如果键已经存在于HashMap中，则添加新值

Question

我有一个带有某些条目的ArrayList >>。 每个条目都有一个“ ID”，它可以类似于其他条目。

我想检查两个（或多个）条目是否具有相同的ID，然后为它们分配颜色。 如果不是，则分配下一个颜色并在地图上添加分配的颜色值。

这是我的代码：

String[] colorPallete =new String[] {"#1F1A17", "#62934D", "#F9B03F", "#7959BC", "#74B8DE", "#E65641", "#7CC8BB", "#D7CE5D", "#D6BE95", "#B694D1"};



 map = new HashMap<String,String>();
 map.put(NEWSSOURCETITLE, title);
 map.put(DESCRIPTION, description);
 map.put(ID, newsId);
 myNewsList.add(map);

我该如何实现？

Answer 1

使用map ，它将ID映射到颜色。 然后遍历您的ArrayList并执行以下操作：

• 如果地图已经包含ID，则从中获取颜色并分配给您的条目。
• 如果地图不包含ID，则获取新颜色，将其分配给您的条目，然后将ID-color条目放入地图中。

伪代码可以做到这一点：

Map<String, String> idToColor = new HashMap<>();

for (...) {
  if (idToColor.contains(entry.id)) {
    entry.color = idToColor.get(id);
  } else {
    entry.color = generateNewColor();
    idToColor.put(entry.id, entry.color);
  }
}

Answer 2

也许这个测试代码会有用：

public class Test11 {
    static String[] colorPallete = new String[] {"#1F1A17", "#62934D", "#F9B03F", "#7959BC", "#74B8DE", "#E65641", "#7CC8BB", "#D7CE5D", "#D6BE95", "#B694D1"};

    public static void main(String[] args) {
        Map<String, String> idToColorMap = new HashMap<String, String>();

        List<News> newsList = new ArrayList<News>();
        newsList.add(new News("1", "title1", "description1"));
        newsList.add(new News("2", "title2", "description2"));
        newsList.add(new News("1", "title3", "description3"));
        newsList.add(new News("5", "title4", "description4"));
        newsList.add(new News("2", "title5", "description5"));
        newsList.add(new News("1", "title6", "description6"));
        newsList.add(new News("1", "title7", "description7"));
        newsList.add(new News("3", "title8", "description8"));
        newsList.add(new News("4", "title9", "description9"));
        newsList.add(new News("5", "title10", "description10"));
        newsList.add(new News("1", "title11", "description11"));
        newsList.add(new News("6", "title12", "description12"));

        int colorIndex = 0;
        for (int i = 0; i < newsList.size(); i++) {
            if (newsList.size() > 1 && !idToColorMap.containsKey(newsList.get(i).getId())) {
                News currentNews = newsList.get(i);
                currentNews.setColor(colorPallete[colorIndex]);
                idToColorMap.put(currentNews.getId(), colorPallete[colorIndex]);

                for (int j = i + 1; j < newsList.size(); j++) {
                    if (newsList.get(j).getId().equals(currentNews.getId())) {
                        newsList.get(j).setColor(colorPallete[colorIndex]);
                    }
                }

                if (++colorIndex == colorPallete.length) {
                    colorIndex = 0;
                }
            } else {
                newsList.get(0).setColor(colorPallete[0]);
                idToColorMap.put(newsList.get(0).getId(), colorPallete[0]);
            }
        }

        for (News news: newsList) {
            System.out.println("News id=" + news.getId() + ", title=" + news.getTitle() + ", description=" + news.getDescription() + ", color=" + news.getColor());
        }

        for (Map.Entry<String, String> entry: idToColorMap.entrySet()) {
            System.out.println("Id to color: id=" + entry.getKey() + ", color=" + entry.getValue());
        }
    }
}

class News {
    String id;
    String title;
    String description;
    String color;

    News(String id, String title, String description) {
        this.id = id;
        this.title = title;
        this.description = description;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }
}

