hellxoul — Thu, 03 Jul 2014 02:48:00 GMT

转自�Q?span style="font-size: 14px;">http://www.cnblogs.com/peida/p/Guava_Ordering.html

Ordering是Guava�c�d��提供的一个犀利强大的比较器工��P��Guava的Ordering和JDK Comparator相比功能更强。它非常�Ҏ��扩展�Q�可以轻松构造复杂的comparator�Q�然后用在容器的比较、排序等操作中�?/p>

　　本质上来��_��Ordering 实例无非��是一个特�D�的Comparator 实例。Ordering只是需要依赖于一个比较器�Q�例如，Collections.max�Q�的�Ҏ��Q��ƈ使其可作为实例方法。另外，Ordering提供了链式方法调用和加强现有的比较器�?/p>

　　下面我们看看Ordering中的一些具体方法和��单的使用实例�?/p>

　　常见的静态方法：

　　natural()�Q?/strong>使用Comparable�c�d��的自焉��序，例如�Q�整��C��到大，字符串是按字兔R��?
　　usingToString() �Q?/strong>使用toString()�q�回的字�W�串按字兔R��序进行排序；
　　arbitrary() �Q?/strong>�q�回一个所有对象的��L��序�Q?即compare(a, b) == 0 ��是 a == b (identity equality)�?本��n的排序是没有��M��含义�Q?但是在VM的生命周期是一个常量�?/p>

　　��单实例：

import java.util.List;
import org.junit.Test;
import com.google.common.collect.Lists;
import com.google.common.collect.Ordering;

public class OrderingTest {

    @Test
    public void testStaticOrdering(){
        List list = Lists.newArrayList();
        list.add("peida");
        list.add("jerry");
        list.add("harry");
        list.add("eva");
        list.add("jhon");
        list.add("neron");
        
        System.out.println("list:"+ list);

        Ordering naturalOrdering = Ordering.natural();        
        Ordering usingToStringOrdering = Ordering.usingToString();
        Ordering arbitraryOrdering = Ordering.arbitrary();
        
        System.out.println("naturalOrdering:"+ naturalOrdering.sortedCopy(list));     
        System.out.println("usingToStringOrdering:"+ usingToStringOrdering.sortedCopy(list));        
        System.out.println("arbitraryOrdering:"+ arbitraryOrdering.sortedCopy(list));
    }
}

　　输出�Q?/p>

list:[peida, jerry, harry, eva, jhon, neron]
naturalOrdering:[eva, harry, jerry, jhon, neron, peida]
usingToStringOrdering:[eva, harry, jerry, jhon, neron, peida]
arbitraryOrdering:[neron, harry, eva, jerry, peida, jhon]

　　操作�Ҏ��Q?/p>

　　reverse(): �q�回与当前Ordering相反的排�?
　　nullsFirst(): �q�回一个将null攑֜�non-null元素之前的Ordering�Q�其他的和原始的Ordering一��P��
　　nullsLast()�Q�返回一个将null攑֜�non-null元素之后的Ordering�Q�其他的和原始的Ordering一��P��
　　compound(Comparator)�Q�返回一个��用Comparator的Ordering�Q�Comparator作�ؓ�W�二排序元素�Q�例如对bug列表�q�行排序�Q�先�Ҏ��bug的��别，再根据优先��q�行排序�Q?br style="margin: 0px; padding: 0px;" />　　lexicographical()�Q�返回一个按照字典元素�P代的Ordering�Q?br style="margin: 0px; padding: 0px;" />　　onResultOf(Function)�Q�将function应用在各个元素上之后, 在��用原始ordering�q�行排序�Q?br style="margin: 0px; padding: 0px;" />　　greatestOf(Iterable iterable, int k)�Q�返回指定的�W�k个可�q�代的最大的元素�Q�按照这个从最大到最��的��序。是不稳定的�?br style="margin: 0px; padding: 0px;" />　　leastOf(Iterable iterable,int k)�Q�返回指定的�W�k个可�q�代的最��的元素�Q�按照这个从最��到最大的��序。是不稳定的�?br style="margin: 0px; padding: 0px;" />　　isOrdered(Iterable)�Q�是否有序，Iterable不能��于2个元素�?br style="margin: 0px; padding: 0px;" />　　isStrictlyOrdered(Iterable)�Q�是否严格有序。请注意�Q�Iterable不能��于两个元素�?br style="margin: 0px; padding: 0px;" />　　sortedCopy(Iterable)�Q�返回指定的元素作�ؓ一个列表的排序副本�?/p>

package com.peidasoft.guava.base;

import java.util.List;

import org.junit.Test;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;
import com.google.common.collect.Ordering;

public class OrderingTest {
    
    @Test
    public void testOrdering(){
        List list = Lists.newArrayList();
        list.add("peida");
        list.add("jerry");
        list.add("harry");
        list.add("eva");
        list.add("jhon");
        list.add("neron");
        
