InterfaceConstant.java

public interface Employable {
	String MY_CONSTANT = "value"
}

public class MyClass {
	private String theConstant = Employable.MY_CONSTANT;
}

ParentClass.java

public class MyConstants {
	public static final String MY_CONSTANT = "a value";
}

public class MyClass {
	private String theConstant = MyConstants.MY_CONSTANT;
}