Java - The Map.Entry Interface
The Map.Entry interface enables you to work with a map entry.
The entrySet( ) method declared by the Map interface returns a Set containing the map entries. Each of these set elements is a Map.Entry object.
Following table summarizes the methods declared by this interface −
| Sr.No. |
Method & Description |
| 1 |
boolean equals(Object obj)
Returns true if obj is a Map.Entry whose key and value are equal to that of the invoking object.
|
| 2 |
Object getKey( )
Returns the key for this map entry.
|
| 3 |
Object getValue( )
Returns the value for this map entry.
|
| 4 |
int hashCode( )
Returns the hash code for this map entry.
|
| 5 |
Object setValue(Object v)
Sets the value for this map entry to v. A ClassCastException is thrown if v is not the correct type for the map. A NullPointerException is thrown if v is null and the map does not permit null keys. An UnsupportedOperationException is thrown if the map cannot be changed.
|
Example 1
Following is an example showing how Map.Entry can be used to get values of a map entry −
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
public class HashMapDemo {
public static void main(String args[]) {
// Create a hash map
HashMap<String, Double> hm = new HashMap<>();
// Put elements to the map
hm.put("Zara", Double.valueOf(3434.34));
hm.put("Mahnaz", Double.valueOf(123.22));
hm.put("Ayan", Double.valueOf(1378.00));
hm.put("Daisy", Double.valueOf(99.22));
hm.put("Qadir", Double.valueOf(-19.08));
// Get a set of the entries
Set<Map.Entry<String, Double>> set = hm.entrySet();
// Get an iterator
Iterator<Map.Entry<String, Double>> i = set.iterator();
// Display elements
while(i.hasNext()) {
Map.Entry<String, Double> me = i.next();
System.out.print(me.getKey() + ": ");
System.out.println(me.getValue());
}
}
}
Output
Daisy: 99.22
Ayan: 1378.0
Zara: 3434.34
Qadir: -19.08
Mahnaz: 123.22
Example 2
Following is an example showing how Map.Entry can be used to set values of a map entry −
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
public class HashMapDemo {
public static void main(String args[]) {
// Create a hash map
HashMap<String, Double> hm = new HashMap<>();
// Put elements to the map
hm.put("Zara", Double.valueOf(3434.34));
hm.put("Mahnaz", Double.valueOf(123.22));
hm.put("Ayan", Double.valueOf(1378.00));
hm.put("Daisy", Double.valueOf(99.22));
hm.put("Qadir", Double.valueOf(-19.08));
// Get a set of the entries
Set<Map.Entry<String, Double>> set = hm.entrySet();
// Get an iterator
Iterator<Map.Entry<String, Double>> i = set.iterator();
// Display elements
while(i.hasNext()) {
Map.Entry<String, Double> me = i.next();
me.setValue(me.getValue() * 10);
System.out.print(me.getKey() + ": ");
System.out.println(me.getValue());
}
}
}
Output
Daisy: 992.2
Ayan: 13780.0
Zara: 34343.4
Qadir: -190.79999999999998
Mahnaz: 1232.2
Example 3
Following is an example showing how Map.Entry can be used to get key of a map entry −
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
public class HashMapDemo {
public static void main(String args[]) {
// Create a hash map
HashMap<String, Double> hm = new HashMap<>();
// Put elements to the map
hm.put("Zara", Double.valueOf(3434.34));
hm.put("Mahnaz", Double.valueOf(123.22));
hm.put("Ayan", Double.valueOf(1378.00));
hm.put("Daisy", Double.valueOf(99.22));
hm.put("Qadir", Double.valueOf(-19.08));
// Get a set of the entries
Set<Map.Entry<String, Double>> set = hm.entrySet();
// Get an iterator
Iterator<Map.Entry<String, Double>> i = set.iterator();
// Display elements
while(i.hasNext()) {
Map.Entry<String, Double> me = i.next();
System.out.println(me.getKey());
}
}
}
Output
Daisy
Ayan
Zara
Qadir
Mahnaz
java_collections.htm
