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Cara Menghapus elemen yang kedaluwarsa dari HashMap dan Menambahkan lebih banyak elemen secara bersamaan – Java Timer, TimerTask, dan futures() – Contoh Lengkap

Diterbitkan: 2021-04-02
Cara Menghapus elemen kedaluwarsa dari HashMap dan Menambahkan lebih banyak elemen pada Saat yang Sama - Java Timer, TimerTask, dan futures()

Hashmap, ArrayList, Static Map, Vektor, dll adalah elemen kerangka kerja koleksi Java yang paling banyak digunakan. Ada banyak skenario yang dapat Anda gunakan sesuai kebutuhan Anda.

Contoh ini adalah Contoh Java yang sangat menarik. Kami akan melakukan operasi di bawah ini pada HashMap() tunggal.

  • Buat Objek crunchifyMap
  • Terus tambahkan elemen ke Peta setiap detik yang waktu kedaluwarsanya diatur ke 5 seconds
  • Check elemen kedaluwarsa seperti cache setiap detik dan delete from map if expired
  • Setelah 5 detik, Anda akan always same size dan always 5 elements saat Anda menambahkan dan menghapus elemen yang kedaluwarsa setiap detik

Juga jika Anda memiliki below questions ini maka Anda berada di tempat yang tepat:

  • Apa itu Contoh Peta Kedaluwarsa Pasif
  • Peta Bersamaan dengan elemen waktu habis
  • Contoh Peta Cache Java
  • Contoh Java TimerTask
  • Evictor – Contoh Peta Konkuren Java

Mari kita mulai:

Poin-1

  • Buat elemen Timer crunchifyTimer
  • Menjadwalkan tugas yang ditentukan CrunchifyReminder() untuk eksekusi penundaan tetap yang berulang yaitu 1 detik
  • Dalam tugas terjadwal
    • add elemen ke crunchifyMap
    • periksa elemen kedaluwarsa dari crunchifyMap dan hapus

Poin-2

  • Selama operasi addElement()
    • Kami mengasosiasikan current time untuk setiap elemen
  • Selama operasi crunchifyClearExipredElementsFromMap()
    • Kami memeriksa waktu saat ini dengan waktu elemen
    • Jika perbedaan waktu lebih dari 5 detik maka hapus saja elemen dari crunchifyMap

Poin-3

  • Selama menambah dan menghapus elemen cetak operasi di konsol Eclipse
  • Elemen yang ditambahkan ke-1 akan dihapus ke-1 dan seterusnya
  • Silakan periksa keluaran konsol Eclipse untuk hasilnya

Berikut adalah program Javanya:

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package crunchify . com . tutorials ;
 
import java . util . ArrayList ;
import java . util . Date ;
import java . util . HashMap ;
import java . util . Iterator ;
import java . util . Map ;
import java . util . Map . Entry ;
import java . util . Timer ;
import java . util . TimerTask ;
 
/**
* @author Crunchify.com
* <p>
* - Keep adding element to Map every second which has expire time set to 5 seconds
* - Check for expired element every second and delete from map if expired
* - After 5 seconds you will get always same size as you are adding and deleting expired elements every second
*/
 
