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  1. import lombok.Getter;
  2. import lombok.SneakyThrows;
  3.  
  4. @Getter // Lombok annotation to generate getter methods for the fields
  5. class Database {
  6.     private static Database database;
  7.     private final String connection;
  8.  
  9.     private Database(String connection) {
  10.         this.connection = connection;
  11.     }
  12.  
  13.     @SneakyThrows // Lombok annotation to handle checked exceptions
  14.     public static synchronized Database getInstance(String connection) {
  15.         System.out.printf("Thread %s entered a critical section\n", Thread.currentThread().getName());
  16.  
  17.         if (database == null) {
  18.             System.out.printf("Thread %s initializing the database instance\n", Thread.currentThread().getName());
  19.  
  20.             Thread.sleep(1000); // Simulate resource-intensive initialization
  21.             database = new Database(connection);
  22.         }
  23.  
  24.         System.out.printf("Thread %s returns...\n", Thread.currentThread().getName());
  25.  
  26.         return database;
  27.     }
  28. }
  29.  
  30. public class Main {
  31.     public static void main(String[] args) throws InterruptedException {
  32.         // Create two threads that attempt to access the singleton instance
  33.  
  34.         new Thread(() -> {
  35.             Database.getInstance("Dummy connection string of " + Thread.currentThread().getName());
  36.         }).start();
  37.  
  38.         new Thread(() -> {
  39.             Database.getInstance("Dummy connection string of " + Thread.currentThread().getName());
  40.         }).start();
  41.  
  42.         // Allow some time for threads to complete their execution
  43.         Thread.sleep(2000);
  44.  
  45.         // Retrieve the connection from the singleton instance and log the result
  46.         String finalConnection = Database.getInstance(null).getConnection();
  47.         System.out.printf("Database connection: %s\n", finalConnection);
  48.     }
  49. }
  50.  
  51. /*
  52.  
  53. Output without synchronized:
  54.  
  55. Thread Thread-1 entered a critical section
  56. Thread Thread-1 initializing the database instance
  57. Thread Thread-0 entered a critical section
  58. Thread Thread-0 initializing the database instance
  59. Thread main entered a critical section
  60. Database connection: dummy_connection of Thread-1
  61.  
  62. Output with synchronized:
  63. Thread Thread-1 entered a critical section
  64. Thread Thread-1 initializing the database instance
  65. Thread Thread-0 entered a critical section
  66. Thread main entered a critical section
  67. Database connection: Dummy connection string of Thread-1
  68. */
Compilation error #stdin compilation error #stdout 0s 0KB
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Standard input is empty
compilation info 
Main.java:1: error: package lombok does not exist
import lombok.Getter;
             ^
Main.java:2: error: package lombok does not exist
import lombok.SneakyThrows;
             ^
Main.java:4: error: cannot find symbol
@Getter // Lombok annotation to generate getter methods for the fields
 ^
  symbol: class Getter
Main.java:13: error: cannot find symbol
    @SneakyThrows // Lombok annotation to handle checked exceptions
     ^
  symbol:   class SneakyThrows
  location: class Database
Main.java:46: error: cannot find symbol
        String finalConnection = Database.getInstance(null).getConnection();
                                                           ^
  symbol:   method getConnection()
  location: class Database
5 errors
stdout
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Standard output is empty
https://ideone.com/6j9ejR
language:
Java (HotSpot 12)
created:
1 year ago
visibility:
public

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