I have hashmap Key is String composed of concatenation of 3 elements (element1+element2+element3)
String key=element1+element2+element3;
which is put in the hashmap
HashMap<String,Object> map=new Hashmap<String,Object>();
map.put(key,new Object());
i want to remove all the entries in the hashmap matching key having element2 if(key.contains("element2")) then remove that entry in hashmap.
How accomplish this?
Hash map needs an exact key - accessing by a partial key is not possible, meaning that you would need to iterate all keys, check for match on "element2", and remove elements as you go:
Iterator<Map.Entry<String,Object>> iter = map.entrySet().iterator();
while(iter.hasNext()){
Map.Entry<String,Object> entry = iter.next();
if (entry.key().contains("element2")) {
iter.remove();
}
}
we could also use Pattern and Matcher functionality
public class TestMatcher {
public static void main(String[] args) {
Map<String, Integer> sampleData = new HashMap<String, Integer>();
sampleData.put("data1data21data3", new Integer(1));
sampleData.put("data1data2A", new Integer(1));
sampleData.put("data1data3", new Integer(1));
sampleData.put("data3", new Integer(1));
TestMatcher tm = new TestMatcher();
tm.printMatchKey("data2[A-Z0-9]{1}", sampleData);
}
public void printMatchKey(String regex, Map<String, Integer> data) {
Pattern pattern = Pattern.compile(regex);
Iterator<String> keyIterator = data.keySet().iterator();
while(keyIterator.hasNext()) {
String key = keyIterator.next();
Matcher matcher = pattern.matcher(key);
if (matcher.find()) {
System.out.println("Key " + key + " contains " + regex);
}
}
}
}
Related to this.
Simple way is to get keySet() from your map which
Returns a Set view of the keys contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa.
So
yourMap.keySet().removeIf(key -> key.contains(keyPart));
Have a look at this.. A regex map which has regular expressions as its key so you wont need to iterate through all key value pairs yourself .. its a custom map implementation..
