java检查两个Arraylist条目是否具有相同的字段并求和

Question

我知道这个标题可能有点让人困惑，但我现在就详细介绍一下。。。 我有一个叫做Dispatch的对象，这是它的代码

public class Dispatch {
    private string DispatchName;
    private double Weight;
    ...

我的用户将选择多个调度并输入它们的权重，单击按钮后，列表将被发送到服务器，但同时，我想将同一列表保存到另一个列表，我们称之为copyList

但是在添加到copyList之前，我想检查copyList中是否已经有一个项目与我要添加的项目具有完全相同的名称（^{）。如果有，那么只需将我要添加的权重添加到列表中。如果没有同名项目，则应添加整个项目

注意：我不能使用Java 8，因为我仅限于Android API 19。我知道stream是可能的，但我需要其他解决方案

我试过使用doubleforeach，但就是找不到解决方案

Answer 1

正如评论中所建议的，试着实现Dispatch.equals如下：

@Override
public boolean equals(Object o) {
    boolean ret = false;
    if (this == o) {
        ret = true;
    } else if (o != null) && (getClass() == o.getClass()) {
        Dispatch d = (Dispatch)o;
        ret = Object.equals(DispatchName, d.DispatchName)
    }
    return ret;
}

另外，最好将代码更改为依赖Set（如HashSet<DispatchName>）并使用Set.contains()如：

DispatchName d = ...
if(hs.contains(d)) {
   DispatchName d2 = hs.get(d);
   hs.add(new DispatchName(d.DispatchName, d.Weight + d2.Weight);
} else {
   hs.add(d);
}

Answer 2

我认为实现这一点的最佳方法是建立一套数据结构，它将允许您在无需解决问题的情况下管理重复值

让我们看看列表和集合的两种方法：

带列表：

import java.util.List;

public class Dispatcher implements Comparable<Dispatcher>{

    private String DispatchName;
    private double Weight;

    public String getDispatchName() {
        return DispatchName;
    }
    public void setDispatchName(String dispatchName) {
        DispatchName = dispatchName;
    }
    public double getWeight() {
        return Weight;
    }
    public void setWeight(double weight) {
        Weight = weight;
    }

    @Override
    public int compareTo(Dispatcher o) {

        if(this.getDispatchName().equals(o.getDispatchName()))
        return 0;
        return -1;
    }

    public static void compareDispatcher(List<Dispatcher> l , Dispatcher d){

        for(Dispatcher item : l){
            if(item.compareTo(d)==0)
                item.setWeight(item.getWeight()+d.getWeight());
        }
    }

}

Note that the same logic of compareDispatcher should be used even for each insert in list to guarrantee unique logic objects .

主要示例

Dispatcher d1 = new Dispatcher();
        d1.setDispatchName("A");
        d1.setWeight(3L);

        Dispatcher d2 = new Dispatcher();
        d2.setDispatchName("B");
        d2.setWeight(1L);

        List<Dispatcher> l = new ArrayList<Dispatcher>();

        l.add(d1);
        l.add(d2);


        for(Dispatcher d : l){
            System.out.println(d.getDispatchName());
            System.out.println(d.getWeight());
            System.out.println("*************************");
        }

        System.out.println("++++++++++++++++++++++++++");

        Dispatcher d3 = new Dispatcher();
        d3.setDispatchName("A");
        d3.setWeight(2L);

        Dispatcher.compareDispatcher(l, d3);

        for(Dispatcher d : l){
            System.out.println(d.getDispatchName());
            System.out.println(d.getWeight());
            System.out.println("*************************");
        }

        System.out.println("end");

与Set:

这是最好的方法，因为实现hashcode等于保证在数据结构中看到唯一的对象

import java.util.Set;

public class Dispatcher implements Comparable<Dispatcher>{

    private String DispatchName;
    private double Weight;

    public String getDispatchName() {
        return DispatchName;
    }
    public void setDispatchName(String dispatchName) {
        DispatchName = dispatchName;
    }
    public double getWeight() {
        return Weight;
    }
    public void setWeight(double weight) {
        Weight = weight;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result
                + ((DispatchName == null) ? 0 : DispatchName.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;
        Dispatcher other = (Dispatcher) obj;
        if (DispatchName == null) {
            if (other.DispatchName != null)
                return false;
        } else if (!DispatchName.equals(other.DispatchName))
            return false;
        return true;
    }

    @Override
    public int compareTo(Dispatcher o) {

        if(this.getDispatchName().equals(o.getDispatchName()))
        return 0;
        return -1;
    }

    public static void compareDispatcher(Set<Dispatcher> l , Dispatcher d){

        for(Dispatcher item : l){
            if(item.compareTo(d)==0)
                item.setWeight(item.getWeight()+d.getWeight());
        }
    }

}

主要示例

Dispatcher d1 = new Dispatcher();
        d1.setDispatchName("A");
        d1.setWeight(3L);

        Dispatcher d2 = new Dispatcher();
        d2.setDispatchName("B");
        d2.setWeight(1L);

        Dispatcher d4 = new Dispatcher();
        d4.setDispatchName("A");
        d4.setWeight(2L);

        Set<Dispatcher> l = new HashSet<Dispatcher>();

        l.add(d1);
        l.add(d2);
        l.add(d4);

        for(Dispatcher d : l){
            System.out.println(d.getDispatchName());
            System.out.println(d.getWeight());
            System.out.println("*************************");
        }

        System.out.println("++++++++++++++++++++++++++");

        Dispatcher d3 = new Dispatcher();
        d3.setDispatchName("A");
        d3.setWeight(2L);

        Dispatcher.compareDispatcher(l, d3);

        for(Dispatcher d : l){
            System.out.println(d.getDispatchName());
            System.out.println(d.getWeight());
            System.out.println("*************************");
        }

        System.out.println("end");

Didn't add duplicate object :

Dispatcher d4 = new Dispatcher();
  d4.setDispatchName("A");
  d4.setWeight(2L);