019: Effective Java for Android developers : Item 4

Singer and Android developer Donn Felker explores Joshua Bloch's fourth Item: Enforce noninstantiability with a private constructor.

Stay tuned, cause we got more of these quick ones coming.

• Effective Java (2nd Edition) - Joshua Bloch

Enforce noninstantiability with a private constructor.

Examples where you don't want class to be instantiated

1. class that groups static methods and static fields (Util like classes think java.lang.Math/java.util.Arrays)
2. class that groups static methods (including factory methods) for objects implementing specific interfaces (think java.util.Collections)
3. class that group methods on a final class (vs. extending the class)

Considerations

• Makes no sense to instantiate such "Util" classes
• Private constructors prevent instantiation
• Important side effect: prevents subclassing

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