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Utility classes are classes that only include static members and are not
designed to be instantiated, for example `java.lang.Math` or `java.util.Arrays`.
In the absence of explicit constructors, however, the compiler provides a
public, parameterless default constructor. To a user, this constructor is
indistinguishable from any other. It is not uncommon for a published API to
accidentally include a public constructor for a class intended to be
uninstantiable.
To prevent users from instantiating classes that are not designed to be
instantiated, you can add a private constructor:
```java
public class UtilityClass {
private UtilityClass() {}
}
```
See:
* [Effective Java 3rd Edition ยง4][ej3e-4]
[ej3e-4]: https://books.google.com/books?id=BIpDDwAAQBAJ
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