Immutable objects
- Objects consider immutable if its state cannot change after it is constructed.
- Don't provide "setter" methods — methods that modify fields or objects referred to by fields.
- Make all fields final and private.
- Don't allow subclasses to override methods. The simplest way to do this is to declare the class as final. A more sophisticated approach is to make the constructor private and construct instances in factory methods.
- If the instance fields include references to mutable objects, don't allow those objects to be changed:
- Don't provide methods that modify the mutable objects.
- Don't share references to the mutable objects.
- Never store references to external, mutable objects passed to the constructor; if necessary, create copies, and store references to the copies. Similarly, create copies of your internal mutable objects when necessary to avoid returning the originals in your methods.
- Objects consider immutable if its state cannot change after it is constructed.
- Don't provide "setter" methods — methods that modify fields or objects referred to by fields.
- Make all fields final and private.
- Don't allow subclasses to override methods. The simplest way to do this is to declare the class as final. A more sophisticated approach is to make the constructor private and construct instances in factory methods.
- If the instance fields include references to mutable objects, don't allow those objects to be changed:
- Don't provide methods that modify the mutable objects.
- Don't share references to the mutable objects.
- Never store references to external, mutable objects passed to the constructor; if necessary, create copies, and store references to the copies. Similarly, create copies of your internal mutable objects when necessary to avoid returning the originals in your methods.
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In Java Strings are immutable
In Java, Strings are immutable.
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