List集合中根据相同属性的对象合并计算

最新推荐文章于 2023-04-10 18:44:22 发布

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本文介绍了一种在Java中使用List集合，通过重写equals和hashCode方法，并定义merge方法，来实现根据对象的特定属性进行合并及计算总和的技巧。具体展示了如何将具有相同name和date属性的S类对象进行合并，同时累加其value属性。

List集合中根据相同属性的对象合并计算

package com.thinkgem.jeesite.modules.test.web;

public class S {

    private String name;
    private String date;
    private int value;


    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((date == null) ? 0 : date.hashCode ());
        result = prime * result + ((name == null) ? 0 : name.hashCode ());
        return result;
    }


    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass () != obj.getClass ())
            return false;

        S other = (S) obj;
        if (date == null) {
            if (other.date != null)
                return false;
        } else if (!date.equals ( other.date ))
            return false;

        if (name == null) {
            if (other.name != null)
                return false;
        } else if (!name.equals ( other.name ))
            return false;
        return true;
    }

    static S merge(S s1, S s2) {
        if (!s1.equals ( s2 )) {
            throw new IllegalArgumentException ();
        }
        return new S ( s1.name, s1.date, s1.value + s2.value );
    }

    @Override
    public String toString() {
        return "S{" +
                "name='" + name + '\'' +
                ", date='" + date + '\'' +
                ", value=" + value +
                '}';
    }

    public S(String name) {
        this.name = name;
    }

    public S(String name, String date, int value) {
        this.name = name;
        this.date = date;
        this.value = value;
    }

    public String getName() {
        return name;
    }

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

    public String getDate() {
        return date;
    }

    public void setDate(String date) {
        this.date = date;
    }

    public int getValue() {
        return value;
    }

    public void setValue(int value) {
        this.value = value;
    }
}

上面是实体，需要重写equals入hashcode方法，定义merge方法

下面是测试类

package com.thinkgem.jeesite.modules.test.web;

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


public class Test {

    public static void main(String[] args) {
        List<S> list = new ArrayList<S> ();
        list.add(new S("小刘" ,   "2015/9/1",   2));
        list.add(new S("小刘" ,   "2015/9/2",   3));
        list.add(new S("小强" ,   "2015/9/1",   4));
        list.add(new S("小强" ,   "2015/9/1",   5));
        list.add(new S("小刘" ,   "2015/9/1",   6));
        list.add(new S("小图" ,   "2015/9/1",   7));
        list.add(new S("小刘" ,   "2015/9/1",   8));
        list.add(new S("小图" ,   "2015/9/1",   9));
        list.add(new S("小刘" ,   "2015/9/2",   99));
        Map<S, S> map = new HashMap<S, S> ();
        for (S s : list) {
            if (map.containsKey(s)) {
                map.put(s, S.merge(s, map.get(s)));
            } else {
                map.put(s, s);
            }
        }
        System.out.println(map.values());
    }

}

打印结果如下

[S{name='小图', date='2015/9/1', value=16},

S{name='小刘', date='2015/9/1', value=16},

S{name='小强', date='2015/9/1', value=9},

S{name='小刘', date='2015/9/2', value=102}]

然后就可以了