PHA PHA - 3 months ago 27
Java Question

iterate through a hashmap 'in chunks'

I need to iterate through a hashmap with 5000 items but after iterating on 500th item I need to do a sleep and then continue the next 500 items. Here is the example stolen from here. Any help would appreciated.

import java.util.HashMap;
import java.util.Map;

public class HashMapExample {

public static void main(String[] args) {
Map vehicles = new HashMap();

// Add some vehicles.
vehicles.put("BMW", 5);
vehicles.put("Mercedes", 3);
vehicles.put("Audi", 4);
vehicles.put("Ford", 10);
// add total of 5000 vehicles

System.out.println("Total vehicles: " + vehicles.size());

// Iterate over all vehicles, using the keySet method.
// here are would like to do a sleep iterating through 500 keys
for(String key: vehicles.keySet())
System.out.println(key + " - " + vehicles.get(key));
System.out.println();

String searchKey = "Audi";
if(vehicles.containsKey(searchKey))
System.out.println("Found total " + vehicles.get(searchKey) + " "
+ searchKey + " cars!\n");

// Clear all values.
vehicles.clear();

// Equals to zero.
System.out.println("After clear operation, size: " + vehicles.size());
}
}

Answer

Just have a counter variable to keep track of the number of iterations so far:

int cnt = 0;
for(String key: vehicles.keySet()) {
  System.out.println(key + " - " + vehicles.get(key));

  if (++cnt % 500 == 0) {
    Thread.sleep(sleepTime);  // throws InterruptedException; needs to be handled.
  }
}

Note that if you want both key and value in a loop, it is better to iterate the map's entrySet():

for(Map.Entry<String, Integer> entry: vehicles.entrySet()) {
  String key = entry.getKey();
  Integer value = entry.getValue();
  // ...
}

Also: don't use raw types:

Map<String, Integer> vehicles = new HashMap<>();
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