public class Ladder {
    double shangdi,xiadi,height,area;
    Ladder(Double shangdi,Double xia,Double gao)
    {
        //使用参数来初始化属性
        //this代表当前类
        this.shangdi=shangdi;
        xiadi=xia;
        height=gao;
    }
    //方法的命名：动词+名次   动词的第一个字母小写 getarea
    //void表示无返回值
    //返回值的类型，要写在方法的前面
    /*public void*/double area(){
        area=(shangdi+xiadi)*height/2;
        System.out.println("梯形的面积是："+area);
        
        //返回语句
        return area;
    }

}

package lianxi;

public class Circle {
    double banjing,zhouchang,area;
    Circle(Double r)
    {
        banjing=r;            
        
    }
        double area(){
        zhouchang=2*Math.PI*banjing;
        area=Math.PI*banjing*banjing;
        System.out.println("圆的周长是："+zhouchang);
        System.out.println("圆的面积是："+area);
        return area;
    }

}

package lianxi;
import lianxi.Ladder;
import lianxi.Circle;
public class A {
    public static void main(String[] args) {
        
        Ladder lader1 =new Ladder(2.0,3.0,6.0);        
        double mj=lader1.area();
        

        Circle circle1=new Circle(3.0);        
        circle1.area();

        }        

}