如何从hashmap中找到最高键值

Question

iterate with max key value so that it will replace max string value. first My code is

HashMap<String, String> mapp=new HashMap<String, String>();
mapp.put("ab","blue");
mapp.put("abc","black");
mapp.put("abcd","pink");
for (Iterator it = alltyp.iterator(); it.hasNext();) {
    String finalstring = (String) it.next();

    Iterator it1=mapp.entrySet().iterator();
    while(it1.hasNext())
    {
        Map.Entry pairs = (Map.Entry) it1.next();
        String key_ = (String) pairs.getKey();
        String value_ = (String) pairs.getValue();
        finalstring = finalstring.replaceAll(key_, value_);      
    }
}

I want to iterate with max key value means key value "abcd" should iterate first then "abc" then "ab".

Answer 1

Here is an example using Collections.max(). You can also pass a comparator if you want a custom ordering.

HashMap<String, String> mapp=new HashMap<String, String>();
mapp.put("ab","blue");
mapp.put("abc","black");
mapp.put("abcd","pink");

// find max key alphabetically
String maxKey = Collections.max(mapp.keySet());


Comparator<String> strLenCmp = new Comparator<String>() {
    @Override
    public int compare(String o1, String o2) {
        return Integer.compare(o1.length(), o2.length());
    }
};

// find max key by key length
String longKey = Collections.max(mapp.keySet(), strLenCmp);

Edit : added example with custom Comparator

Answer 2

Use Generics, get rid of the casting. That will tidy up your code a lot.

You will need a custom comparator to do the sorting.

Once you have the comparator you have two choices:

Option 1:

Create an ArrayList, dump all the keys from the map into it.

Sort the ArrayList, iterate over the sorted ArrayList.

Option 2:

Use a TreeMap to store the data.

Answer 3

Try using the TreeMap instead of HashMap it has the method for getting the last entry which will give you the entry which has the highest value of key. Even in TreeMap if you pass your custom Comparator then it will be sorted in a way that you will get the key with max value first so you don't have to worry about it.

TreeMap - lastEntry

Refer this link, and lastEntry method.