- Java.util Package Classes
- Java.util - Home
- Java.util - ArrayDeque
- Java.util - ArrayList
- Java.util - Arrays
- Java.util - BitSet
- Java.util - Calendar
- Java.util - Collections
- Java.util - Currency
- Java.util - Date
- Java.util - Dictionary
- Java.util - EnumMap
- Java.util - EnumSet
- Java.util - Formatter
- Java.util - GregorianCalendar
- Java.util - HashMap
- Java.util - HashSet
- Java.util - Hashtable
- Java.util - IdentityHashMap
- Java.util - LinkedHashMap
- Java.util - LinkedHashSet
- Java.util - LinkedList
- Java.util - ListResourceBundle
- Java.util - Locale
- Java.util - Observable
- Java.util - PriorityQueue
- Java.util - Properties
- Java.util - PropertyPermission
- Java.util - PropertyResourceBundle
- Java.util - Random
- Java.util - ResourceBundle
- Java.util - ResourceBundle.Control
- Java.util - Scanner
- Java.util - ServiceLoader
- Java.util - SimpleTimeZone
- Java.util - Stack
- Java.util - StringTokenizer
- Java.util - Timer
- Java.util - TimerTask
- Java.util - TimeZone
- Java.util - TreeMap
- Java.util - TreeSet
- Java.util - UUID
- Java.util - Vector
- Java.util - WeakHashMap
- Java.util Package Extras
- Java.util - Interfaces
- Java.util - Exceptions
- Java.util - Enumerations
- Java.util Useful Resources
- Java.util - Useful Resources
- Java.util - Discussion
Java Hashtable keySet() Method
Description
The Java Hashtable keySet() method is used to get a Set view of the keys contained in this Hashtable.
Declaration
Following is the declaration for java.util.Hashtable.keySet() method.
public Set<K> keySet()
Parameters
NA
Return Value
The method call returns a set view of the keys contained in this map.
Exception
NA
Getting Set of Keys of a HashTable of Integer, Integer Pair Example
The following example shows the usage of Java Hashtable keySet() method to get a Set view of keys of a Hashtable. We've created a Hashtable object of Integer,Integer pairs. Then few entries are added, table is printed. Using keySet() method, set is retrieved and printed.
package com.tutorialspoint; import java.util.Hashtable; public class HashtableDemo { public static void main(String args[]) { // create hash table Hashtable<Integer,Integer> hashtable = new Hashtable<>(); // populate hash table hashtable.put(1, 1); hashtable.put(2, 2); hashtable.put(3, 3); System.out.println("Initial table elements: " + hashtable); System.out.println("Key Set: " + hashtable.keySet()); } }
Output
Let us compile and run the above program, this will produce the following result.
Initial table elements: {3=3, 2=2, 1=1} Key Set: [3, 2, 1]
Getting Set of Keys of a HashTable of Integer, String Pair Example
The following example shows the usage of Java Hashtable keySet() method to get a Set view of keys of a Hashtable. We've created a Hashtable object of Integer,String pairs. Then few entries are added, table is printed. Using keySet() method, set is retrieved and printed.
package com.tutorialspoint; import java.util.Hashtable; public class HashtableDemo { public static void main(String args[]) { // create hash table Hashtable<Integer,String> hashtable = new Hashtable<>(); // populate hash table hashtable.put(1, "tutorials"); hashtable.put(2, "point"); hashtable.put(3, "is best"); System.out.println("Initial table elements: " + hashtable); System.out.println("Key Set: " + hashtable.keySet()); } }
Output
Let us compile and run the above program, this will produce the following result.
Initial table elements: {3=is best, 2=point, 1=tutorials} Key Set: [3, 2, 1]
Getting Set of Keys of a HashTable of Integer, Object Pair Example
The following example shows the usage of Java Hashtable keySet() method to get a Set view of keys of a Hashtable. We've created a Hashtable object of Integer,Student pairs. Then few entries are added, table is printed. Using keySet() method, set is retrieved and printed.
package com.tutorialspoint; import java.util.Hashtable; public class HashtableDemo { public static void main(String args[]) { // create hash table Hashtable<Integer,Student> hashtable = new Hashtable<>(); // populate hash table hashtable.put(1, new Student(1, "Julie")); hashtable.put(2, new Student(2, "Robert")); hashtable.put(3, new Student(3, "Adam")); System.out.println("Initial table elements: " + hashtable); System.out.println("Key Set view: " + hashtable.keySet()); } } class Student { int rollNo; String name; Student(int rollNo, String name){ this.rollNo = rollNo; this.name = name; } @Override public String toString() { return "[ " + this.rollNo + ", " + this.name + " ]"; } }
Output
Let us compile and run the above program, this will produce the following result.
Initial table elements: {3=[ 3, Adam ], 2=[ 2, Robert ], 1=[ 1, Julie ]} Key Set view: [3, 2, 1]
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