如何对list对象中指定值进行汇总呢?

list指定汇总的实现思路

借助
 Collectors.summingLong
即可实现list对象汇总操作

package com.java265.other;

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class Test21 {



	/**
	 * java265.com list单个属性求和
	 */
	public static void main(String[] args) {

		List list = new ArrayList<>();
		list.add(new Test21(1, "java1"));
		list.add(new Test21(22, "java265"));
		list.add(new Test21(8, "java我最爱的语言"));
		list.add(new Test21(99, "java最牛"));

		list.stream().forEach(System.out::println);

		// 求qty的合计
		Long total = list.stream().collect(Collectors.summingLong(Test21::getQty));
		System.out.println("total:" + total);
	}

	private Integer qty;
	private String name;

	public Integer getQty() {
		return qty;
	}

	public void setQty(Integer qty) {
		this.qty = qty;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public Test21() {
	}

	public Test21(Integer qty, String name) {
		this.qty = qty;
		this.name = name;
	}

	@Override
	public String toString() {
		return "Test21 [qty=" + qty + ", name=" + name + "]";
	}

}