如何将键值作为其他Map的关键？

Question

I want to put values in HashMap like below,

    map1.put("A",3);

    map1.put("A",5);
    map1.put("B",4);
    map1.put("B",8);

now I want to make ("A",3) key/value pair as key for other map like, let say ("A",3) is key1 same way for others map2.put(key1, abc);

same way for others. can you please help me to do like this???

Answer 1

You can get first hashMap entrySet and use it as key for second hashMap.

entrySet returns

Set view of the mappings contained in this map

For example,

1) Set firstMapEntries = map1.entrySet();

2) Create secondmap

3) Iterate firstMapEntries.

4)Add to second map secondMap.put(firstMapEntry, "abc")

Answer 2

You can get those (key, value) pairs as a set using the entrySet method. Iterate over that set and use the elements as keys in your other HashMap .

Something like this:

// given HashMap<String, Integer> map1:
for (Map.Entry<String, Integer> entry : map1.entrySet())
    map2.put(entry, "some string value");

Answer 3

Or you can store them in a Pair like this:

class Pair
{
    public String first;
    public Integer second;

    public Pair(String first, Integer second)
    {
        this.first = first;
        this.second = second;
    }
}

Then create a HashMap of Pair - String pairs:

HashMap<Pair, String> map = new HashMap<Pair, String>();