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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.*;
  4. import java.lang.*;
  5. import java.io.*;
  6.  
  7. /* Name of the class has to be "Main" only if the class is public. */
  8. class Ideone
  9. {
  10. 	public static void main (String[] args) throws java.lang.Exception
  11. 	{
  12.  
  13.  
  14.         Set < UUID > set =
  15.                 Collections.synchronizedSet(
  16.                         Collections.newSetFromMap(
  17.                                 new WeakHashMap <>()
  18.                         )
  19.                 );
  20.  
  21.         UUID uuid1 = UUID.fromString( "a8ee1e34-cead-11e8-a8d5-f2801f1b9fd1" );
  22.         UUID uuid2 = UUID.fromString( "39bda2b4-5885-4f56-a900-411a49beebac" );
  23.         UUID uuid3 = UUID.fromString( "0b630385-0452-4b96-9238-20cdce37cf55" );
  24.         UUID uuid4 = UUID.fromString( "98d2bacf-3f7f-4ea0-9c17-c91f6702322c" );
  25.  
  26.         System.out.println( "Size before adding: " + set.size() );
  27.  
  28.         set.add( uuid1 );
  29.         set.add( uuid2 );
  30.         set.add( uuid3 );
  31.         set.add( uuid4 );
  32.  
  33.         System.out.println( "Size after adding 4 items: " + set.size() );  // Expect 4.
  34.  
  35.         set.remove( uuid3 );
  36.  
  37.         System.out.println( "Size after removing item # 3: " + set.size() );  // Expect 3.
  38.  
  39.         uuid2 = null;  // Release that UUID to garbage-collection.
  40.         // System.gc(); // Ask the JVM to run the garbage-collection. Only a suggestion, may be ignored.
  41.         // try {
  42.         //     Thread.sleep( 1_000 );  // Wait a moment, just for the heck of it.
  43.         // } catch ( InterruptedException e ) {
  44.         //     e.printStackTrace();
  45.         // }
  46.  
  47.         System.out.println( "Size after making garbage of item # 2: " + set.size() );  // Expect 2.
  48.  
  49. 	}
  50. }
Success #stdin #stdout 0.08s 2184192KB
comments (?)
stdin 
Standard input is empty
stdout 
Size before adding: 0
Size after adding 4 items: 4
Size after removing item # 3: 3
Size after making garbage of item # 2: 3
https://ideone.com/JAs936
language:
Java (HotSpot 12)
created:
7 years ago
visibility:
public

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