工具类——自定义Collections集合方法

package com.test.util;

import java.util.Collection;

import org.apache.commons.collections.CollectionUtils;

/**
 * 自定义集合处理类
 * @author : shijing
 * 2017年5月18日下午2:00:10
 */
public class CollectionsCustom {

	
	/**
     * 将传入的collection内对象进行计算后得出结果
      * @author : shijing  
      * 2017年5月18日下午3:09:53
     * @param original       计算前collection
     * @param reduceFunction 计算方式
     * @param initValue      计算结果初始值
     * @param <Input>        collection对象类型
     * @param <Output>       结果类型
     * @return
     */
    public static <Input, Output> Output reduce(Collection<Input> original, Output initValue, ReduceFunction<Input, Output> reduceFunction) {
        Output result = initValue;
        if (CollectionUtils.isEmpty(original)) {
            return result;
        }
        if (reduceFunction == null) {
            return result;
        }
        for (Input input : original) {
            result = reduceFunction.apply(input, result);
        }
        return result;
    }
    
    /**
     * 自定义计算接口
     * @author : shijing
     * 2017年5月18日下午3:09:53
     * @param <Input>
     * @param <Result>
     */
    public interface ReduceFunction<Input, Result> {

        Result apply(Input input, Result lastResult);

    }
    
}

package com.test;

import java.math.BigDecimal;
import java.util.Arrays;
import java.util.List;

import com.test.util.CollectionsCustom;

public class TestCollection {

	private static  List<User> list = Arrays.asList(
			new User("张三", BigDecimal.valueOf(35.6), 18),
			new User("李四", BigDecimal.valueOf(85), 30),
			new User("赵六", BigDecimal.valueOf(66.55), 25));
	
	public static void main(String[] args) {
		//统计集合内分数之和
		testTotalScore();
		//统计集合内年龄之和
		testTotalAge();
		
	}
	
	private static void testTotalScore(){
		//统计集合内分数之和
		BigDecimal totalScore = CollectionsCustom.reduce(list, BigDecimal.ZERO, new CollectionsCustom.ReduceFunction<User, BigDecimal>() {
			@Override
			public BigDecimal apply(User input, BigDecimal lastResult) {
				// TODO Auto-generated method stub
				return lastResult.add(input.getScore());
			}
		});
		System.out.println("总共分数：" + totalScore);
	}
	
	private static void testTotalAge(){
		//统计集合内年龄之和
		Integer totalAge = CollectionsCustom.reduce(list, 0, new CollectionsCustom.ReduceFunction<User, Integer>() {
			@Override
			public Integer apply(User input, Integer lastResult) {
				// TODO Auto-generated method stub
				return lastResult += input.getAge();
			}
		});
		System.out.println("总共年龄：" + totalAge);
	}
	
	static class User{
		private String userName; //姓名
		private BigDecimal score;//分数
		private Integer age;
		public String getUserName() {
			return userName;
		}
		public void setUserName(String userName) {
			this.userName = userName;
		}
		public BigDecimal getScore() {
			return score;
		}
		public void setScore(BigDecimal score) {
			this.score = score;
		}
		public Integer getAge() {
			return age;
		}
		public void setAge(Integer age) {
			this.age = age;
		}
		public User(String userName, BigDecimal score, Integer age) {
			super();
			this.userName = userName;
			this.score = score;
			this.age = age;
		}
		public User() {
			// TODO Auto-generated constructor stub
		}
	}
	
}

总共分数：187.15
总共年龄：73