Map (Hashmap) to Array
Hello Java Friends,
Please, I have a map(Mappings = new HashMap<String, Integer>) which contains both String and Integer elements. I wanted to store the string elements of the Map in a String Array and Integer elements in Integer Array but end up with error messages. How can I implement it?
See part of my code below:
publicclass Tryit{
private Map<String, Integer> Mappings;
String[]StringElem;
int [] IntegerElem;
public Tryit(){
Mappings =new HashMap<String, Integer>()
StringElem =new String [100];
IntegerElem =newint [100];
-
-
-
for (String index : Mappings.KeySet()){
StringElem = index;
}
for (int i : Mappings.values(){
IntegerElem = i;
}
}
}
[1430 byte] By [
Jona_Ta] at [2007-11-27 0:35:50]
> String[] StringElem;
> int [] IntegerElem;
> ...
> for (String index : Mappings.KeySet()){
> StringElem = index;
> }
> for (int i : Mappings.values(){
> IntegerElem = i;
> }
StringElem is an array of String. index is a String.
You cannot assign a String to an array of String. (incompatible type)
Likewise, you cannot assign i to integerElem (incompatible type).
Hope that reminds you of how you should fix it now.
A Map can give you its keySet() (which is a Set) and its values() whichis a Collection; both a Set and a Collection can be transmogrified toan array, using the *ahem* toArray() method.The Arrays utility class knows how to sort arrays.kind regards,Jos
JosAHa at 2007-7-11 22:44:45 >
import java.util.*;
public class ToArrayExample {
public static void main(String[] args) {
//create example map
Map < String, Integer > m = new HashMap < String, Integer > ();
m.put("one", 1);
m.put("two", 2);
m.put("three", 3);
m.put("four", 4);
//copy to arrays
int size = m.size();
String[] keys = new String[size];
Integer[] vals = new Integer[size];
m.keySet().toArray(keys);
m.values().toArray(vals);
//display
System.out.format("keys = %s%n", Arrays.toString(keys));
System.out.format("vals = %s%n", Arrays.toString(vals));
}
}
In addition to JosAH's and DrLaszloJamf's advice, you might
also want to look at the entrySet() method,
which is more efficient than calling keySet() and values().
Just have a loop like this:
String[] names = new String[map.size()];
int[] numbers = new int[map.size()];
int i=0;
for(Map.Entry<String,Integer> e: map.entrySet()) {
names[i] = e.getKey();
numbers[i] = e.getValue();
i++;
}
Hello KathyMcdonnel, JosAH and DrLaszloJamf,I thank you all for the help.Jona_T
Hello friends,
The idea you gave me worked but still I am having a small problem: I have two classes, class A and B. In Class A, I implemented a set and get method which I will use in Class B to retrieve the keys and Values. But when I call the get method in Class B, I always get null. The arrays in both classes are all declared globally.
Get and Set Method in Class A :
public void setKeyValues() {
int i = 0;
for(Map.Entry<String, Integer> e: map.entrySet()) {
ElementName[i]= e.getKey();
i++;
}
}
public String []getKeyValues(){
return ElementName;
}
Call the Get Method in Class B
import package X.A
public class B{
private String [] names;
public B(){
A bix = new A();
int length = bix.getKeyValues().length;
names = new String[length];
-
System.out.printf ("%d", gettingKeys(bix.getKeyValues());
-
-
}
public String[] gettingKeys(String []naming) {
names = new int[bix.getKeyValues().length];
int size = naming.length;
for (int p = 0; p < size; p++) {
names[p]=naming[p];
p++;
}
return names;
}
}
Please where is the problem ? I am unable to read and print the map values and keys from another friend class.
Jona_T
