第一個過程程的mapreduce函式：

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.StringTokenizer;


public class MapReduce extends MapperReduce{

	public MapReduce(){
		super();
	}
	
	public void printf(List<String> list1,List<String> list2) throws IOException{
		if((!list1.isEmpty()) && (!list2.isEmpty())){
			Iterator<String> Iter1=list1.iterator();
			while(Iter1.hasNext()){
				String tmp1=Iter1.next();
				Iterator<String> Iter2=list2.iterator();
				while(Iter2.hasNext()){
					String tmp2=Iter2.next();
					WriteReducer(tmp1,tmp2);
				}
			}
		}
	}
	
	//map函式開始
		public void Mapper(String key,String value) throws IOException{
			//key為行偏移量，value為每一行的值
			String[] count=value.split(" ");
			if(!count[1].trim().equals("")){
				WriteMaper(count[1].trim(),count[0].trim()+" "+"1");
				WriteMaper(count[1].trim(),count[0].trim()+" "+"2");
			}
		}
	//map函式結束
		
	//reduce函式開始	
		public void Reducer(String key,Iterator<String> value) throws IOException{
			List<String> list1=new ArrayList<String>();
			List<String> list2=new ArrayList<String>();
			while(value.hasNext()){
				String tmp=value.next();
				String[] tmp1=tmp.split(" ");
				if(tmp1[1].equals("1")){
					list1.add(tmp1[0]);
				}else{
					list2.add(tmp1[0]);
				}
			}
			printf(list1,list2);
		}
	//reduce函式結束
	public static void main(String[] args) throws IOException {
		MapReduce a=new MapReduce();
		a.IterMapper();
		a.IterReducer();
	}
}
 

本程式例項是：單表自連線，連線欄位是 user

star1 user1
star2 user1
star3 user1
star3 user2

輸出：

star1 star1
star1 star2
star1 star3
star2 star1
star2 star2
star2 star3
star3 star1
star3 star2
star3 star3
star3 star3

第二個過程程的mapreduce函式：

import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;


public class MapReduce extends MapperReduce{

	public MapReduce(){
		super();
	}
	
	
	//map函式開始
		public void Mapper(String key,String value) throws IOException{
			String[] content=value.split(" ");
			WriteMaper(content[0],content[1]);
		}
	//map函式結束
		
	//reduce函式開始	
		public void Reducer(String key,Iterator<String> value) throws IOException{
			List<String> list=new ArrayList<String>();
			while(value.hasNext()){
				list.add(value.next());
			}
			Set<String> set = new HashSet<String>(list);
			Map<String,Integer> map=new HashMap<String,Integer>();
			Iterator<String> IterSet=set.iterator();
			while(IterSet.hasNext()){
				map.put(IterSet.next(),0);
			}
			for(int i=0;i<list.size();i++){
				map.put(list.get(i),map.get(list.get(i))+1);
			}
			Iterator<String> It = map.keySet().iterator();
			while(It.hasNext())
			{   
				String tmp=It.next();
				if(!tmp.equals(key)){
					WriteReducer(key,tmp+" "+String.valueOf(((float)map.get(tmp))/map.get(key)));
				}
			    }
		}
	//reduce函式結束
	public static void main(String[] args) throws IOException {
		MapReduce a=new MapReduce();
		a.IterMapper();
		a.IterReducer();
	}
}
 

輸入：

star1 star1star1 star2star1 star3star2 star1star2 star2star2 star3star3 star1star3 star2star3 star3star3 star3

輸出：

star1 star2 1.0

star1 star3 1.0

star2 star1 1.0

star2 star3 1.0

star3 star1 0.5

star3 star2 0.5