在对象的arraylist的特定属性中搜索

Question

我有一个对象的arraylistarraylist List Tile有新瓷砖的属性（“color”,value)我想创建一个搜索函数，在这里我迭代遍历瓷砖的每个colour属性和arraylist中每个颜色内的每个value属性（就像每个循环的嵌套），有没有一种简单的方法可以做到这一点？

Answer 1

假设tile类有两个属性stringcolour和intvalue。它有一个ToString(java.lang.Object Class的重写方法），如下所示：

@Override public String toString() {
    return colour + ":" + value;
}

制作一些瓷砖：

Tile t1 = new Tile("red", 7); // constructor takes a colour and a value
Tile t2 = new Tile("red", 2);
Tile t3 = new Tile("blue", 9);
Tile t4 = new Tile("white", 17);
Tile t5 = new Tile("blue", 3);
Tile t6 = new Tile("red", 15);
Tile t7 = new Tile("white", 10);

方案1：

private static List<Tile> getTilesWithColor1(List<Tile> tilesList, String searchColor) {
    return tilesList.stream()
                     .filter(tile -> tile.getColour().equals(searchColor))
                     .collect(Collectors.toList());
}

private static List<Tile> getTilesWithColor2(List<Tile> tilesList, String searchColor) {
    List<Tile> result = new ArrayList<>();
    for (Tile t : tilesList) {
        if (t.getColour().equals(searchColor)) {
            result.add(t);
        }
    }
    return result;
}

null

我想做一个搜索函数，在这里我迭代遍历Tile的每个颜色属性和arraylist中的每个颜色中的每个值属性（就像嵌套的for each循环），有没有一个简单的方法可以做到这一点呢？

您可以更改此函数以添加附加条件或过滤器以获得所需的结果。

方案2：

private static Map<String, List<Integer>> getTileColorsAndValues(List<Tile> tilesList) {
    return tilesList.stream()
                     .collect(Collectors.groupingBy(Tile::getColour,
                         Collectors.mapping(Tile::getValue, Collectors.toList())));
}

null

List<Integer> valuesList = map.get("red");

方案3：

按颜色获取所有瓷砖：

private static Map<String, List<Tile>> getTilesByColorsAndValues(List<Tile> tilesList) {
    return tilesList.stream()
                    .collect(Collectors.groupingBy(Tile::getColour));
}

• 输入:TilesList
• 输出:{red=[red:7,red:2,red:15],white=[white:17,white:10],blue=[blue:9,blue:3]}

List<Tile> tilesList = map.get("red");

示例的代码：

import java.util.*;
import java.util.stream.*;
import java.util.function.*;

public class TilesExample {

    public static void main(String [] args) {

        Tile t1 = new Tile("red", 7);
        Tile t2 = new Tile("red", 2);
        Tile t3 = new Tile("blue", 9);
        Tile t4 = new Tile("white", 17);
        Tile t5 = new Tile("blue", 3);
        Tile t6 = new Tile("red", 15);
        Tile t7 = new Tile("white", 10);
        List<Tile> tilesList = Arrays.asList(t1, t2, t3, t4, t5, t6, t7);

        System.out.println(getTilesWithColor1(tilesList, "red"));
        System.out.println(getTilesWithColor2(tilesList, "red"));

        System.out.println(getTileColorsAndValues(tilesList));

        System.out.println(getTilesByColorsAndValues(tilesList));
    }

    private static Map<String, List<Tile>> getTilesByColorsAndValues(List<Tile> tilesList) {
        return tilesList.stream()
                        .collect(Collectors.groupingBy(Tile::getColour));
    }

    private static Map<String, List<Integer>> getTileColorsAndValues(List<Tile> tilesList) {
        return tilesList.stream()
                        .collect(Collectors.groupingBy(Tile::getColour,
                            Collectors.mapping(Tile::getValue, Collectors.toList())));
    }

    private static List<Tile> getTilesWithColor1(List<Tile> tilesList, String searchColor) {
        return tilesList.stream()
                         .filter(tile -> tile.getColour().equals(searchColor))
                         .collect(Collectors.toList());
    }

    private static List<Tile> getTilesWithColor2(List<Tile> tilesList, String searchColor) {
        List<Tile> result = new ArrayList<>();
        for (Tile t : tilesList) {
            if (t.getColour().equals(searchColor)) {
                result.add(t);
            }
        }
        return result;
    }
}