* Modifies this set by adding e to the set. When the interface mentions placeholder type If the annotated method does not actually override anything, the compiler issues a warning. For two reasons, the Override annotation is useful. The Override annotation denotes that the child class method overrides the base class method. Generic interface, non-generic implementation. The Override annotation is a standard Java annotation that was first introduced in Java 1.5. We still write specs at the level of our abstract model of sets. This annotation informs the compiler that the method must have the same signature as one of the methods in the interface we. The story for these mutators is basically the same as for the observers. * e element to remove */ public void remove (E e) * If e is not found in the set, has no effect. ** Modifies this set by removing e, if found. * e element to add */ public void add (E e) example mutator operations /** Modifies this set by adding e to the set. These specs should apply to any valid implementation of the set ADT. Notice how the specs are in terms of our abstract notion of a set it would be malformed to mention the details of any particular implementation of sets with particular private fields. * true iff this set contains e */ public boolean contains (E e) * the number of elements in this set */ public int size () example observer operations /** Get size of the set. Operation is implemented as a static factory method.Īnd the compiler will understand that the new When the name of super's methods changing, the compiler can notify that case, which is only for keep consistency with the super and the subclass. ** MyString represents an immutable sequence of characters. The annotation Override is used for helping to check whether the developer what to override the correct method in the parent class or interface. Using an interface instead of a class for the ADT, we can support multiple implementations: If you declare a subtype in Java - implementing an interface is our current focus - then you must ensure that the subtype’s spec is at least as strong as the supertype’s. When we declare a class that implements an interface, the Java compiler enforces part of this requirement automatically: for example, it ensures that every method in A appears in B, with a compatible type signature.Ĭlass B cannot implement interface A without implementing all of the methods declared in A.īut the compiler cannot check that we haven’t weakened the specification in other ways: strengthening the precondition on some inputs to a method, weakening a postcondition, weakening a guarantee that the interface abstract type advertises to clients.
That means B is only a subtype of A if B’s specification is at least as strong as A’s specification. In terms of specifications: “every B satisfies the specification for A.” “B is a subtype of A” means “every B is an A.” Objects, or objects of another class that implements Objects: we cannot create instances of an interface.
#Override annotation java interface code#
Unfortunately, the compiler doesn’t check for us that the code adheres to the specs of those methods that are written in documentation comments. Java’s static type checking allows the compiler to catch many mistakes in implementing an ADT’s contract.įor instance, it is a compile-time error to omit one of the required methods, or to give a method the wrong return type. , but we couldn’t have both representations for the ADT in the same program. We explored two different representations for When an abstract data type is represented just as a single class, without an interface, it’s harder to have multiple representations. The implementation is kept well and truly separated, in a different class altogether.Īnother advantage is that multiple different representations of the abstract data type can co-exist in the same program, as different classes implementing the interface. The client can’t create inadvertent dependencies on the ADT’s rep, because instance variables can’t be put in an interface at all. The interface is all a client programmer needs to read to understand the ADT. One advantage of this approach is that the interface specifies the contract for the client and nothing more.
So one way to define an abstract data type in Java is as an interface, with its implementation as a class implementing that interface. Is a useful language mechanism for expressing an abstract data type.Īn interface in Java is a list of method signatures, but no method bodies.Īn interface if it declares the interface in itsĬlause, and provides method bodies for all of the interface’s methods.
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