Issue in returning interface as return type in Java

I have the following code:

Filename: A.java

package test1

public interface A {
   int get();
   int set();
}

Filename: B.java

package test1
public class B implements A {

    int get() {
       ...
    }

    int set() {
     ....
    }
}

Filename: C.java

package test2

import test1.A;
import test1.B;

publc class C {

        public A getNum() {
             B test = null;

             return(test);
        }
}

When I compiled the above code in Eclipse--> Sample Java Project, It is working fine. But when I compil开发者_StackOverflowed the same code in Android, It is throwing the following error:: Method C.getNum returns unavailable type A;

Please let me know, where I am going wrong.

Thanks in advance, Kranti

Inteface and Implements are not java keywords. You should use interface and implements instead. Java is case sensitive. Type A is unavailable on the class path due to other compilation errors.

the following code should work:

public class Test {
    interface  A {
        int get();
        int set();
    }

    class B implements A {

        @Override
        public int get() {
            return 0;
        }

        @Override
        public int set() {
            return 0;
        }
    }

    class C {
        public A getNum(){
            A a = new B();
            return a; 
        }
    }
}

I've produced that code based on your example. But you know I cannot imagine what this code is useful for.

Assuming A.java, B.java are in test directory and C.java is in the root directory the above code has many issues

1. Interface and Implements should be small caps i.e "interface" and "implements"
2. interface methods are public even if not declared. So when implementing it in B both get and set should be public
3. A.java and B.java should have package test; as the first line
4. You need to import test.A; import test.B;
5. There is no class declaration for C
6. B test = 0; is wrong. It should be either B test = null; or B test = new B(); depending on what you plan to use. 0 is an integer and can't be cast to B
7. return B is not valid as B is a class name. You probably intended return test;

Here's a modified code

A.java

package test;
public interface A {
    int get();
    int set();
}

B.java

package test;
public class B implements A {

    public int get() {
        return 0;
    }

    public int set() {
        return 0;
    }
}

C.java

import test.A;
import test.B;

public class C {
    public A getNum() {
        B test = new B();

        return test;
    }
}

The problem I see is just to mention the package declaration i.e. package test1 in the interface A file.