我们能用 Java 创建一个接口的实例吗？

有没有可能用 Java 创建一个接口的实例？

我曾经读到过，使用内部匿名类，我们可以做到如下所示:

interface Test {
public void wish();
}


class Main {
public static void main(String[] args) {
Test t = new Test() {
public void wish() {
System.out.println("output: hello how r u");
}
};
t.wish();
}
}

cmd> javac Main.java
cmd> java Main
output: hello how r u

这里对吗？

221658 次浏览
小开

Short answer...yes. You can use an anonymous class when you initialize a variable. Take a look at this question: Anonymous vs named inner classes? - best practices?

小开

You can never instantiate an interface in java. You can, however, refer to an object that implements an interface by the type of the interface. For example,

public interface A
{
}
public class B implements A
{
}


public static void main(String[] args)
{
A test = new B();
//A test = new A(); // wont compile
}

What you did above was create an Anonymous class that implements the interface. You are creating an Anonymous object, not an object of type interface Test.

小开

Yes it is correct. you can do it with an inner class.

小开

Normaly, you can create a reference for an interface. But you cant create an instance for interface.

小开
最佳答案

Yes, your example is correct. Anonymous classes can implement interfaces, and that's the only time I can think of that you'll see a class implementing an interface without the "implements" keyword. Check out another code sample right here:

interface ProgrammerInterview {
public void read();
}


class Website {
ProgrammerInterview p = new ProgrammerInterview() {
public void read() {
System.out.println("interface ProgrammerInterview class implementer");
}
};
}

This works fine. Was taken from this page:

http://www.programmerinterview.com/index.php/java-questions/anonymous-class-interface/

小开

Yes we can, "Anonymous classes enable you to make your code more concise. They enable you to declare and instantiate a class at the same time. They are like local classes except that they do not have a name"->>Java Doc

小开

No in my opinion , you can create a reference variable of an interface but you can not create an instance of an interface just like an abstract class.


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