4-17 定义一个长方形类，定义 求周长和面积的方法，然后定义一个测试类，进行测试。

package ZUOYE;
public class zuoye1 {
	public static void main(String[] args) {
		Rectangle s1 = new Rectangle();
		 	s1.length = 10;
		 	s1.width = 12;
		 	s1.rectangle3();
		 	s1.Perimeter();
		 	s1.Area();
	}
}

class Rectangle {
	 double length;
	 double width;

	public void rectangle3() {
		System.out.println("长方形的长是:" + length + "\t" + "长方形的宽是:" + width);
	}

// 周长

	public double Perimeter () {
		System.out.println("长方形周长是:"+(length+width)*2);
		return(length + width)*2;
	}

// 面积

	public double Area () {
		System.out.println("长方形的面积是:"+(length*width));
		return(length*width);
	}
}