How to define generic methods in generic interface in Java?

In Java, to define a generic method in a generic interface, you need to: define the generic interface and specify the type parameters. Define a generic method in the interface and specify the method return type and interface type parameters.

Define generic methods in generic interfaces in Java

A generic interface is an interface that contains generic Type type parameters. A generic method is a method defined in an interface that can also contain generic type parameters.

How to define generic methods in generic interfaces:

1. First define a generic interface:

public interface MyGenericInterface<T> {
    // ...
}

1. Define a generic method in the interface:

public interface MyGenericInterface<T> {
    // ...
    
    <R> R myGenericMethod(T t);
}

Where:

• <R> is the type of the return type of the generic method parameter.
• <T> is the type parameter of the interface.

Practical case:

Suppose we have a MyService class, which implements the MyGenericInterface interface:

public class MyService implements MyGenericInterface<String> {
    @Override
    public String myGenericMethod(String s) {
        return s.toUpperCase();
    }
}

Now, we can use the MyService class to call the myGenericMethod method:

MyService service = new MyService();
String result = service.myGenericMethod("hello");
System.out.println(result); // 输出：HELLO

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