出现这个Exception in thread "main" java.lang.NoSuchMethodError: main是什么意思？

Question

import java.util.*;
public class Ring
{
private double innerRadius;
private double outerRadius ;
public String color ;
public Ring (double iRadius , double oRadius , String c){
innerRadius = iRadius ;
outerRadius = oRadius;//代码1 //初始化外半径
color = c ;
}
public double getInnerRadius (){
return innerRadius;
}
public double getOuterRadius (){
return outerRadius ;
}
public void setinnerRadius (double iRadius ){
innerRadius = iRadius ;
}public void setOuterRadius (double oRadius ){
outerRadius = oRadius ;
}
public void setColor( String c ){
color=c;//代码3 //设置颜色
}
public double getArea(){
return (outerRadius * outerRadius - innerRadius * innerRadius ) * 3.1415;
}
}
class Example
{
public static void main (String[] args){
Ring ring = new Ring(5,8, "red");
System.out.println("圆环的内半径: " + ring.getInnerRadius());
System.out.println("圆环的外径: " +ring .getOuterRadius());
System.out.println("圆环的颜色: " +ring.color);
System.out.println("圆环的面积: " + ring.getArea()+ "\n");
ring.setOuterRadius (4);
ring.setOuterRadius(6);//代码4 //设置圆环ring 的外半径为6
ring.setColor ("blue");
System.out.println("圆环的内半径: " + ring.getInnerRadius());
System.out.println("圆环的外径: " +ring .getOuterRadius());
System.out.println("圆环的颜色: " +ring.color);
System.out.println("圆环的面积: " + ring.getArea());
}
}

Answer 1

main方法必须定义在public class中，所以出错了，简单的改法就是把Ring类的public去掉，在Example类前加上修饰public

Answer 2

你应该把你的main方法写到Ring类里面

追问

怎么弄呢？我不知道了，，

追答

import java.util.*;
public class Ring
{
private double innerRadius;
private double outerRadius ;
public String color ;
public Ring (double iRadius , double oRadius , String c){
innerRadius = iRadius ;
outerRadius = oRadius;//代码1 //初始化外半径
color = c ;
}
public double getInnerRadius (){
return innerRadius;
}
public double getOuterRadius (){
return outerRadius ;
}
public void setinnerRadius (double iRadius ){
innerRadius = iRadius ;
}public void setOuterRadius (double oRadius ){
outerRadius = oRadius ;
}
public void setColor( String c ){
color=c;//代码3 //设置颜色
}
public double getArea(){
return (outerRadius * outerRadius - innerRadius * innerRadius ) * 3.1415;
}

public static void main (String[] args){
Ring ring = new Ring(5,8, "red");
System.out.println("圆环的内半径: " + ring.getInnerRadius());
System.out.println("圆环的外径: " +ring .getOuterRadius());
System.out.println("圆环的颜色: " +ring.color);
System.out.println("圆环的面积: " + ring.getArea()+ "\n");
ring.setOuterRadius (4);
ring.setOuterRadius(6);//代码4 //设置圆环ring 的外半径为6
ring.setColor ("blue");
System.out.println("圆环的内半径: " + ring.getInnerRadius());
System.out.println("圆环的外径: " +ring .getOuterRadius());
System.out.println("圆环的颜色: " +ring.color);
System.out.println("圆环的面积: " + ring.getArea());
}

}