The most obvious difference is that Go doesn't have the implements keyword. All
you have to do to implement an interface is implement the interface's methods,
and the Go compiler will take care of the rest.
This rule leads to the empty interface, interface{}. This interface requires no
methods to be satisfied, and as such is satisfied by all types, including the
builtin types such as int64.
Go interfaces can be satisfied by any kind of type, not just struct types.
type MySpecialInt int
func (m MySpecialInt) String() string {
return fmt.Sprintf("Hello! I'm %d!", int(m))
}
// MySpecialInt implements fmt.Stringer, so printing it with fmt
functions will use the String() method
In Go, you do not have to predeclare your interface types;
func x(y interface{ T() }) { y.T() }
is valid.
Go does not have surrounding types, so the rules about having an interface in a
Java class mean nothing to Go. This is only really relevant in one place: In
Java, if you have an interface method marked private, only the surrounding
class can implement that specific method, not the entire package. In Go, the
entire package is able to implement an unexported method in an interface, but
other packages cannot:
package a
type Y interface { q() }
package b
type X int
func (X) q() { ... } // X does NOT implement a.Y!
However, types in other packages CAN satisfy unexported interfaces:
package a
type y interface { Q() }
package b
type X int
func (X) Q() { ... } // X DOES implement a.y
Go does not have generic types, protected inheritance, static members, abstract
types, final members, or strictfp, so those annotations in Java interfaces are
unavailable. (In Go's case, there is *only* strictfp; the specification implies
in lots of places that IEEE 754 is required, though looking at it again I'm not
sure if a superset of IEEE 754 is acceptable or not...)
Go interfaces may only specify methods; Java interfaces may also specify fields
and nested types. (This makes sense; Go interfaces can apply to any type, and
only structs have "fields", and Go does not have nested types.)
Java interfaces can provide a default implementation for methods that an
implementing class may choose not to override. Go interfaces cannot.
Go does not have the same types of annotations that Java has, so @interface is
meaningless. For details on Go's closest approximation, see struct tags.
Go does not have functional interfaces or interface literals.
> On Oct 8, 2016, at 9:14 AM, Fei Ding <[email protected]> wrote:
>
> Recently I've been asked a question which is, what's the difference between
> Golang and Java about interface?
>
>
>
> I know there are some 'syntax-sugar level' differences, what I am interested
> is anything beneath the ground, like how does Golang and Java implement
> interface? What's the biggest difference? Which one is more efficient? Why?
>
>
>
> Could anyone post blog links or source code about this topic? The only code I
> can find is in src/runtime/iface.go, but I cannot understand it or get
> anything useful by myself yet. Source code is better.
>
>
>
> Thanks.
>
>
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