Can we declare interface members as private or protected in java8?

Interface in Java is similar to a class but, it contains only abstract methods and fields which are final and static.

Since all the methods are abstract you cannot instantiate it. To use it, you need to implement this interface using a class and provide body to all the abstract methods in it.

Private members of an interface

If the members of the interface are private you cannot provide implementation to the methods or, cannot access the fields of it in the implementing class.

Therefore, the members of an interface cannot be private. If you try to declare the members of an interface private, a compile-time error is generated saying “modifier private not allowed here”.

Example

In the following Java example, we are trying to declare the field and method of an interface private.

public interface MyInterface {
   private static final int num = 10;
   private abstract void demo();
}

Compile time error

On compiling, the above program generates the following error.

Output

MyInterface.java:2: error: modifier private not allowed here
   private static final int num = 10;
                        ^
MyInterface.java:3: error: modifier private not allowed here
   private abstract void demo();
                             ^
2 errors

Protected members of an interface

In general, the protected members can be accessed in the same class or, the class inheriting it. But, we do not inherit an interface we will implement it.

Therefore, the members of an interface cannot be protected. If you try to declare the members of an interface protected, a compile-time error is generated saying “modifier protected not allowed here”.

Example

In the following Java example, we are trying to declare the field and method of an interface protected.

public interface MyInterface{
   protected static final int num = 10;
   protected abstract void demo();
}

Compile-time error

On compiling, the above program generates the following error.

Output

MyInterface.java:2: error: modifier protected not allowed here
protected static final int num = 10;
^
MyInterface.java:3: error: modifier protected not allowed here
protected abstract void demo();
^
2 errors