Insider's blog.: 09/16/14

вторник, 16 сентября 2014 г.

Multiton - registry of singletons
http://en.wikipedia.org/wiki/Multiton_pattern

<<

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

	public class FooMultiton {
	private static final Map<Object, FooMultiton> instances = new HashMap<Object, FooMultiton>();

	private FooMultiton() {
	// no explicit implementation
	}

	public static synchronized FooMultiton getInstance(Object key) {

	// Our "per key" singleton
	FooMultiton instance = instances.get(key);

	if (instance == null) {
	// Lazily create instance
	instance = new FooMultiton();

	// Add it to map
	instances.put(key, instance);
	}

	return instance;
	}

	// other fields and methods ...
	}

view raw FooMultiton.java hosted with ❤ by GitHub

	import junit.framework.*;

	final class LazySingleton {
	private int i;
	private static class LazySingletonLoader {
	private static final LazySingleton INSTANCE = new LazySingleton();
	}
	private LazySingleton() {
	if (LazySingletonLoader.INSTANCE != null) {
	throw new IllegalStateException("Already instantiated");
	}
	}
	public static LazySingleton getReference() {
	return LazySingletonLoader.INSTANCE;
	}
	public int getValue() { return i; }
	public void setValue(int x) { i = x; }
	}

	public class LazySingletonPattern extends TestCase {
	public void test() {
	LazySingleton s = LazySingleton.getReference();
	String result = "" + s.getValue();
	System.out.println(result);
	assertEquals(result, "0");
	LazySingleton s2 = LazySingleton.getReference();
	s2.setValue(9);
	result = "" + s.getValue();
	System.out.println(result);
	assertEquals(result, "9");
	try {
	// Can't do this: compile-time error.
	// LazySingleton s3 = (LazySingleton)s2.clone();
	} catch(Exception e) {
	throw new RuntimeException(e);
	}
	}
	public static void main(String[] args) {
	junit.textui.TestRunner.run(LazySingletonPattern.class);
	}
	}