选择最佳的数据结构

Question

Name - Code (String)
A    - 123
B    - 123 
C    - 23
D    - 123
E    - 23
F    - 23
G    - 66
H    - 66

What's the best data structure to represent this data. Names should be able to iterate easily.

Edit

Names are unique. What's needed to be done is something like this. Had doubts in using Hashmap that why I asked. Code is a STRING

for( loop dataStructure names (lets say n)){ 
   if(NAME.equals(n){
     String code = dataStructure.get(n);
     do somthing 
   }
}

Answer 1

If the names are unique, a HashMap woulrd be apropriate.

You can iterate over the keys with keys() .

To iterate over the entries you can iterate over the entrySet() . See the JavaDoc of Map

If you need to perform a reverse lookup you could use the BiMap from Guava. (General a very good library)

Map entries example:

public final class MapExample {

  public static void main(String[] args) {
  Map<String, String> map = new HashMap<>();
    map.put("A", "123");

    for (Map.Entry<String, String> mapEntry : map.entrySet()) {
      if (mapEntry.getKey().equals("A")) {
        final String code = mapEntry.getValue();
        System.out.println("Your desired code: " + code);
      }
    }
  }

}

But since NAME seems to be a constant, you could simple do String code = map.get(NAME) ?

Answer 2

Sounds like a Map . Specifically, if the order of the names is important, you can use a TreeMap .

You can populate it with the put method, and then iterate over the entries (or just the keys, or just the values):

// Fill the map:
Map<String, String> map = new TreeMap<>();
map.put("A", "123");
map.put("B", "123");
// etc...

// Iterate over it:
for (Map.Entry<String, String> entry : map.entrySet()) {
    System.out.pritnln ("Key: " + entry.getKey() + " value: " + entry.getValue());
}

EDIT:
If the order is not important, as noted in later edits to the OP, a HashMap would do just fine.

Note, however, that if you're looking for a specific key, like stated in the example in the OP, there's no point in looping over the keys - you just need to use get or containsKey :

String name = ...;
String code = map.get(name);
if (code != null) {
    // do something...
}

Answer 3

I thinks you are considering this:

public enum Code {
    A("123"),
    B("123"), 
    C("23"),
    D("123"),
    E("23"),
    F("23"),
    G("66"),
    H("66");

    final public String value;

    Code(String value) {
        this.value = value;
    }
}

String h = Code.H.value;

for (Code code : Code.values()) {
    System.out.printf("Name %s, code %s%n", code, code.value);
}

Answer 4

I would suggest go for HashMap

1. The HashMap class uses a hashtable to implement the Map interface. This allows the execution time of basic operations, such as get( ) and put( ), to remain constant even for large sets

2. HashMap are efficient for locating a value based on a key and inserting and deleting values based on a key. The entries of a HashMap are not ordered.

 import java.util.HashMap; import java.util.Set; public class MyHashMapRead { public static void main(String a[]){ HashMap<String, Integer> hm = new HashMap<String, Integer>(); //add key-value pair to hashmap hm.put("A", "1"); hm.put("B", "2"); hm.put("C","3"); System.out.println(hm); Set<String> keys = hm.keySet(); for(String key: keys){ System.out.println("Value of "+key+" is: "+hm.get(key)); } } }