HashTable putIfAbsent() method in Java with Examples
Last Updated :
30 Sep, 2019
The putIfAbsent(Key, value) method of Hashtable class which allows to map a value to a given key if given key is not associated with a value or mapped to null. A null value is returned if such key-value set is already present in the HashMap.
Syntax:
public V putIfAbsent(K key, V value)
Parameters: This method accepts two parameters:
- key: specifies the key to which the specified value is to be mapped if key is not associated with any value.
- value: specifies the value to be mapped to the specified key.
Returns: This method returns the existing value mapped to the key and returns null if no value is previously mapped to the key.
Exception: This method throws:
- NullPointerException: when the specified parameters are null.
Below programs illustrate the putIfAbsent(Key, value) method:
Program 1:
import java.util.*;
public class GFG {
public static void main(String[] args)
{
Map<String, Integer>
table = new Hashtable<>();
table.put("Pen", 10);
table.put("Book", 500);
table.put("Clothes", 400);
table.put("Mobile", 5000);
System.out.println("hashTable: "
+ table.toString());
String retValue
= String.valueOf(table
.putIfAbsent("Booklet", 2500));
System.out.println("Returned value "
+ "for Key 'Booklet' is: "
+ retValue);
System.out.println("hashTable: "
+ table);
retValue
= String.valueOf(table
.putIfAbsent("Book", 4500));
System.out.println("Returned value"
+ " for key 'Book' is: "
+ retValue);
System.out.println("hashTable: "
+ table);
}
}
|
Output:
hashTable: {Book=500, Mobile=5000, Pen=10, Clothes=400}
Returned value for Key 'Booklet' is: null
hashTable: {Book=500, Mobile=5000, Pen=10, Clothes=400, Booklet=2500}
Returned value for key 'Book' is: 500
hashTable: {Book=500, Mobile=5000, Pen=10, Clothes=400, Booklet=2500}
Program 2: To Show NullPointerException
import java.util.*;
public class GFG {
public static void main(String[] args)
{
Map<Integer, String>
table = new Hashtable<>();
table.put(1, "100RS");
table.put(2, "500RS");
table.put(3, "1000RS");
System.out.println("hashTable: "
+ table.toString());
try {
table.putIfAbsent(null, "8");
}
catch (NullPointerException e) {
System.out.println("Exception: " + e);
}
}
}
|
Output:
hashTable: {3=1000RS, 2=500RS, 1=100RS}
Exception: java.lang.NullPointerException
References: https://docs.oracle.com/javase/8/docs/api/java/util/Hashtable.html#putIfAbsent-K-V-
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