Effective Java 04 Enforce noninstantiability with a private constructor

A class can be made noninstantiable by including a private constructor.

// Noninstantiable utility class

public class UtilityClass {

// Suppress default constructor for noninstantiability

private UtilityClass() {

throw new AssertionError();

}

... // Remainder omitted

}

Advantage:

This explicitly prevents the user to instantiate the class.

Disadvantage:

The class cannot be subclassed.

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原文：http://www.cnblogs.com/haokaibo/p/3570407.html