泛型的学习应用

package com.easyway.commons.ispace.dev.advances.generics;

import java.io.Serializable;
import java.lang.reflect.Array;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;

import org.apache.commons.lang.ArrayUtils;
/**
 * 
 * 泛型的学习应用
 * @author longgangbai
 * @date 2010-5-6
 * @version 1.0
 * @since JDK6.0
 */
public class ArrayAlg {
	
	
	public static void minmaxBonus(Number[] a ,Pair<? super Number > result)
	{
		
	}
	
	public static void printBuddies(Pair<? extends Pair> pair){
		
	}
	
	
	public static <T> boolean hasNulls(Pair<?> pair){
		 return pair.getFirst()==null||pair.getSecond()==null;
	}
	@SuppressWarnings("unchecked")
	public static <T extends Comparable<? super T>> Pair<T> minmax(T[] arr)
	{
		T[] data=(T[])Array.newInstance(arr.getClass().getComponentType(),2);
		
		if(ArrayUtils.isEmpty(arr))
		{
			 return null;
		}
		data[0]=arr[0];
		data[1]=arr[0];
		for (int i = 0; i < arr.length; i++) {
			if(data[0].compareTo(arr[i])>0){
				data[0]=arr[i];
			}
			if(data[1].compareTo(arr[i])<0){
				data[1]=arr[i];
			}
		}
		return new Pair<T>(data[1],data[0]);
	}
	/**
	 * 由索引获得
	 * @param <T>
	 * @param <U>
	 * @param a
	 * @param b
	 * @return
	 */
	public static <T,U> T getByIdx(T[] a,U b){
		 int h=b.hashCode();
		 h^=(h>>>20)^(h>>>12);
		 h=h^(h>>>7)^(h>>>4);
		 int index=h&(a.length-1);
		  return a[index];
	}
	//这个就是在普通类 ArrayAlg 中定义的泛型方法 
	public static <T> T getMiddle(T[] a){ 
		return a[a.length/2]; 
	} 
	
	@SuppressWarnings("unchecked")
	public static <T extends Comparable&Serializable> T min(T... a)
	{
		  if(a==null||a.length==0){
			   return null;
		  }
		  T min=a[0];
		  for (int i = 0; i < a.length; i++) {
			if(min.compareTo(a[i])>0){
				min=a[i];
			}
		  }
		  return min;
	}
	public static String getMiddleStr(String[] a){ 
		return "Not Generic Method."; 
	} 
	
	class Interval<T extends Comparable&Serializable> implements Serializable
	{
		private T lower;
		
		private T upper;
		public Interval(T first ,T second){
			 if(first.compareTo(second)<=0){
				 lower=first;
				 upper=second;
			 }
		}
	}
	
	public static <T>  Pair<T> makePair(Class<T> clazz){
		 try {
			return new Pair<T>(clazz.newInstance(),clazz.newInstance());
		} catch (Exception e) {
           return null;
		}
	}
	
	
	
	public static <T extends Throwable> void doWork(T t)throws T
	{
		try {
			System.out.println(" generics Throwable ....");
			
		} catch (Throwable cause) {
			System.out.println(cause.getMessage());
			t.initCause(cause);
			 throw  t;
		}
	}


	public static void main(String[] args) { 
		String[] words={"Mary","had","a","little","lamb"};
		Pair<String>  mm=ArrayAlg.minmax(words);
		System.out.println(" min ="+mm.getFirst());
		System.out.println(" max ="+mm.getSecond());
		
		
		
		
		String[] names = {"Fantasia","Unmi","Kypfos"}; 
		//上面那样写是可以，编译器可推断出要调用的方法，所以省去<String> 
		String middle = ArrayAlg.<String>getMiddle(names);    //Not Generic Method.
		System.out.println(middle);    
		
	    double mindouble=ArrayAlg.<Double>getMiddle(new Double[]{3.14,1745.0,6.0});
		System.out.println("mindouble ="+mindouble);
		
		String[] snames = {"Fantasia","Kypfos","Unmi"}; 
		//显式的用 <String, Object> 去调用定义的泛型方法 
		String name = ArrayAlg.<String, Date>getByIdx(snames,new Date()); 
		//隐式调用泛型方法 
		String name1 = ArrayAlg.getByIdx(names,"GameOver");  
		//会输出 Unmi:Fantasia，或 Fantasia:Fantasia 
		System.out.println(name + ":" + name1); 
		
		GregorianCalendar[] birthdays=
		{
				 new GregorianCalendar(1906,Calendar.DECEMBER,9),
				 new GregorianCalendar(1815,Calendar.DECEMBER,10),
				 new GregorianCalendar(1903,Calendar.DECEMBER,3),
				 new GregorianCalendar(1910,Calendar.JULY,22)
		};
		
		Pair<GregorianCalendar> arrayalg=ArrayAlg.<GregorianCalendar>minmax(birthdays);
		System.out.println(" min ="+mm.getFirst());
		System.out.println(" min ="+mm.getFirst());
		
		
		
		
	} 

}