Compiler Error J0042

Only classes can implement interfaces

The compiler detected an interface declaration using the implements keyword. Interfaces cannot implement other interfaces. Interfaces can only be implemented by classes. This error usually occurs when an interface is mistakenly implemented instead of extending another interface using the extends keyword.

The following example illustrates this error:

public interface Simple implements color{ 
   // error: 'Simple' cannot implement the 
   // 'color' interface
   
}
interface color {
   // do something meaningful
}

interface pattern extends color{
   //extending an interface is OK here
}