Partial interface implementation when you cannot extend a abstract class in java

Question

Suppose I have an interface which has 3 methods. This interface is to be implemented by many classes but the implementation of say method1 will be same in all classes.

I can make an abstract class and give a concrete implementation for method1 and let my classes extend this class.

My question is when I am already extending a class, how do I also extend this abstract class. Java doesn't support it. How should I design in such a scenario?

interface Inf{
 void method1();
 void method2();
 void method3();
}

public abstract class Abs implements Inf{
 void method1(){
  //concrete implementation
 }
}

class Test extends SomeClass implements Inf{
   //here I need method1 implementation and other methods Ill implement
}

class SomeClass{
}

Answer 1

With java 8, you can define default implementation of a method inside the interface.

public interface A {
    default void method1() { System.out.println("Default method1 implementation"); }
    void method2();
    void method3();
}

Answer 2

Java doesn't support Multiple Inheritance. i.e A Class cannot have more than one Base class. What you can do is make the SomeClass to extend Abs class

class SomeClass extends Abs{

}

class Test extends SomeClass implements Inf{
   //here you can get method1 implementation since Someclass extends Abs
}

Note : As said by @anonymous , you can make use of default methods of interface if you work in Java 8

Answer 3

Java doesn't support multiple inheritance. You can make your Abs class to extend SomeClass

class Abs extends SomeClass {

}

class Test extends Abs implements Inf {
}