List 分组实现

Posted 2022-11-21 Luther-

List 分组实现

首先创建实体类

import java.io.Serializable;

public class Foo implements Serializable
	
	private static final long serialVersionUID = 1395253695450566358L;
	
	private String code;
	private String name;
	
	public String getCode() 
		return code;
	
	public void setCode(String code) 
		this.code = code;
	
	public String getName() 
		return name;
	
	public void setName(String name) 
		this.name = name;
	
	
	@Override
	public String toString() 
		return "[code=" + code + ", name=" + name + "]";
	
	
	
	

写工具类

创建排序规则接口（按照什么条件排序）

public interface GroupBy <T>
	
	T groupby(Object obj);

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

public class Util 
	
	@SuppressWarnings("unchecked")
	public static <K extends Comparable<K>, V> Map<K, Collection<V>> group(Collection<V> colls, GroupBy<?> gb)
		
		if(colls == null || colls.isEmpty())
			return null;
		
		
		if(gb == null)
			return null;
		
		
		Iterator<V> iter = colls.iterator();
		Map<K,Collection<V>> map = new HashMap<K, Collection<V>>();
		while(iter.hasNext())
			V v = iter.next();
			K k = (K) gb.groupby(v);
			if(map.containsKey(k))
				map.get(k).add(v);
			else
				ArrayList<V> list = new ArrayList<V>();
				list.add(v);
				map.put(k, list);
			
		
		
		return map;
		
	
	
	public static void main(String[] args) 
		ArrayList<Foo> list = new ArrayList<Foo>();
		Foo foo1 = new Foo("001","abc1");
		list.add(foo1);
		Foo foo2 = new Foo("001","abc2");
		list.add(foo2);
		Foo foo3 = new Foo("002","abc3");
		list.add(foo3);
		Foo foo4 = new Foo("002","abc4");
		list.add(foo4);
		Foo foo5 = new Foo("003","abc5");
		list.add(foo5);
		Foo foo6 = new Foo("004","abc6");
		list.add(foo6);
		
		Map<String, Collection<Foo>> map = Util.group(list, new GroupBy<String>()

			public String groupby(Object obj) 
				Foo foo = (Foo) obj;
				return foo.getCode();
						
		);
		
		System.out.println(map.toString());
	

输出结果

004=[[code=004, name=abc6]], 001=[[code=001, name=abc1], [code=001, name=abc2]], 002=[[code=002, name=abc3], [code=002, name=abc4]], 003=[[code=003, name=abc5]]