Intern.java

// Concurrent canonicalizing map atop ConcurrentMap - Pages 273-274
package org.effectivejava.examples.chapter10.item69;

import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

public class Intern {
	private static final ConcurrentMap<String, String> map = new ConcurrentHashMap<String, String>();

	// Concurrent canonicalizing map atop ConcurrentMap - not optimal - Page 273
	// public static String intern(String s) {
	// String previousValue = map.putIfAbsent(s, s);
	// return previousValue == null ? s : previousValue;
	// }

	// Concurrent canonicalizing map atop ConcurrentMap - faster! - Page 274
	public static String intern(String s) {
		String result = map.get(s);
		if (result == null) {
			result = map.putIfAbsent(s, s);
			if (result == null)
				result = s;
		}
		return result;
	}
}