Question

Java程序报错，对着课本上敲得报错Lader cannot be resolved to a type

package MyFirst;

import java.util.Scanner;
import java.util.logging.Logger;

public class compute {
public static void main(String args[]){
double area=0;
Lader laderOne;这里报错Lader cannot be resolved to a type
laderOne=new Lader();这里也是Lader cannot be resolved to a type
laderOne.seAbove(10);
laderOne.setBottom(20);
laderOne.setHeight(30);
area=laderOne.computeArea();
class Lader{
double above,bottom,height;
Lader(){}
Lader(double a,double b,double c){
above=a;
bottom=b;
height=c;
}
public void setAbove(double a){
above=a;

}
public void setBottom(double b){
bottom=b;

}
public void setHeight(double c){

height=c;

}
double computeArea(){
return(above+bottom)*height/2.0;
}
}

System.out.printf("该面积是："+area);
}

}

Answer 1

package MyFirst;
public class compute
{
    public static void main(String args[])
    {
        class Lader
        {
            double above, bottom, height;
            Lader()
            {
            }
            @SuppressWarnings("unused")
            Lader(double a, double b, double c)
            {
                above = a;
                bottom = b;
                height = c;
            }
            public void setAbove(double a)
            {
                above = a;
            }
            public void setBottom(double b)
            {
                bottom = b;
            }
            public void setHeight(double c)
            {
                height = c;
            }
            double computeArea()
            {
                return (above + bottom) * height / 2.0;
            }
        }
        double area = 0;
        Lader laderOne;
        laderOne = new Lader();
        laderOne.setAbove(10);
        laderOne.setBottom(20);
        laderOne.setHeight(30);
        area = laderOne.computeArea();
        System.out.printf("该面积是：" + area);
    }
}

另外，包名建议小写，类名建议首字母大写。

Answer 2

Lader不是系统默认的类，而是一个自定义个实体类。

所以你应该这样做：
1、新创建一个叫做Lader的类。
2、在你现在这个java文件中到入新创建的类的包。
这样就好了。