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  1. import java.util.*;
  2. import java.lang.*;
  3. import java.io.*;
  4.  
  5. import java.util.function.Supplier;
  6.  
  7. class Ideone
  8. {
  9.  
  10.  
  11. @FunctionalInterface
  12. public interface Lazy<T> extends Supplier<T> {
  13.     abstract class Cache {
  14.         private volatile static Map<Integer, Object> instances = new HashMap<>();
  15.  
  16.         private static synchronized Object getInstance(int instanceId, Supplier<Object> create) {
  17.  
  18.             Object instance = instances.get(instanceId);
  19.             if (instance == null) {
  20.                 synchronized (Cache.class) {
  21.                     instance = instances.get(instanceId);
  22.                     if (instance == null) {
  23.                         instance = create.get();
  24.                         instances.put(instanceId, instance);
  25.                     }
  26.                 }
  27.             }
  28.             return instance;
  29.         }
  30.     }
  31.  
  32.     @Override
  33.     default T get() {
  34.         return (T) Cache.getInstance(this.hashCode(), () -> init());
  35.     }
  36.  
  37.     T init();
  38. }
  39.  
  40.  
  41. 	static Lazy<String> name1 = () -> { 
  42. 		System.out.println("lazy init 1"); 
  43. 		return "name 1";
  44. 	};
  45.  
  46. 	static Lazy<String> name2 = () -> { 
  47. 		System.out.println("lazy init 2"); 
  48. 		return "name 2";
  49. 	};
  50.  
  51.  
  52. 	public static void main (String[] args) throws java.lang.Exception
  53. 	{
  54. 		System.out.println("start"); 
  55. 		System.out.println(name1.get());
  56. 		System.out.println(name1.get());
  57. 		System.out.println(name2.get());
  58. 		System.out.println(name2.get());
  59. 		System.out.println("end"); 
  60. 	}
  61.  
  62. }
Success #stdin #stdout 0.22s 320704KB
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stdin
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Standard input is empty
stdout
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start
lazy init 1
name 1
name 1
lazy init 2
name 2
name 2
end
https://ideone.com/3b9alx
language:
Java (HotSpot 12)
created:
8 years ago
visibility:
public

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