Important Points about Interface in Java

客官°小女子只卖身不卖艺 2024-03-25 09:47 52阅读 0赞

### Important Points about Interface in Java ###

1.  `interface` is the code that is used to create an interface in java.

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1.  Interfaces `can’t have constructors` because we can’t instantiate them and interfaces can’t have a method with body.
2.  We `can’t instantiate an interface` in java.

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1.  Interface [provides][] `absolute abstraction`, abstract classes in java to provide abstraction but abstract classes can have method implementations but interface can’t.
2.  All the methods in an interface are [implicitly][] `abstract` unless the interface methods are static or default. `Static methods` and `default methods` in interfaces are added in Java 8, for more details read Java 8 interface changes.

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1.  By default any `attribute` of interface is `public`, `static` and `final`, so we don’t need to provide `access modifiers` to the attributes but if we do, compiler doesn’t complain about it either.
2.  By default interface `methods` are [implicitly][] `public` and `abstract`, it makes total sense because the method don’t have body and so that subclasses can provide the method implementation.

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1.  An interface can’t extend any class but it can extend another interface. public interface Shape extends Cloneable\{\} is an example of an interface extending another interface. Actually `java provides multiple inheritance in interfaces`, what is means is that an interface can extend multiple interfaces.

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1.  `implements` keyword is used by classes to implement an interface.
2.  A class implementing an interface must `provide implementation for all of its method unless it’s an abstract class`.

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1.  We should always try to `write programs in terms of interfaces rather than implementations` so that we know beforehand that implementation classes will always provide the implementation and in future if any better implementation arrives, we can switch to that easily.

### 参考 ###

[Interface in Java][].

[provides]: https://dict.youdao.com/w/provides%20/#keyfrom=dict2.top
[implicitly]: https://dict.youdao.com/w/implicitly%20/#keyfrom=dict2.top
[Interface in Java]: https://www.journaldev.com/1601/interface-in-java