Java multiple interfaces implementation

Question

the setting is like this.
I have multiple interfaces (i.e. A,B,C) and I have classes (Z and Y) to implements them
X implements A,B{} and Y implements A,C{} and Z implements B,C{}

Some functions in interface A,B,C have the same definition and I don't want to retype them in each class, how should I do?
I did google it, and notice that one solution is to use a handy keyword default in the interface. But what if I am prohibited from using this keyword, like the code is compatible with version prior than Java8?

Is there a better way to handle this problem?

Can you describe the problem more clearly? If A, B and C all share a method named f with the same signature, and W implements all three interfaces, you still just need to write the implementation once. — Sweeper
– Sweeper, Commented Oct 15, 2018 at 16:38
You should consider using java 8 or even 11 since older versions are not supported by Oracle and most people have migrated to java 8 or 11. — NielsNet
– NielsNet, Commented Oct 15, 2018 at 16:40
let A has functions: a1,a2,a3 B has b1,b2,b3 C has c1,c2,c3 a1, b1 and c1 have the same definition, otherwise different definition — Hawii Hawii
– Hawii Hawii, Commented Oct 15, 2018 at 16:42

Saurabh Oza · Accepted Answer · 2018-10-20 17:08:50Z

1

Then you should go with abstract class and provide some default implementation for the common methods in different interfaces as below.

interface A {
    void m1();
    void common();
}

interface B {
    void m2();
    void common();
}

abstract class ABClass implements A, B {

    public void common() {
    System.out.println("Default");
}

Class X extends ABClass {
}

answered Oct 20, 2018 at 17:08

Saurabh Oza

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Comments

GAdams · Accepted Answer · 2018-10-15 16:39:02Z

1

Instead of gaining these methods through inheritance and having to extend mutliple classes to get your definitions in, you could favor composition and take a class that implements the method you want to reuse as a parameter. Keeping it as a private final member variable, you can call this common method in a generic way.

answered Oct 15, 2018 at 16:39

GAdams

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1 Comment

Hawii Hawii Over a year ago

won't this make the code less comprehensible? I am still learning OOP, can you provide me a simple example? thank.

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