        System.out.println("list:"+ list);
        
        Ordering naturalOrdering = Ordering.natural();
        System.out.println("naturalOrdering:"+ naturalOrdering.sortedCopy(list));    

        List listReduce= Lists.newArrayList();
        for(int i=9;i>0;i--){
            listReduce.add(i);
        }
        
        List listtest= Lists.newArrayList();
        listtest.add(1);
        listtest.add(1);
        listtest.add(1);
        listtest.add(2);
        
        
        Ordering naturalIntReduceOrdering = Ordering.natural();
        
        System.out.println("listtest:"+ listtest);
        System.out.println(naturalIntReduceOrdering.isOrdered(listtest));
        System.out.println(naturalIntReduceOrdering.isStrictlyOrdered(listtest));
        
        
        System.out.println("naturalIntReduceOrdering:"+ naturalIntReduceOrdering.sortedCopy(listReduce));
        System.out.println("listReduce:"+ listReduce);
        
        
        System.out.println(naturalIntReduceOrdering.isOrdered(naturalIntReduceOrdering.sortedCopy(listReduce)));
        System.out.println(naturalIntReduceOrdering.isStrictlyOrdered(naturalIntReduceOrdering.sortedCopy(listReduce)));
        

        Ordering natural = Ordering.natural();
              
        List abc = ImmutableList.of("a", "b", "c");
        System.out.println(natural.isOrdered(abc));
        System.out.println(natural.isStrictlyOrdered(abc));
        
        System.out.println("isOrdered reverse :"+ natural.reverse().isOrdered(abc));
 
        List cba = ImmutableList.of("c", "b", "a");
        System.out.println(natural.isOrdered(cba));
        System.out.println(natural.isStrictlyOrdered(cba));
        System.out.println(cba = natural.sortedCopy(cba));
        
        System.out.println("max:"+natural.max(cba));
        System.out.println("min:"+natural.min(cba));
        
        System.out.println("leastOf:"+natural.leastOf(cba, 2));
        System.out.println("naturalOrdering:"+ naturalOrdering.sortedCopy(list));    
        System.out.println("leastOf list:"+naturalOrdering.leastOf(list, 3));
        System.out.println("greatestOf:"+naturalOrdering.greatestOf(list, 3));
        System.out.println("reverse list :"+ naturalOrdering.reverse().sortedCopy(list));    
        System.out.println("isOrdered list :"+ naturalOrdering.isOrdered(list));
        System.out.println("isOrdered list :"+ naturalOrdering.reverse().isOrdered(list));
        list.add(null);
        System.out.println(" add null list:"+list);
        System.out.println("nullsFirst list :"+ naturalOrdering.nullsFirst().sortedCopy(list));
        System.out.println("nullsLast list :"+ naturalOrdering.nullsLast().sortedCopy(list));
    }

}

//============输出==============
list:[peida, jerry, harry, eva, jhon, neron]
naturalOrdering:[eva, harry, jerry, jhon, neron, peida]
listtest:[1, 1, 1, 2]
true
false
naturalIntReduceOrdering:[1, 2, 3, 4, 5, 6, 7, 8, 9]
listReduce:[9, 8, 7, 6, 5, 4, 3, 2, 1]
true
true
true
true
isOrdered reverse :false
false
false
[a, b, c]
max:c
min:a
leastOf:[a, b]
naturalOrdering:[eva, harry, jerry, jhon, neron, peida]
leastOf list:[eva, harry, jerry]
greatestOf:[peida, neron, jhon]
reverse list :[peida, neron, jhon, jerry, harry, eva]
isOrdered list :false
isOrdered list :false
 add null list:[peida, jerry, harry, eva, jhon, neron, null]
nullsFirst list :[null, eva, harry, jerry, jhon, neron, peida]
nullsLast list :[eva, harry, jerry, jhon, neron, peida, null]

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