50     public double getArea(){
 51         area = (above + botton)*height/2.0;
 52         return area;
 53     }
 54 }
 55 
 56 class Circle{
 57     double radius, area;
 58     Circle(double r){
 59         if(r > 0)
 60             radius = r;
 61         else 
 62             radius = 0;
 63     }
 64     double getRadius(){
 65         return radius;
 66     }
 67     double getArea(){
 68         area = Math.PI * radius * radius;
 69         return area;
 70     }
 71     double getLength(){
 72         return 2 * Math.PI * radius;
 73     }
 74     void setRadius(double r){
 75         if(r > 0)
 76             radius = r;
 77         else 
 78             radius = 0;
 79     }
 80 }
 81 
 82 public class AreaAndLength{
 83     public static void main(String[] args){
 84         double length, area;
 85         Circle circle = null;
 86         Trangle trangle = null;
 87         Lader lader = null;
 88         circle = new Circle(2.0);
 89         trangle = new Trangle(5.0, 3.0, 4.0);
 90         lader = new Lader(4, 8, 5);
 91         
 92         length = circle.getLength();
 93         System.out.print("
Circle's length is "+ length);    
 94         area = circle.getArea();
 95         System.out.println(". Area is "+ area +".
");
 96         
 97         length = trangle.getLength();
 98         System.out.print("Trangle's length is "+ length);    
 99         area = trangle.getArea();
100         System.out.println(". Area is "+ area +".
");
101         
102         area = lader.getArea();
103         System.out.println("Lader's area is "+ area +".
");
104         
105         trangle.setABC(12, 34, 1);
106         area = trangle.getArea();
107         System.out.print("This nwe trangle's area is "+ area);
108         length = trangle.getLength();
109         System.out.println(". Length is "+ length +".
");    
110     }
111 }
trangle类的成员函数加不加public都可以运行成功，什么原因呢？