public class CrunchifyCleanExipredMapElements {
Timer crunchifyTimer ;
private static final long EXPIRED_TIME_IN_SEC = 5L ;
private static final Map < Double , ArrayList < Date > > crunchifyMap = new HashMap < > ( ) ;
public static void main ( String [ ] args ) {
new CrunchifyCleanExipredMapElements ( 1 ) ;
crunchifyLog ( "Start Adding element every second\n\n" ) ;
}
public CrunchifyCleanExipredMapElements ( int seconds ) {
// Timer() - Creates a new timer. The associated thread does not run as a daemon.
crunchifyTimer = new Timer ( ) ;
// Schedules the specified task for repeated fixed-delay execution
// schedule(): Schedules the specified task for repeated fixed-delay execution, beginning after the specified delay.
// Subsequent executions take place at approximately regular intervals separated by the specified period.
// In fixed-delay execution, each execution is scheduled relative to the actual execution time of the previous execution.
// If an execution is delayed for any reason (such as garbage collection or other background activity), subsequent executions will be delayed as well.
// In the long run, the frequency of execution will generally be slightly lower than the reciprocal of the specified period (assuming the system clock underlying Object.wait(long) is accurate).
crunchifyTimer . schedule ( new CrunchifyReminder ( ) , 0 , seconds * 1000L ) ;
}
// TimeTask: A task that can be scheduled for one-time or repeated execution by a Timer.
// A timer task is not reusable. Once a task has been scheduled for execution on a Timer or cancelled,
// subsequent attempts to schedule it for execution will throw IllegalStateException.
class CrunchifyReminder extends TimerTask {
public void run ( ) {
// We are checking for expired element from map every second
crunchifyClearExpiredElementsFromMap ( ) ;
// We are adding element every second
addElement ( ) ;
}
}
public void addElement ( ) {
crunchifyAddElementToMap ( Math . random ( ) ) ;
}
// Check for element's expired time. If element is > 5 seconds old then remove it
private static void crunchifyClearExpiredElementsFromMap ( ) {
// Date() - Allocates a Date object and initializes it so that it represents the time at which it was allocated, measured to the nearest millisecond.
Date currentTime = new Date ( ) ;
Date actualExpiredTime = new Date ( ) ;
// if element time stamp and current time stamp difference is 5 second then delete element
actualExpiredTime . setTime ( currentTime . getTime ( ) - EXPIRED_TIME_IN_SEC * 1000L ) ;
// size() - Returns the number of key-value mappings in this map. If the map contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.
System . out . println ( "crunchifyMap size:" + CrunchifyCleanExipredMapElements . crunchifyMap . size ( ) ) ;
Iterator < Entry < Double , ArrayList < Date > > > crunchifyIterator = CrunchifyCleanExipredMapElements . crunchifyMap . entrySet ( ) . iterator ( ) ;
// hasNext() - Returns true if the iteration has more elements. (In other words, returns true if next would return an element rather than throwing an exception.)
while ( crunchifyIterator . hasNext ( ) ) {
// next() - Returns the next element in the iteration.
Entry < Double , ArrayList < Date > > entry = crunchifyIterator . next ( ) ;
// getValue() - Returns the value corresponding to this entry.
// If the mapping has been removed from the backing map (by the iterator's remove operation), the results of this call are undefined.
ArrayList < Date > crunchifyElement = entry . getValue ( ) ;
while ( crunchifyElement . size ( ) > 0
&& crunchifyElement.get(0).compareTo(actualExpiredTime) < 0) {
crunchifyLog("----------- Expired Element Deleted: " + entry.getKey());
crunchifyElement . remove ( 0 ) ;
}
if ( crunchifyElement . size ( ) == 0 ) {
// remove() - Removes from the underlying collection the last element returned by this iterator (optional operation).
// This method can be called only once per call to next.
crunchifyIterator . remove ( ) ;
}
}
}
// Adding new element to map with current timestamp
private static void crunchifyAddElementToMap ( Double digit ) {
ArrayList < Date > crunchifyList = new ArrayList < > ( ) ;
CrunchifyCleanExipredMapElements . crunchifyMap . put ( digit , crunchifyList ) ;
// add() - Appends the specified element to the end of this list.
crunchifyList . add ( new Date ( ) ) ;
crunchifyLog ( "+++++++++++ Add Element:" + digit + "\n" ) ;
}
private static void crunchifyLog ( String string ) {
System . out . println ( string ) ;
}
}
 

Keluaran Konsol Eclipse:

Jalankan saja program di atas dan Anda akan melihat hasilnya seperti di bawah ini.

Cara Menghapus elemen yang kedaluwarsa dari HashMap dan Menambahkan lebih banyak elemen secara bersamaan - Java Timer, TimerTask, dan futures() - Hasil Konsol
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Start Adding element every second
crunchifyMap size : 0
+++++++++++ Add Element : 0.6970683199424504
crunchifyMap size : 1
+++++++++++ Add Element : 0.8103548990859972
crunchifyMap size : 2
+++++++++++ Add Element : 0.849973176897403
crunchifyMap size : 3
+++++++++++ Add Element : 0.2770459184269851
crunchifyMap size : 4
+++++++++++ Add Element : 0.9136028332849369
crunchifyMap size : 5
----------- Expired Element Deleted : 0.6970683199424504
+++++++++++ Add Element : 0.6630362698520832
crunchifyMap size : 5
----------- Expired Element Deleted : 0.8103548990859972
+++++++++++ Add Element : 0.38906826918659854
crunchifyMap size : 5
----------- Expired Element Deleted : 0.849973176897403
+++++++++++ Add Element : 0.3997935729434138
crunchifyMap size : 5
----------- Expired Element Deleted : 0.2770459184269851
+++++++++++ Add Element : 0.20373441843273887
 
Process finished with exit code 130 ( interrupted by signal 2 : SIGINT )

Beri tahu saya jika Anda menghadapi masalah saat menjalankan program Java di atas.