定义一个矩形类Rectangle： [必做题] 2.1 定义三个方法：getArea()求面积、getPer()求周长，showAll()分别在控制台输出长、宽、面积、周长。 2.2 有2个属性：

package changfangxing;

	public class Rectangle{
		double length;
		double width;
		public Rectangle(int width,int length){
			this.length=length;
			this.width=width;
}
		public double getArea(int length,int width){
			return this.length*this.width;
}
		public double getPer(int length,int width){
			return 2*(this.length+this.width);
}
		public void showAll(){
			System.out.println("长"+this.length+","+this.width);
			System.out.println("面积是"+this.length*this.width);
			System.out.println("周长是"+2*(this.length+this.width));
		}	
}

package changfangxing;

public class Test {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Rectangle r=new Rectangle(2,4);
		r.showAll();
	}

}