定义一个矩形类Rectangle、梯形类Ladder、测试类AreaTest，这三个类处于同一个包com.test中，AreaTest类为主类，在main()方法中创建矩形类和梯形类的相应对象，调用其成员函数计算矩形、梯形的面积

Rectangle类：

package com.test;

public class Rectangle {
    private double length;
    private double width;

    public Rectangle(double length, double width) {
        this.length = length;
        this.width = width;
    }

    public double getLength() {
        return length;
    }

    public void setLength(double length) {
        this.length = length;
    }

    public double getWidth() {
        return width;
    }

    public void setWidth(double width) {
        this.width = width;
    }

    public double getArea() {
        return length * width;
    }
}

Ladder类：

package com.test;

public class Ladder {
    private double upperWidth;
    private double lowerWidth;
    private double height;

    public Ladder(double upperWidth, double lowerWidth, double height) {
        this.upperWidth = upperWidth;
        this.lowerWidth = lowerWidth;
        this.height = height;
    }

    public double getUpperWidth() {
        return upperWidth;
    }

    public void setUpperWidth(double upperWidth) {
        this.upperWidth = upperWidth;
    }

    public double getLowerWidth() {
        return lowerWidth;
    }

    public void setLowerWidth(double lowerWidth) {
        this.lowerWidth = lowerWidth;
    }

    public double getHeight() {
        return height;
    }

    public void setHeight(double height) {
        this.height = height;
    }

    public double getArea() {
        return (upperWidth + lowerWidth) * height / 2;
    }
}

AreaTest类：

package com.test;

public class AreaTest {
    public static void main(String[] args) {
        Rectangle rectangle = new Rectangle(5, 10);
        Ladder ladder = new Ladder(5, 10, 8);

        System.out.println("矩形的面积为：" + rectangle.getArea());
        System.out.println("梯形的面积为：" + ladder.getArea());
    }
}