![]() Since Java 8, you can also create default methods. Additionally when real object is dereferenced JVM additionally need to remove this weak reference. Java Interfaces Explained with Examples Interface in Java is a bit like the Class, but with a significant difference: an interface can only have method signatures, fields and default methods. For storing simple property it needed two hashmaps and each hashmap by default creates 16 entries by default. Private static final Map widthMap = new WeakHashMap() ĭefault public void setHeight(int height) Private static final Map heightMap = new WeakHashMap() According to OOPs interfaces should act as contract between two systems/parties.īut still i found a way to achieve storing properties in the interface. Java 8 introduced default methods for interfaces using which you can body to the methods. ![]() Method bodies exist only for default methods and static methods. Short answer - you can't do what you want because it is "wrong" in Java.Īn alternative version would be: abstract class AbstractRectangle Interfaces in Java In the Java programming language, an interface is a reference type, similar to a class, that can contain only constants, method signatures, default methods, static methods, and nested types. If you want to require that every class has a certain variable you need to use an abstract class.įinally, you should, generally speaking, not use public variables, so the idea of putting variables into an interface is a bad idea to begin with. It probably would have been better if the creators of Java had not allowed constants in interfaces, but too late to get rid of that now (and there are some cases where constants are sensible in interfaces).īecause you are just specifying what methods have to be implemented there is no idea of state (no instance variables). Also, Lombok can only do its job if the java file was syntactically correct. But I am afraid that just the fact that the field has an initializer modifies the static-ness might be confusing. Any variables that you create are really constants (so be careful about making mutable objects in interfaces).īasically an interface says here are all of the methods that a class that implements it must support. We technically could trigger on uninitialized fields, generate the interface methods and remove the field. The point of an interface is to specify the public API.
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