EJ-21 Use Function Objects to Represent Strategies

Ref: Effective Java by Joshua Bloch

Strategy classes are often declered using anonymous classes and pessed to target operation. The following statement sorts an array of strings according to length:

	Arrays.sort(stringArray, new Comparator<String>() {
	public int compare(String s1, String s2) {
	return s1.length() - s2.length();
	}
	});

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But note that using an anonymous class in this way will create a new instance each time the call is executed. When it is expected for repeated use, it is generally implemented as a private static member class and exported in a public static final field whose type is the strategy interface

	// Exporting a concrete strategy
	class Host {
	private static class StrLenCmp
	implements Comparator<String>, Serializable {
	public int compare(String s1, String s2) {
	return s1.length() - s2.length();
	}
	}
	// Returned comparator is serializable
	public static final Comparator<String>
	STRING_LENGTH_COMPARATOR = new StrLenCmp();
	... // Bulk of class omitted
	}

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