How to Remove Items/Entries with Specific Values from Map/HashMa

  • 时间：2020-09-07 12:13:31
  • 分类：网络文摘
  • 阅读：129 次
2091E060-120E-4C44-BAA3-7E4E0DF7BD55 How to Remove Items/Entries with Specific Values from Map/HashMap Object in Java? java programming languages

Java

In Java, you can usually remove items or entries with some specific value from Map or HashMap object using traditional method:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

public Map<String, String> removeItemByValue(Map<String, String> data, String value) {
  for (var key: data.keySet()) {
    if (data.get(key) == null) {
       data.remove(key);
    }
  }
  return data;
}
 
var data = new HashMap<String, String>();
data.put("a", "1");
data.put("b", "2");
data.put("c", "2");
removeItemByValue(data, null); 
// only prints a = 1
for (var key: data.keySet()) {
  System.out.println(key + "=" + data.get(key)); 
}
public Map<String, String> removeItemByValue(Map<String, String> data, String value) {
  for (var key: data.keySet()) {
    if (data.get(key) == null) {
       data.remove(key);
    }
  }
  return data;
}

var data = new HashMap<String, String>();
data.put("a", "1");
data.put("b", "2");
data.put("c", "2");
removeItemByValue(data, null); 
// only prints a = 1
for (var key: data.keySet()) {
  System.out.println(key + "=" + data.get(key)); 
}

A Better Map-Item Removal Approach via using values()

The values() method in Map object actually returns a Collection view of the valujes that are contained in the map object. And the remove object return null when the item is not existent anymore. Thefore, we can use the following modern 1-liner in Java to remove the items in a Map that have the specific value.

1
2
3
4

public Map<String, String> removeItemByValue(Map<String, String> data, String value) {
  while (data.values().remove(value)) ;
  return data;
}
public Map<String, String> removeItemByValue(Map<String, String> data, String value) {
  while (data.values().remove(value)) ;
  return data;
}

To double check and verify that items are actually removed:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18

package com.helloacm;
 
import java.util.HashMap;
import java.util.Map;
 
public class Main {
    public static void main(String[] args) {
        var data = new HashMap<String, String>();
        data.put("a", "b");
        data.put("e", "2");
        data.put("f", "2");
        while (data.values().remove("2"));
        // prints "a"        
        for (Map.Entry<String, String> entry: data.entrySet()) {
            System.out.println(entry.getKey());
        }
    }
}
package com.helloacm;

import java.util.HashMap;
import java.util.Map;

public class Main {
    public static void main(String[] args) {
        var data = new HashMap<String, String>();
        data.put("a", "b");
        data.put("e", "2");
        data.put("f", "2");
        while (data.values().remove("2"));
        // prints "a"        
        for (Map.Entry<String, String> entry: data.entrySet()) {
            System.out.println(entry.getKey());
        }
    }
}

–EOF (The Ultimate Computing & Technology Blog) —

推荐阅读：
香港健康卫视直播「高清」　 香港有线新闻台直播「高清」　 香港有线电视18台直播「高清」　 香港有线体育台直播「高清」　 香港有线足球台直播「高清」　 中华卫视神州台直播「高清」　 台湾卫视中文台直播-亚洲卫视中文网「高清」　 卫视体育台2在线直播「高清」　 卫视国际电影台直播_星空卫视电影台直播「高清」　 台湾三立新闻台直播「高清」　
评论列表
添加评论