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Java Collection Q&A
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14.Garbage Collection
Java Collection Q&A » Map » Integer 

1. Mapping of strings to integers

What is the easiest way in Java to map strings (Java String) to (positive) integers (Java int), so that

  • equal strings map to equal integers, and
  • different strings map to different integers?
So, similar ...

2. What is the best map implementation to use when storing integers with char keys?

I have a set of flags which are part of a huge text data file as single characters. Before processing the file I map each flag to the id of a property ...

3. Readable way of knowing if there is at least one difference between two Map in Java?

I have two maps of type Map<Long, Integer>, one named "old" representing the old state of an object, and the other named "new" representing the new state of the same object. Is ...

4. Map equality using Hamcrest

I'd like to use hamcrest to assert that two maps are equal, i.e. they have the same set of keys pointing to the same values. My current best guess is:

assertThat( affA.entrySet(), hasItems( ...

5. Set inside Map

I have a question. First, I declared a map:

Map<TwoIntClass, Set<Integer>> m = new HashMap<TwoIntClass, Set<Integer>>();
Now, I want to put stuff inside this map, something like
int num = 7;
m.put(new TwoIntClass(5, 3), ?? ...

6. Mapping specific strings to constant integers?

Given a specific set of strings, what's the best way to map them to a corresponding set of integers? Say I have a class with a few integer constants that I ...

7. Sorting an int array, tied to a string array in Java

I have two arrays:

int[] intArray = new int[]{point1,point2,point3,point4};

String[] strArray = new String[]{worda,wordb,wordc,wordd};
Now, I want to sort intArray in numerical order, such that strArray follows the same order. I'm sure this is ...

8. Map sequence of integers into repeating sequence

I have a continuous, ordered sequence of integers that start less than zero and go above zero; for instance ...,-5,-4,-3,-2,-1,0,1,2,3,4,5,6,7. I need to map these into a repeating sequence 3,6,9,12, with ...

9. How to randomly select a key based on its Integer value in a Map with respect to the other values in O(n) time?

If we have a Map<T, Integer>, let's say the Integer value represents "how many" Ts there are. Thus, I want to uniformly select a T based on its Integer value. If ...

10. Mapping a String to an array of ints - Java

How do I map a String to a statically defined array of ints? I tried

private static Map<String, int[]> map = new HashMap<String, int[]>();
static {
    map.put("foo", {5, 1, 3, ...

11. TreeMap returns an single value in java

TreeMap<Integer, String> map = new TreeMap<Integer, String>();

    map.put(1, "example");
    map.put(1, "example2");
    map.put(1, "example3");

    Iterator<Integer> itr = map.keySet().iterator();


12. Inserting Integers into a TreeMap

I want to store the IDs of items and their corresponding co-ordinates. For this, I'm using a TreeMap where Coordinates is a class containing int x and int y. Now, for ...

13. How to represent a small map of integers as an array?

Let's say I want to build a small simple map, where the key is N integers (fixed, usually one) and the value is M integers (also fixed, usually one). Now I would ...

14. In a Java Map , do I need to put the Double[] after getting and modifying?

A quick question which maybe is lame. In the following code:

Map<Integer, Double[]> dataMap = new Map<Integer, Double[]>();
dataMap.put(1, new Double[]{100,100});
Double[] dob = dataMap.get(1);
dob[0] = 100;
dob[1] = 200;
dataMap.put(1, dob);
Is the last "dataMap.put" instruction necessary? ...

15. There is a Collection which can I hold a String and an Integer with repetead values?

I have an text and I will do some filtering based in the number of the words of each phrase. I was thinking in using a Map, in the key I put ...

16. Integer incompatible Joda and Java lang

Getting this error:

 incompatible types
    required: java.lang.Integer
    found: java.util.Map.Entry<>
and the code resulting in error:
public static void checkRange() {


17. Treemap: Problem doing put(int, double)

18. Big Collection, integer key

is the collection going to grow at some point? will it eventually become a million or a billion or more elements? How often are elements added or deleted? Also, how often do you need to do this? if you are going to search for an element millions of times, you may do better to take the performance hit and sort it ...

19. Map or Map

Personally i feel it would increase performance (a little) Strings have an overhead of using the string pool. So when you create a key, a lot ot stuff happens. Integers on the other hand are easier to create and destroy. Furthermore, Strings are backed by an array of characters. So a key like 11221 will be 10 byte while the same ...

20. Mapmylist

22. TreeMap reverse sort Integers

23. map.remove(new Integer(id)); memory leak?

First, your synchronization seems a bit lacking (unsynchronized adding/removing as far as I can see). Consider using Collections.synchronizedMap to wrap your HashMap, then you can skip all homemade synchronization as it's taken care of for you. Second, if you can, it would be a good idea to increase the memory your program has access to. The default is 64Mb, but if ...  | Contact Us | Privacy Policy
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