用lang里面的，要重写好多方法。直接在下面重写类算了

应该是这样实现吧。。

package cn.tedu.basic;



public class Demo_FindMax {
	/** * Return max item in arr * Precondition:arr.length>0 * @param arr * @return */
	public static Comparable findMax(Comparable[] arr) {
		int maxIndex = 0 ; 
		for(int i=1 ; i<arr.length ; i++) {
			if(arr[i].compareTo(arr[maxIndex])>0) {
				maxIndex = i ;
			}
		}
		return arr[maxIndex] ; 
	}
	
	/** * Test findMax on Shape and String objects. * @param args */
	public static void main(String[] args) {
		String[] st1 = {
			"123",
			"222",
			"a33",
			"1"
		};
		System.out.println(findMax(st1));
		
		Shape[] sh1 = {
				new Circle(2.0),
				new Shape(3.0),
				new Rectangle(3.0 , 4.0)
		};
		System.out.println(findMax(sh1).getClass());
	}
}

class Shape implements Comparable{ //形状
	double area;
	public Shape(double area){
		this.area = area;
	}
	@Override
	public int compareTo(Object o) {
		Shape anotherShape = (Shape) o;		
		return (int) (this.area - anotherShape.area);
	}
}

class Circle extends Shape{ //圆形
	public Circle(double r) {
		super(r*r*Math.PI);
	}
}


class Rectangle extends Shape{//矩形

	public Rectangle(double l , double w ) {
		super(l*w);
		// TODO Auto-generated constructor stub
	} 
	
}