通过JAVA集合求和

需求：
从数据库取出表的List对象，通过判断List<bean>的主键判断该List是否有相同的属性值，如果有相同属性值，其他的数值叠加。做了个demo。
bean：

package com.bean;

public class bean {
	private String type;
	private Integer num;
	public String getType() {
		return type;
	}
	public void setType(String type) {
		this.type = type;
	}
	public Integer getNum() {
		return num;
	}
	public void setNum(Integer num) {
		this.num = num;
	}
	
}

实现类：

package com.main;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import com.bean.bean;

public class Main {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		List<bean> list = new ArrayList<bean>();

		bean demobean6 = new bean();
		demobean6.setType("type3");
		demobean6.setNum(10);

		list.add(demobean6);

		bean demobean = new bean();
		demobean.setType("type1");
		demobean.setNum(2);

		list.add(demobean);

		bean demobean5 = new bean();
		demobean5.setType("type3");
		demobean5.setNum(10);

		list.add(demobean5);

		bean demobean2 = new bean();
		demobean2.setType("type1");
		demobean2.setNum(30);

		list.add(demobean2);

		bean demobean3 = new bean();
		demobean3.setType("type1");
		demobean3.setNum(10);

		list.add(demobean3);

		bean demobean4 = new bean();
		demobean4.setType("type2");
		demobean4.setNum(10);

		list.add(demobean4);

		bean demobean7 = new bean();
		demobean7.setType("type8");
		demobean7.setNum(1090);

		list.add(demobean7);

		/*
		 * 数据结构可以考虑用Map,因为Map相同key值只能有一个,当有相同key值对象put进来时,Map会擦写掉原对象. 实现类似group
		 * by的功能.
		 */
		Map<String, Integer> result = new HashMap<String, Integer>();

		sort: for (bean item : list) {
			if (result.get(item.getType()) == null) {
				result.put(item.getType(), item.getNum());// 如果没有此类型,则添加此类型的数值
				continue sort;
			}
			// 如果有此类型,则把此类型的数值修改为-->原来的数值+新数值,实现类似sum功能
			result.put(item.getType(), item.getNum()
					+ result.get(item.getType()));
		}

		for (String key : result.keySet()) {
			System.out.println(key + " : " + result.get(key));
		}

	}

}