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Increment Key in a collection

I have a collection say
Map<Integer,Integer> myMap=new Map<Integer,Integer>();
myMap.put(1,"a");
myMap.put(2,"b");
myMap.put(3,"c");
My map currently has {1="a",2="b",3="c"}.
Suppose I want to put a value say myMap.put(1,"d")
So is there a way that I am able to add the existing key and incrementing the remaining key so my output map be like
{1="d",2="a",3="b",4="c"} ?

You will have to iterate over all the elements of the Map in order to modify the values for all the existing keys.
For example, woth Java 8 Streams you can produce a new Map where the keys are incremented, and then add the new Entry :
map = map.entrySet().stream().collect(Collectors.toMap(e->e.getKey()+1,e->e.getValue()));
map.put(1,"d");
However, if your keys are consecutive integers (as your example suggests), why not use an ArrayList<String> instead of a Map<Integer,String>? This will give you the functionality you want by simply calling list.add(0,"d"); (with the small difference of the indices starting at 0 instead of 1).

Iterating over a key set of a LinkedHashMap

is it possible to retrieve the next (next, as in the next key value which has been inserted) key value of a LinkedHashMap?
E.g. the current key value is 2 and the next key value is 4. I want to use the value of the next key without setting my iterator (or whatsoever) one index further. Apparently using one iterator doesn't seem to do the job. Another idea would be to cast the set returned by myHashMap.keySet() to some other implementing class but I am not sure if it is possible to retrieve the next element.
Any ideas?

Assume there is LinkedHashMap<K,V> linkHashMap, now define a custom method getNextKey which takes a parameter index and return the next index value if valid.
Code snippet (not working code)-
public K getNextKey(int index){
// put check if index is valid
K[] keyArray = linkedHasMap.keySet.toArray(new K[linkedHasMap.size()]);
return K[index+1];
}

How to find intersection of two keys in Redis using Java?

I have two keys in the Redis. First key contains set of strings as a value.Second key contains the sorted set of object(String as a value and score ). I want to fetch elements where string in first key and string field of the object in the second key are similar.
If I replace object with a string in the second key,I am able to fetch but I want to fetch list of strings along with their score.
I am using Spring-data-redis and jedis for Redis handling.
Is it possible to fetch list of common strings and their corresponding score? If yes, how.

How you are storing your data will affect how you want to retrieve it. By storing your keys as listed in the comment, you are basically limited to string manipulation to determine anything useful, and that really isn't the value of using Redis. (It's not meant for "searching", its meant for fast lookups.)
Consider something like this:
The keys used in Redis will be your first set of strings, each containing a list of values. The values in those lists will be your second set of strings, and may be duplicated in different lists (as you see fit).
LPUSH "x1" "POJO[field1=x1, field2=y1]" "POJO[field1=x1, field2=y2]"
LPUSH "x2" "POJO[field1=x2, field2=y2]"
etc...
When you want the values of your first number
LRANGE x1 0 1000 (or LLEN x1 --> "result", then LRANGE x1 0 "result")

How can I use a map for calculations?

I'm working on a program for class. Using a TreeMap to store IDs (String - Key) and earnings amounts (double - value). I'm importing the values from a text file using a Scanner. My problem at the moment is that I need the values to accumulate rather than overwriting with the last value read. So my question is how do you use a Map to do calculations like that? Any help would be appreciated.

There is no implicit functionality in Map. Idea behind your homework assignment is for you to learn how to insert, find, get and replace to/from a Map. There are functions for each of these and ou should use all to get this done.

When adding a new value to your map, if the key already exists, you can get the associated value, add the new value to it, and put it back into the map. Example:
// Assuming that key and value were read from your file, and that
// myMap is declared as "Map<String, Double>"
if (myMap.containsKey (key)) {
double oldValue = myMap.get (key);
value += oldValue;
}
myMap.put (key, value);

1) Check whether value with same key exists in the map
2) If it exists then read it and add the currently read value. Put it back into map

problem getting value from HashMap

Hi all I'm using a HashMap to hold one of my object with a string key. when I put an object with a key it has no problem, when I put my second object I got my object added but can't get it with its key. Somewhat it goes to somewhere that is "next". I took a screenshot from debug mode (eclipse), below
although size shows 2, I can't see my second item in hashmap, but in other hashmap's next node.
To note something I use my key like in a form "name.tag", tag and name in same time can never be the same, but "tag" can be the same. does hashmap has something to do with dot operator when evaluating keys? I hope I could write clearly,
Thanks in advance
Edit:
Here is a piece of code I use to create my hashmap
private HashMap<String,ParameterItem> parseParametersNode(DataModel parent,Element element){
NodeList parameterChilds=element.getChildNodes();//gep element parameters
HashMap<String, ParameterItem> parameterItems=new HashMap<String, ParameterItem>();
for(int i=0;i<parameterChilds.getLength();i++){
if(parameterChilds.item(i).getNodeType()==Node.ELEMENT_NODE){
Element el=(Element) parameterChilds.item(i);
NamedNodeMap atts=el.getAttributes();
ParameterItem item=new ParameterItem();
for(int j=0;j<atts.getLength();j++){
Attr attribute=(Attr) atts.item(j);
String attributeValue=attribute.getValue();
String attributeName=attribute.getName();
item.setParsedProperty(attributeName, attributeValue);
} /*check attributes later*/
//finish loop and insert paramitem to params
String key="key"+i;
if(item.getTag()!=null && item.getName()!=null)
key=item.getName()+"."+item.getTag();
parameterItems.put(key, item);
// testParam=item;
// parameterItems.put(key, testParam);
}
}
return parameterItems;
}

There is not really a problem here: you have a hash collision. That is, both of your keys have been placed in the same hash bucket. It appears you have only four buckets (odd, I thought the initial default was 10 or 16), so the chance of that with random data is 25 percent. Your size incremented just fine. The next is the internal implementation’s way of pointing to the next element in the same bucket. If the number of elements in each buckets gets too big, Java will internally rehash into more buckets.
I do not see why you need a HashTable here since you are numbering your keys consecutively (you could use an ArrayList), but maybe this is just starter code and your real use case is different.

You have the code:
String key="key"+i;
but right after this you set key again not adding to it:
if(item.getTag()!=null && item.getName()!=null)
key=item.getName()+"."+item.getTag();
Should this be key +=item.getName()+"."+item.getTag(); ?