Find if HashMap contains chosen value and return key

Question

Is there any way to find if my HashMap<String, String> contains entry ( key,value) with value="x" and to go through all entries sequentially ?

Answer 1

HashMap.containsKey()

This is what HashMap is made for in the first place...

(Not sure what you mean by "to go through all entries sequentially", though. There's only 1 entry per key.)

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Edit:

Now that you edited the question, the answer is no! :(

If you need that feature, design your own two-way HashMap that stores the location of each value in the other's value (hopefully that made sense), and then use that class. HashMaps aren't designed for this.

Answer 2

There is the containsValue() method, but for common implementations this just internally iterates through all values and compares them to the parameter.

Answer 3

A common pattern is to use

if(hashMap.containsKey(key)) {
    Object o = hashMap.get(key);

}

however if you know none of the values are null (Many Map collections do not allow null) then you can do the following which is more efficient.

Object o = hashMap.get(key);
if (o != null) {

}

BTW: containsKey is the same as

Set<Key> keys = hashMap.keySet();
boolean containsKey = keys.contains(key);