打印：

• 新闻ID = 1，标题=标题1，描述=描述1，颜色=＃1F1A17
• 新闻ID = 2，标题= title2，描述= description2，颜色=＃62934D
• 新闻ID = 1，标题= title3，描述= description3，颜色=＃1F1A17
• 新闻ID = 5，标题= title4，描述= description4，颜色=＃F9B03F
• 新闻ID = 2，标题= title5，描述= description5，颜色=＃62934D
• 新闻ID = 1，标题= title6，描述= description6，颜色=＃1F1A17
• 新闻ID = 1，标题= title7，描述= description7，颜色=＃1F1A17
• 新闻ID = 3，标题= title8，描述= description8，颜色=＃7959BC
• 新闻ID = 4，标题= title9，描述= description9，颜色=＃74B8DE
• 新闻ID = 5，标题= title10，描述= description10，颜色=＃F9B03F
• 新闻ID = 1，标题= title11，描述= description11，颜色=＃1F1A17
• 新闻ID = 6，标题= title12，描述= description12，颜色=＃E65641
• 标识颜色：id = 3，颜色=＃7959BC
• 颜色ID：ID = 2，颜色=＃62934D
• 标识颜色：id = 1，颜色=＃1F1A17
• 颜色ID：ID = 6，颜色=＃E65641
• 颜色ID：ID = 5，颜色=＃F9B03F
• 颜色ID：ID = 4，颜色=＃74B8DE

Answer 3

首先创建一个对象类来存储新闻数据。 即

public class NewsData {
      String newsSourceTitle;
      String description;
      String id;   
      public NewsData(String title, String desc, String id) {
          this.newsSourceTitle = title;
          this.description = desc;
          this.id = id;
      }      
   // write getter for fields
  }

根据您的要求，请使用以下代码段：

class NewsColour {
        String[] colorPallete = new String[] {"#1F1A17", "#62934D", "#F9B03F", "#7959BC", "#74B8DE", "#E65641", "#7CC8BB", "#D7CE5D", "#D6BE95", "#B694D1"};

        int colorIndex = 0;

        private String getNextColor() {
         return (colorIndex < colorPallete.length) ? colorPallete[colorIndex++] :      colorPallete[colorIndex++%colorPallete.length];
        }

     // Change with your method
     public void setNewsColor() {
        NewsData newsData1 = new NewsData("title1", "desc1", "xxxx");
        NewsData newsData2 = new NewsData("title2", "desc2", "xxxx");
        NewsData newsData3 = new NewsData("title3", "desc3", "xxxx2");
        NewsData newsData4 = new NewsData("title4", "desc4", "xxxx3");
        NewsData newsData5 = new NewsData("title5", "desc5", "xxxx2");

        List<NewsData> myNewsList = new ArrayList<NewsData>();

        myNewsList.add(newsData1);
        myNewsList.add(newsData2);
        myNewsList.add(newsData3);
        myNewsList.add(newsData4);
        myNewsList.add(newsData5);

        Map<String, String> newsNColorMap = new HashMap<String, String>();

        for (NewsData news : myNewsList) {
            String newsColor = newsNColorMap.get(news.getId());
            if (null == newsColor) {
                newsColor = getNextColor();
                newsNColorMap.put(news.getId(), newsColor);            
            }
            // Putting Syso just for printing color. Change this as per your requirement.
            System.out.println("News title/id: " + news.getTitle() + "/" + news.getId() + " Color: " + newsColor); 
    }
     }

上面代码的输出是 ：

新闻标题/编号：title1 / xxxx颜色：＃1F1A17

新闻标题/编号：title2 / xxxx颜色：＃1F1A17

新闻标题/ id：title3 / xxxx2颜色：＃62934D

新闻标题/ id：title4 / xxxx3颜色：＃F9B03F

新闻标题/ id：title5 / xxxx2颜色：＃62934D

Answer 4

要知道ArrayList是否包含元素，请使用contains 。

List<String> list = new ArrayList<String>();
list.add(...);

if (list.contains("a value")) {
   //do something
}

要知道Map是否containsKey元素，请使用containsKey或containsValue 。

Map<String, String> map = new HashMap<String, String>();
map.put(...);

if (map.containsKey("a key")) {
   //do something
}