WeakHashMap

WeakHashMap provides a Map based on weakly reachable keys. The key is removed from the map after the garbage collector clears all weak references to the key.

The following code provides a simple demonstration of the WeakHashMap class.

 
import java.util.Map;
import java.util.WeakHashMap;

class LargeObject {
  private byte[] memory = new byte[1024 * 1024 * 50]; // 50 megabytes
}

public class Main {
  public static void main(String[] args) {
    Map<LargeObject, String> map = new WeakHashMap<LargeObject, String>();
    LargeObject lo = new LargeObject();
    map.put(lo, "Large Object");
    System.out.println(map);
    lo = null;
    while (!map.isEmpty()) {
      System.gc();
    }
    System.out.println(map);
  }
}

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