Java Hashtable put() Method Last Updated : 22 May, 2025 Comments Improve Suggest changes Like Article Like Report The Hashtable.put() method is a part of java.util package. This method is used to insert a mapping into a table. This means we can insert a specific key and the value it maps to into a particular table. If an existing key is passed, then the previous value gets replaced by the new value. If a new pair is passed, then the pair gets inserted as a whole.Syntax of Hashtable put() MethodBelow is the syntax of put() method.Hash_Table.put(key, value)Parameters:This method takes two parameters, both of the Object type of the Hashtable.key: This refers to the key element that needs to be inserted into the table for mapping.value: This refers to the value that the above key will map to.Return Value: If an existing key is passed, the previous value gets returned. If a new pair is passed, then null is returned.Examples of Java Hashtable put() MethodExample 1: In this example, we are going to use the put() method when an existing key is passed. Java // Java program to demonstrate Hashtable.put() method import java.util.*; public class Geeks { public static void main(String[] args) { // Create an empty Hashtable Hashtable<Integer, String> ht = new Hashtable<Integer, String>(); // Insert values into the Hashtable ht.put(10, "Geeks"); ht.put(15, "4"); ht.put(20, "Geeks"); ht.put(25, "Welcomes"); ht.put(30, "You"); System.out.println("Initial table is: " + ht); // Insert existing key along with a new value String returned = ht.put(20, "All"); // Verify the returned value System.out.println("Returned value is: " + returned); System.out.println("New table is: " + ht); } } Example 2: In this example, let's use the put() method when a new key is passed and we will see what it prints. Java // Java program to demonstrate Hashtable.put() method import java.util.*; public class Geeks { public static void main(String[] args) { // Create an empty Hashtable Hashtable<Integer, String> ht = new Hashtable<Integer, String>(); // Insert values into the Hashtable ht.put(10, "Geeks"); ht.put(15, "4"); ht.put(20, "Geeks"); ht.put(25, "Welcomes"); ht.put(30, "You"); System.out.println("Initial table is: " + ht); // Insert new key along with a value String returned = ht.put(50, "All"); // Verify the returned value System.out.println("Returned value is: " + returned); System.out.println("New table is: " + ht); } } Important Points:The put() method replaces the value if the key is already exists.The method returns the previous value associated with the key or it returns null if the key was not present.This method works with any combination of data types as the key and value. Comment More infoAdvertise with us Next Article Java Hashtable get() Method C chinmoy lenka Follow Improve Article Tags : Java Java-Collections Java-HashTable Practice Tags : JavaJava-Collections Similar Reads Hashtable in Java Hashtable class, introduced as part of the Java Collections framework, implements a hash table that maps keys to values. Any non-null object can be used as a key or as a value. To successfully store and retrieve objects from a hashtable, the objects used as keys must implement the hashCode method an 12 min read HashTable forEach() method in Java with Examples The forEach(BiConsumer) method of Hashtable class perform the BiConsumer operation on each entry of hashtable until all entries have been processed or the action throws an exception. The BiConsumer operation is a function operation of key-value pair of hashtable performed in the order of iteration. 2 min read Hashtable computeIfAbsent() method in Java with Examples The computeIfAbsent(Key, Function) method of Hashtable class which allows you to compute value of a mapping for specified key if key is not already associated with a value (or is mapped to null). If mapping function of this method returns null, then no mapping is recorded. If the remapping function 2 min read HashTable putIfAbsent() method in Java with Examples 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: T 2 min read Java Hashtable put() Method The Hashtable.put() method is a part of java.util package. This method is used to insert a mapping into a table. This means we can insert a specific key and the value it maps to into a particular table. If an existing key is passed, then the previous value gets replaced by the new value. If a new pa 2 min read Java Hashtable get() Method The Hashtable.get() method is a built-in method of the java.util.Hashtable class. This method is used to retrieve or fetch the value mapped by a particular key mentioned in the parameter. It returns NULL when the table contains no such mapping for the key. In this article, we will learn about the Ha 3 min read Java Hashtable isEmpty() Method The Hashtable.isEmpty() method is a built-in method of the java.util.Hashtable class. This method is used to check if the table is empty or not. The method returns true, if no key-value pair or mapping is present in the table, else it returns false.Syntax of Hashtable isEmpty() Methodhash_table.isEm 2 min read Hashtable size() Method in Java The java.util.Hashtable.size() method of Hashtable class is used to get the size of the table which refers to the number of the key-value pair or mappings in the Table. Syntax: Hash_Table.size() Parameters: The method does not take any parameters. Return Value: The method returns the size of the tab 2 min read Hashtable remove() Method in Java The java.util.Hashtable.remove() is an inbuilt method of Hashtable class and is used to remove the mapping of any particular key from the table. It basically removes the values for any particular key in the Table.Syntax: Hash_Table.remove(Object key) Parameters: The method takes one parameter key wh 2 min read Hashtable keys() Method in Java As we all know enumeration defines java class type so do enumerations can have constructors, methods, and instance variables. The java.util.Hashtable.keys() method of Hashtable class in Java is used to get the enumeration of the keys present in the hashtable. Illustration: Syntax: public Enumeration 2 min read Like